Waterfowl management handbook

              WATERFOWL MANAGEMENT HANDBOOK
13.1.1. Nutritional Values of Waterfowl Foods
Leigh H. Fredrickson and Fredric A. Reid
Gaylord Memorial Laboratory School of Forestry, Fisheries and Wildlife University of Missouri−Columbia Puxico, MO 63960
Over 40 species of North American waterfowl use wetland habitats throughout their annual cy­cles. Survival, reproduction, and growth are depend­ent on the availability of foods that meet nutritional requirements for recurring biological events. These requirements occur among a wide variety of environ­mental conditions that also influence nutritional de­mands. Recent work on nesting waterfowl has identified the female’s general nutrient needs for egg laying and incubation. Far less is known about nutritional requirements for molt and other por­tions of the life cycle, particularly those during the nonbreeding season. Although information on spe­cific requirements for amino acids and micronutri­ents of wild birds is meager, the available information on waterfowl requirements can be used to develop waterfowl management strategies. For example, nutrient content of foods, nutritional re­quirements of waterfowl, and the cues waterfowl use in locating and selecting foods are all kinds of in­formation that managers need to encourage use of habitats by feeding waterfowl. Waterfowl nutri­tional needs during the annual cycle and the nutri­tional values of natural foods and crops will be discussed below.
Composition of Waterfowl Foods
Compared to the nutritional information on many agricultural crops, the composition of wild
foods is poorly documented. Nevertheless, the avail­able information on nutritional quality of wild foods, in conjunction with known waterfowl require­ments, provides general guidelines for manage­ment. Terminology commonly used when discussing the nutritional values of foods or requirements for waterfowl include the following:
Basal metabolic rate (BMR)—The lowest level of metabolism necessary for basic body functions for an animal at rest. Gross energy—The amount of energy (often expressed in 1000 calories = 1 kcal) produced when a food sample is ignited in a bomb calorimeter. Gross energy represents the most common nutritional information available, because techniques to determine gross energy are relatively simple and costs are minimal. Metabolizable energy—The amount of energy that can be utilized for metabolic processes by an animal. Metabolizable energy is more complicated to determine than gross energy—animals must be fed a diet of food containing a known amount of gross energy, and the portion excreted as feces, urine, and gases must be identified and quantified. Proximate analysis—A chemical process to identify the major components in foods. Samples must be handled carefully to ensure that chemical composition represents the nutritional content. The food is first ground to a fine homogenate, then dried to determine water content. Components identified by proximate analysis include the following:
•
Fats or lipids —The most concentrated energy sources in foods. Fats occur as structural compo­nents and serve as insulation or as energy stores.
•
Ash—Mineral content.
Fish and Wildlife Leaflet 13.1.1. • 1988 1 •
Crude Fiber—Least digestable fraction in foods that includes cellulose, hemicellulose, or lignin. Waterfowl lack rumens; thus, little fiber is di­gested.
•
Nitrogen-free extract (NFE)—Highly digestible carbohydrates.
•
Protein—Compounds containing nitrogen that are major components of muscle tissue, animal cell membranes, and feathers; also active as en­zymes, hormones, and clotting factors in blood. These serve many different functions.
More sophisticated testing provides identifica­tion of the specific composition of proteins and fats:
•
Amino acids—Mixtures of 20 to 25 different amino acids, linked by peptide bonds, form plant and animal proteins.
•
Essential amino acids —The 10 amino acids that must come from the diet because of the inability of an animal’s metabolic pathway to produce them.
•
Fatty acids—Components of fats with varying mo­lecular weight and number of double bonds. Unsaturated fatty acids such as palmitoleic, oleic, and linoleic acids are important in waterfowl.
Information is generally available on the gross energy of foods (Tables 1 and 2), but metabolizable energy and outputs of proximate analyses including the amount of fat, fiber, ash, or nitrogen-free ex­tract of these same foods are rarely identified (Ta­ble 3). Proteins supply the essential amino acids and are in high demand during egg laying and molt. Fats or lipids serve as energy reserves, as struc­tural elements in cells, and as sterol hormones. Ash indicates the mineral content. Crude fiber is a meas­ure of the least digestible food components, whereas NFE provides an estimate of the highly digestible carbohydrates.
Food quality is best predicted when information is available on metabolizable energy, ash, protein, fat, and NFE. Protein values are reported for about half of the foods that have energy values, but the content of fat, fiber, ash, or NFE is identified for less than one-third. Foods with a very high fiber con­tent generally have lower levels of metabolizable or usable energy because fiber is poorly digested by wa­terfowl. In some cases, values from chemical analy­ses can be misleading. Crude protein content may be high, but the form of the protein or chemical in­hibitors within the food may reduce the amount us­able by the bird. For example, soybeans have a high level of crude protein, but only a small portion is available to waterfowl because of inhibitors. Water­fowl require a balance of amino acids. Some foods, such as crustaceans, usually have a better balance of amino acids than do insects and spiders. Certain
Table 1. Chemical composition of some common waterfowl plant foods. Values represent averages from the literature.
Gross energy
Common namea
(kcal/g)
Fat
Fiber
Ash
NFE
Protein
Sticktights
5.177
15.0
19.7
7.2
27.5
25.0
Schreber watershield
3.790
2.9
36.7
4.8
45.9
9.3
Pecan hickory
7.875
40.8
19.0
12.6
35.1
8.4
Chufa flatsedge (tubers)
4.256
6.9
9.0
2.5
55.4
6.7
Hairy crabgrass
4.380
3.0
11.1
9.7
59.4
12.6
Barnyardgrass
3.900
2.4
23.1
18.0
40.5
8.3
Rice cutgrass
3.982
2.0
10.6
9.5
57.8
12.0
Fall panicum
4.005
3.1
16.8
16.1
50.1
12.3
Smartweed
4.423
2.8
22.0
7.5
—
9.7
Pennsylvania smartweed
4.315
2.3
21.8
4.9
65.3
9.0
Pin oak
5.062
18.9
14.7
1.6
58.6
6.4
Willow oak
5.296
20.6
14.0
1.7
55.3
5.1
Curly dock
4.278
1.2
20.4
6.9
—
10.4
Duck potato
4.736
9.0
10.8
4.9
55.5
20.0
Milo
4.228
3.1
6.0
3.5
72.2
10.2
Corn
4.435
3.8
2.3
1.5
79.8
10.8
Common soybean
5.451
20.5
5.4
6.2
27.1
39.6
Common duckweed
4.235
3.5
11.3
10.7
49.8
25.7
River bulrush (rhizomes)
4.010
—
—
—
—
—
a For alternative common names and scientific names consult Appendix.
2
Fish and Wildlife Leaflet 13.1.1.
• 1988 Table 2. Chemical composition of some common waterfowl invertebrate foods.
Gross energy Protein Invertebrate (kcal/g) (%)
Water boatmen 5.2 71.4 Back swimmers 5.7 64.4 Midges 4.6 61.2 Water fleas 4.0 49.7 Amphipods (Hyallela azteca) 4.9 47.6 Amphipods (Gammarus spp.) 3.8 47.0 Cladocera (unclassified) 2.7 31.8 Pond snails 1.0 16.9 Orb snails 1.0 12.2
amino acids can be synthesized by waterfowl, but the essential amino acids must be acquired in the diet.
Because values for metabolizable energy are re­ported for individual food items rather than as com­binations of foods normally consumed by wild waterfowl, nutritional information is not always ac­curate. Synergistic interactions among foods during digestion are more difficult to identify compared to the usable energy available from a single food item fed separately. Thus, providing a nutritionally bal­anced diet from wild and domestic foods, alone or in combination, continues to be a perplexing challenge facing wetland managers.
The Energetic Costs of Waterfowl Activities
Wild animals must provide for general body maintenance and for processes that require addi­tional nutrients, such as growth, reproduction, and migration. The BMR includes the demands for energy of an animal that is at rest. Basal costs for locomotion, digestion, reproduction, or thermoregu­lation at extreme temperature ranges are not in­cluded. Large body sizes allow waterfowl to use their body reserves to meet the demands of mainte­nance and other demanding processes. For exam­ple, arctic−nesting geese transport all of their protein and energy needs for laying and incuba­tion with them to arctic nesting grounds. Such spe­cies may lose nearly 50% of their body weight by the time their clutches hatch. Reserves for migra­tion are particularly important in some waterfowl such as Pacific populations of brant. In their 3,000−mile journey from Alaska to Mexico, they lose one-third of their body weight (about 1.87 lb of fat) in a few days.
Waterfowl engage in a variety of activities that have high energetic costs. The locality and the envi­ronmental conditions under which these activities occur determine the energetic expenditures for each event. These are usually expressed in relation to the basal metabolic rate for an animal at rest.
Activities such as swimming, preening, forag­ing, or courtship are more energetically costly. Flight is the most expensive activity with estimates ranging from 12−15 × BMR. Diving is less costly (i.e., 3.5 × BMR). Furthermore, temperatures have important effects on energetic requirements. For ex­ample, captive mallards will increase their metabo­lic rate above the basal level by 2.1 × at 0°C and by
2.7 × at −20°C. Wild ducks and geese reduce the fre­quency of their feeding flights under extreme cold to conserve energy. Determining actual energetic costs of activities is difficult in the field; hence, the values for wild birds are usually based on estimates rather than actual measurements.
The general nutritional requirements for biologi­cal events in the annual cycle are known for an in­creasing number of waterfowl. The best estimates are those for breeding birds (Table 4), whereas far less is known about nonbreeding requirements.
Table 3. Metabolizable energy of some common waterfowl foods.
Metabolizable energy Taxon Test animal (kcal/g)
Water flea Blue-winged teal 0.82 Amphipod (Gammarus spp.) Blue-winged teal 2.32 Pond snail Blue-winged teal 0.59 Coast barnyardgrass Duck (male) 2.63 Coast barnyardgrass Duck (female) 2.99 Rice cutgrass Duck (male) 3.00 Common duckweed Blue-winged teal 1.07 Pennsylvania smartweed Dabbling duck (male) 1.12 Pennsylvania smartweed Dabbling duck (female) 1.10
Fish and Wildlife Leaflet 13.1.1. • 1988 3 Table 4. Nutritional requirements for breeding waterfowl compared to the composition of corn and common native foods.
Requirements
breeding
Plants Foods
ducks/geese
Corn
Acorns
Barnyardgrass
Pigweed
Energy 2,900a 3,430a 5,577b 4,442b 4,623b Protein (%) 19 8.7 6.0 12.5 22.0 Methioninec 2.0 0.18 — — — Ca (%) 2.7 0.02 0.24 0.13 1.72 Mg (ppm) 350 5 — 69 35
a = kcal ME/kg b = Gross energy (not metabolizable energy) c = % of protein
Note that no single food supplies a diet that meets all energy, protein, or micronutrient needs of breed­ing waterfowl. Likewise, activities other than breed­ing have varying costs in relation to specific nutrient energy and differ greatly from reproduc­tion, where a mix of energy, minerals, and protein are required to supply the needs of egg-laying fe­males.
Food Quality in Relation to Deterioration and Habitat Conditions
The quality of plant foods is largely determined by heredity, but other factors, such as soil nutrients and environmental conditions during the growing season, are important. For example, seeds having a high fat content may vary greatly in energy content among seasons because of environmental condi­tions. The supply of minerals is closely related to the mineral concentrations in water.
One of the major problems facing waterfowl managers is deterioration of seeds during flooding, but information on rates of deterioration is only available for a few seeds. Soybeans break down very rapidly; nearly 90% of the energy content is lost dur­ing 3 months of flooding, whereas corn loses only 50% during a similar period of flooding (Table 5). Breakdown of wild seeds is variable. Hard seeds such as bulrush decompose slowly, whereas softer seeds such as common barnyardgrass deteriorate 57% after 90 days under water. Such variations have important implications for the timing of flood­ing for waterfowl (Table 6). If some seeds are sub­merged for a month or more before waterfowl are present, much of the food value will be lost because of deterioration.
Supplying Nutritional Needs for Waterfowl
The large body sizes of waterfowl enable them to store nutrients as body reserves. In some cases nutrients for an upcoming stage in the life cycle are acquired at a distant wetland and transported as body reserves. The best known examples are the transport of fats, calcium, and protein by arctic-nesting geese from wintering and migrational stop­overs to breeding habitats. Because waterfowl store body reserves, managers should make an effort to supply required nutrients throughout the annual cycle rather than supplying nutrients solely for events at the time they occur.
Identifying shortfalls in nutritional needs is be­coming more of a reality as the requirements for free-living animals are identified. Waterfowl are well adapted to the dynamics of natural wetland sys­tems. Mobility and foraging adaptability are behav-
Table 5. Deterioration of selected seeds after 90 days of flooding.
Decomposition Plant name (%)
Soybean 86 Barnyardgrass 57 Corn 50 Common buckwheat 45 Milo 42 Giant bristlegrass 22 Pennsylvania smartweed 21 Cultivated rice 19 Water oak (acorns) 4 Hemp sesbania 4 Horned beakrush 2 Saltmarsh bulrush 1
4 Fish and Wildlife Leaflet 13.1.1. • 1988 Table 6. Comparison of deterioration of 100 lb of five selected seeds in relation to different flooding schedules. Estimates assume a constant daily rate of deterioration.
Percent Remaining
15 September
15 October
15 Novemeber
15 December
Flooding Date
18 August
Soybeans
71
43
14
0
Corn
83
67
50
33
Millet
81
62
43
24
Giant bristlegrass
93
85
78
71
Smartweed
93
85
79
72
Total percent remaining
84
68
53
40
15 September
Total percent remaining
84
68
53
15 October
Total percent remaining
84
68
15 November
Total percent remaining
84
ioral characteristics that enable waterfowl to ac­quire needed resources. Dynamic wetlands supply a variety of food resources that allow waterfowl to feed selectively and to formulate nutritionally ade­quate diets from a variety of sites. Although a single wetland site may not provide adequate food for all requirements, management areas with a variety of wetlands or flooding regimes usually have a mix of habitats that provide all nutritional requirements.
Because a variety of strategies exists within and among waterfowl species (wintering, migration, or breeding), not all individuals or species require similar resources simultaneously. Thus, a diverse habitat base is a logical approach to meet the vari­ous needs of waterfowl. Furthermore, when suitable food and cover are within daily foraging range, ac­quisition of required resources is enhanced. A good rule of thumb is to provide many wetland types or food choices within a 10-mile radius of waterfowl concentrations. Some species such as snow geese have far greater foraging ranges, but they are the exception rather than the rule.
Appropriate management requires preserva­tion, development, and manipulation of manmade and natural wetland complexes. Such an approach provides nutritionally balanced diets for diverse wa­terfowl populations. Where natural wetlands re­main intact, they should be protected as unique components of the ecosystems. The protection of natural systems and the development and manage­ment of degraded systems increases choices of habi­tats and foods for waterfowl. Likewise, the provision of adequate refuge areas where birds are protected from disturbance is an essential ingredient to en­sure that food resources are available to waterfowl and can be used efficiently.
Suggested Reading
Hoffman, R.B., and T.A. Bookhout. 1985. Metabolizable energy of seeds consumed by ducks in Lake Erie marshes. Trans. N. Am. Wildl. Nat. Resour. Conf. 50:557−565.
National Research Council. 1977. Nutrient requirements of domestic animals. No. 1. Nutrient requirements of poultry. Natl. Acad. Sci., Washington, D.C. 62 pp.
Neely, W.W. 1956. How long do duck foods last underwater? Trans. N. Am. Wildl. Conf. 21:191−198.
Prince, H.H. 1979. Bioenergetics of postbreeding dabbling ducks. Pages 103−117 in T.A. Bookhout, ed. Waterfowl and wetlands: an integrated review. Proc. 1977 Symp., North Cent. Sect., The Wildl. Soc., Madison, Wis. 147 pp.
Robbins, C.T. 1983. Feeding and wildlife nutrition. Academic Press, New York. 343 pp. Sugden, L.G. 1971. Metabolizable energy of small grains for mallards. J. Wildl. Manage. 35:781−785.
Fish and Wildlife Leaflet 13.1.1. • 1988 5 Appendix. Common and Scientific Names of Plants and Animals Named in Text.
Plants
Pigweed . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Amaranthus sp. Devils beggarticks or sticktights .. .. .. .. .. .. .. .. .. .. .. .. Bidens frondosa Schreber watershield .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Brasenia schreberi Pecanhickory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carya illinoensis Chufa flatsedge . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Cyperus esculentus Hairy crabgrass. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Digitaria sanguinalis Common barnyardgrass or Japanese millet .. .. .. .. .. .. .. .. .. Echinochloa crusgalli Coast barnyardgrass, wild millet, or watergrass . .. .. .. .. .. .. .. Echinochloa walteri Commonbuckwheat .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Fagopyrum esculentum Commonsoybean .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Glycine max Rice cutgrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Leersia oryzoides Commonduckweed . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Lemna minor Cultivatedrice . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Oryza sativa Fall panicum or panicgrass . . . . . . . . . . . . . . . . . . . . . . . . . . Panicum dichotomiflorum Curltop ladysthumb or smartweed .. .. .. .. .. .. .. .. .. .. .. Polygonum lapathifolium Pennsylvania smartweed .. .. .. .. .. .. .. .. .. .. .. .. .. .. Polygonum pensylvanicum Pinoak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus palustris Willowoak . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Quercus phellos Wateroak .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Quercus nigra Hornedbreakrush . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Rhynchospora corniculata Curlydock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rumex crispus Common arrowhead or duckpotato .. .. .. .. .. .. .. .. .. .. .. Sagittaria latifolia River bulrush or three-square bulrush .. .. .. .. .. .. .. .. .. .. Scirpus fluviatilus Saltmarsh bulrush or bulrush . .. .. .. .. .. .. .. .. .. .. .. .. Scirpus robustus Hemp sesbania . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Sesbania exalta Giant bristlegrass or giant foxtail .. .. .. .. .. .. .. .. .. .. .. . Setaria magna Common sorghum or milo . .. .. .. .. .. .. .. .. .. .. .. .. .. Sorghum vulgare Indian corn or corn . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Zea mays
Birds
Blue-wingedteal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anas discors
Mallard . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas platyrhynchos
Brant .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Branta bernicla
Snow goose .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Chen caerulescens
Invertebrates (Families)
Midges .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..Chironomidae
Waterboatmen .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Corixidae
Waterfleas .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Daphnidae
Pond snails .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Lymnaeidae
Backswimmers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Notonectidae
Orb snails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Planorbidae
UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE
Fish and Wildlife Leaflet 13
Washington, D.C.  •• 1988
6 Fish and Wildlife Leaflet 13.1.1. •• 1988 WATERFOWL MANAGEMENT HANDBOOK
13.1.2 Life History Traits and Management of the Gadwall
James K. Ringelman
Colorado Division of Wildlife 317 West Prospect Road Fort Collins, CO 80526
The gadwall is widely distributed throughout the western two-thirds of North America. Although its primary breeding habitat is in the drought-prone and degraded waterfowl habitats of the north­ern Great Plains, its continental population has re­mained relatively stable while those of most other dabbling ducks have declined. Some unique life his­tory traits may in part be responsible for the resil­ience of gadwall populations. These unique attributes, which are important for gadwall manage­ment, are the subject of this leaflet. Readers inter­ested in general references on gadwall biology and natural history are referred to Bellrose (1980) or Palmer (1976).
Distribution
Gadwall breeding populations reach their high­est densities in the mixed-grass prairies of the northern Great Plains and the intermountain val­leys of the western United States (Fig. 1). The parklands and shortgrass prairies contain relatively fewer breeding birds. Some portions of the Pacific, Atlantic, and Alaskan coasts also have important breeding populations.
The primary migration corridor for gadwalls originates in the prairies and extends through the low plains region of the United States, including Ne­braska, Kansas, eastern Colorado, Oklahoma, Texas, Louisiana, and into Mexico. Secondary mi-
Species Profile—Gadwall
Scientific name: Anas strepera Weight in pounds (grams):
Adults—male 2.1 (953), female 1.8 (835)
Immatures—male 1.9 (858), female 1.7 (776)
Age at first breeding: 1 or 2 years
Clutch size: 10, range 5 to 13
Incubation period: 25 days
Age at fledging: 48−52 days
Nest sites: Tall, dense herbaceous vegetation or small shrubs within 1,000 feet of water, often near the site used the previous year
Food habits: Herbivorous, except during spring when some aquatic invertebrates are consumed
gration routes link the prairies with the Pacific Northwest, northern and central California, and northern Utah. From Utah, birds migrate to winter­ing areas in central and southern California and Mexico. Gadwall also migrate along diagonal routes from the Great Plains to the central and southern Atlantic coast.
Major wintering areas include coastal areas of Louisiana and Texas, south along the east coast of Mexico to the Yucatan Peninsula; the central and southern Atlantic coast; the Central Valley of Cali­fornia; and much of the west coast of Mexico.
Population Status and Harvest
Despite drought and widespread waterfowl habi­tat destruction in the 1970’s and 1980’s, the size of the gadwall population in North America has re-
Fish and Wildlife Leaflet 13.1.2. •• 1990 1 Fig. 1. Distribution of breeding and wintering gadwalls in North America.
mained relatively stable compared with populations of mallards and northern pintails (Fig. 2). Breeding gadwall are increasing in the Great Basin region, the intermountain valleys of the Rocky Mountains, and in the Pacific Flyway. The reproductive success of gadwall may be enhanced because of the ten­dency of this species to use semipermanent wet­lands, home to traditional nesting sites where hens were previously successful, and to concentrate in se­cure nesting locations such as islands. The gadwall is also a lightly-harvested species; gadwall make up 4.2% of the continental population of breeding ducks but compose only 2.5% of the duck harvest.
Spring Migration and Breeding
Gadwalls depart wintering areas by March or early April (Fig. 3). They are among the last birds to arrive on the nesting grounds, and yearlings usu­ally arrive later than older birds. Three to four weeks pass before most birds begin laying, during which time females acquire the fat and protein re­serves needed for egg production. Compared to other dabbling ducks, a high percentage of yearling gadwalls do not attempt to nest. Birds older than one year initiate nests first, often in mid-May. Most female gadwall that nest successfully return to ar­eas used the previous year. When drought occurs on their prairie breeding grounds, many gadwalls mi­grate north into central and northern Canada.
Shortly after arrival on the nesting grounds, pairs establish territories on seasonal and semiper­manent wetlands. Gadwall also tend to use open
Fig. 2. Continental breeding population of gadwalls (1970−89) compared with breeding populations of mallards and northern pintails.
2 Fish and Wildlife Leaflet 13.1.2. •• 1990 brackish or alkaline waters. Since semipermanent ponds are less susceptible to annual drought events than are ephemeral and temporary wetlands, the gadwall’s preference for deepwater habitats may be beneficial during drought.
Aquatic invertebrates make up about half of the gadwall’s diet during spring and summer (Table 1), and up to 72% during egg laying. Gadwalls consume the green portions of aquatic plants almost exclu­sively during the non-nesting season (Table 1). Most plants and animals consumed by gadwalls are adapted to semipermanent or permanent wetlands, so drawdowns of managed impoundments should be infrequent (6−8 years) in wetlands managed for this species. A small percentage of ponds in a wetland community should be drawn down during a single season, so that several "familiar" wetlands remain within the home range of gadwall pairs.
Nests are usually located in dry upland sites un­der clumps of shrubs or in herbaceous vegetation. Although nests average 1,000 feet (300 m) from water, sites up to 1.2 miles (1.9 km) away may be used. Nests in the valleys of the intermountain West are commonly found in baltic rush, nettle, and under small shrubs. In the northern Great Plains, fields of seeded native grasses usually receive the greatest use, followed by introduced grasses and un­plowed, native prairie. Shrubs such as western snowberry and Woods rose also provide attractive nesting cover. Growing grainfields receive little use, and gadwalls avoid stubble and summer fallow areas.
Areas of dense vegetation, such as a grass-leg­ume mixture, provide beneficial nesting cover for gadwalls. Residual cover from the previous year’s growing season, although not as important for the late-nesting gadwalls as it is for other early-nesting
Fig. 3. The chronology of important life history events in the annual cycle of the gadwall.
Fish and Wildlife Leaflet 13.1.2. •• 1990 3
Table 1. Seasonal food habits of adult gadwall. Within seasons, the list of food items is arranged in order of importance in the diet.Vegetative foods refer to green portions of plants unless otherwise noted.
Season, food type,
and % volume in diet
Common name
Habitat and location
Spring and summer
Plant foods (54%)
Filamentous algae
Brackish, subsaline, and
Widgeongrass
saline wetlands of
Muskgrass
North Dakota.
Sago pondweed
Elodea
Animal foods (46%)
Fairy shrimp
Seed shrimp
Water fleas
Midges
Beetle larvae
Fall and winter
Plant foods (95%)
Filamentous algae
Fresh, intermediate, and
Dwarf spikerush
brackish marshes in
Widgeongrass
Louisiana
Spiked watermilfoil
Baby pondweed
Animal foods (5%)
Seed shrimp
Plant foods (91%)
Fragrant flatsedge
Fresh and brackish tidal
Redroot sedge
impoundments in South
Widgeongrass
Carolina
Animal foods
none listed
ducks, nonetheless affords important cover in many nesting habitats. Residual cover can become lodged and matted over several years, so burning or me­chanical manipulations are sometimes needed to re­juvenate nesting areas.
Gadwalls often use islands as nesting sites be­cause the water barrier reduces nest losses from mammalian predators. The high nest success typi­cal of islands, coupled with the homing tendencies of gadwalls, contribute to nesting densities as high as 200 nests/acre (493 nests/ha). Suitable nesting is­lands should be 0.2−1.2 acres (0.1−0.5 ha) in size, elongated in shape, and separated from the main­land by at least 500 feet (150 m) of water that re­mains 3 feet (0.9 m) deep during the nesting season. Although islands can be incorporated into the initial impoundment designs or constructed when a wet­land has been dewatered, the construction cost is high even when amortized over the expected life of the island. Additionally, vegetation can be difficult to establish on newly constructed islands. A more cost-effective approach is to cut-off an existing pen­insula from the mainland, thereby saving most of the cost of earth moving and vegetation estab­lishment. As valuable as nesting islands can be, managers must provide a diversity of wetlands for pairs and broods to complement the secure nesting habitat afforded by islands.
Brood-rearing hens will move ducklings up to
1.2 miles (1.9 km) to brood habitat. Gadwall duck­lings initially consume equal amounts of plant and animal foods, but consumption of animal food peaks at 2 weeks of age as vegetative matter begins to dominate their diet (Table 2). The average brood size at time of fledging (50 days old) is 6.2 ducklings per brood.
Post-breeding Dispersal
After hens have incubated for about 2 weeks, males abandon their breeding territories and con­centrate on large permanent or semipermanent wet­lands near the nesting area. Males, which are flightless for 25−28 days beginning in mid-July, form molting rafts of several hundred to thousands of individuals. These birds often occupy open water areas that contain beds of submersed aquatic vege­tation, their primary food (Table 1). Unlike mal­lards and other secretive species that seek heavy vegetative cover when flightless, gadwalls often as­sociate with American wigeons and diving ducks and loaf on the bare shorelines of islands or main-
Fish and Wildlife Leaflet 13.1.2. •• 1990 4
Table 2. Food habits of gadwall ducklings. The list of food items is arranged in order of importance in the diet. Vegetative foods refer to green portions of plants unless otherwise noted.
Food type and % dry weight in diet
Common name
Habitat and location
Plant foods (90%)
Baby pondweed
Freshwater prairie wetlands
Filamentous algae
in southern Alberta
Slough grass seeds
Duckweed
Muskgrass
Coontail
Animal foods (10%)
Beetle larvae
Midges
Water fleas
land stretches that are free from human distur­bance. Female gadwalls molt 20−40 days after the males, usually singly or in small flocks. However, moderate-to large-sized wetlands of a permanent or semipermanent nature, expanses of open water with submersed vegetation, and open shorelines se­cure from human disturbance are important charac­teristics of molting habitat for both sexes.
Fall Migration
Most gadwalls begin their fall migration in early September, and none remain on northern breeding grounds by late October. However, be­cause of their late breeding and molt chronology, some females remain flightless into late September and early October. These birds, which are probably hens that successfully completed second nests after their first clutch was destroyed, may be subject to hunting before they fully regain flight capabilities. Since opening of the hunting season typically occurs as early as possible (the first week in October) in the northern Great Plains and intermountain ba­sins of the West, some local populations of late-molt­ing female gadwalls may be subject to high hunting mortality during early fall.
Because gadwall consume a diet composed al­most exclusively of green, submersed aquatic vege­tation during fall (Table 1), traditional wetland management techniques such as moist-soil im­poundments, which encourage the production of seed producing annuals, are not as attractive to gad­walls as they are to most other dabbling ducks. Ce­real grains and row crops so highly sought by mallards, pintails, and green-winged teal also re­ceive little use by gadwalls, but flooded ricefields are used by gadwalls in the Central Valley of Cali­fornia. Wetland management to benefit gadwall should be directed at maintaining large wetlands with stable water levels suitable for the growth of submersed aquatic vegetation. Although it is most desirable to promote the growth of native vegetation present in a wetland, managers can establish stands of submersed vegetation by seeding or trans­planting tubers and whole plants. Wildlife plant nurseries sell seeds and tubers for this purpose. Ex­treme water level fluctuations or poor water quality may inhibit the growth of submersed vegetation. Stabilization of water levels through control struc­tures or augmentation of water flows during dry pe­riods may be necessary. Removal of rough fishes, which increase water turbidity and degrade water quality, often dramatically improves stands of sub­mersed vegetation.
Winter
Gadwalls reach their highest winter densities on the fresh, intermediate, and brackish marshes of the Louisiana coast. There, as elsewhere, their diet is composed almost entirely of vegetative foods (Ta­ble 1) obtained in water 6−26 inches (15−66 cm) deep. Plant foods consumed by gadwalls are lower in protein and energy and higher in fiber than the seeds and animal foods eaten by other ducks. Be­cause gadwalls rely on low-quality foods, they feed throughout the day and night. Their strategy for nu­trient acquisition is therefore more similar to that of geese than to other ducks; they consume large quantities of food to meet nutritional and energetic demands. Unlike geese, however, gadwalls do not have the capacity to store food obtained during in­termittent feeding bouts. Wintering gadwalls may be susceptible to nutritional deficiencies if continual disturbance alters their feeding regimes.
Fish and Wildlife Leaflet 13.1.2. •• 1990 5 Suggested Reading
Bellrose, F. C., editor. 1980. Ducks, geese, and swans of North America. 3rd ed. Stackpole Books, Harrisburg, Pa. 540pp.
Crabtree, R. L., L. S. Broome, and M. L. Wolfe. 1989. Effects of habitat characteristics on gadwall nest predation and nest-site selection. J. Wildl. Manage. 53:129−137.
Gates, J. M. 1962. Breeding biology of the gadwall in northern Utah. Wilson Bull. 74:43−67. Lokemoen, J. T., H. F. Duebbert, and D. E. Sharp. 1990. Homing and reproductive habits of mallards,
gadwalls, and blue-winged teal. Wildl. Monogr. 106.
28pp.
Palmer, R. S., editor. 1976. Handbook of North American birds. Vol. 2. Waterfowl. Yale University Press, New Haven, Conn. 521pp.
Paulus, S. L. 1982. Feeding ecology of gadwalls in Louisiana in winter. J. Wildl. Manage. 46:71−79.
Serie, J. R., and G. A. Swanson. 1976. Feeding ecology of breeding gadwalls on saline wetlands. J. Wildl. Manage. 40:69−81. Sugden, L. G. 1973. Feeding ecology of pintail, gadwall, American widgeon and lesser scaup ducklings in southern Alberta. Can. Wildl. Serv. Rep. Ser. 24. 44pp.
Appendix. Common and Scientific Names of Plants and Animals Named in Text.
Plants Sloughgrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Beckmannia syzigachne Coontail . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Ceratophyllum spp. Muskgrass . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Chara spp. Filamentous algae . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Chlorophyceae Fragrant flatsedge .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Cyperus odoratus Dwarfspikerush .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Eleocharis parvula Baltic rush .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Juncus balticus Redroot sedge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lachnanthes caroliniana Commonduckweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lemna minor Spikedwatermilfoil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Myriophyllum spicatum Sagopondweed .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Potamogeton pectinatus Babypondweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potamogeton pusillus Woodsrose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rosa woodsii Widgeongrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Ruppia maritima Westernsnowberry. . . . . . . . . . . . . . . . . . . . . . . . . . . . Symphoricarpos occidentalis Stingingnettle .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Urtica dioica
Birds Northernpintail .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas acuta American wigeon .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas americana Green-winged teal .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Anas crecca Mallard . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas platyrhynchos Gadwall . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Anas strepera
Invertebrates Fairy shrimp . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anostraca Midges .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .Chironomidae Waterfleas .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... Cladocera Beetles .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... ..Coleoptera Seed shrimp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . Ostracoda
UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE
Fish and Wildlife Leaflet 13
Washington, D.C.  •• 1990
6 Fish and Wildlife Leaflet 13.1.2. •• 1990 WATERFOWL MANAGEMENT HANDBOOK
13.1.3. Life History Strategies and Habitat Needs of the Northern Pintail
Leigh H. Fredrickson
Gaylord Memorial Laboratory The School of Natural Resources University of Missouri–Columbia Puxico, MO 63960
and
Mickey E. Heitmeyer
Ducks Unlimited 9823 Old Winery Place, Suite 16 Sacramento, CA 95827
The northern pintail (hereafter pintail) is a common dabbling duck distributed throughout the Northern Hemisphere. Since 1955, the breeding population in North America has averaged 5,566,000, fluctuating between 10,124,000 (1956) and 2,471,000 (1989; Fig. 1). Pintail numbers are especially sensitive to habitat conditions that reflect the wet–dry cycle in the shortgrass prairie breeding areas of south-central Canada and the northern Great Plains of the United States. Populations of pintails also are affected by habitat conditions in key wintering areas, such as the Central Valley of California and Gulf Coast marshes. When wintering areas are fairly dry, birds have fewer resources and subsequent spring recruitment is lowered.
Through the 1970’s, continental populations recovered when wetland conditions on breeding and wintering areas were good but fell when the prairies were dry and wetland conditions in wintering areas were poor. Unfortunately, habitat
Species Profile—Northern Pintail
Scientific name: Anas acuta Weight in pounds (grams):
Adults—male 2.3 (1,040 g), female 1.9 (860 g) Immatures—male 2 (910 g), female 1.8 (820 g) Age of first breeding: 1 year Clutch size: 8, range 3–14 Incubation period: 22–23 days Age at fledging: 36–43 days in Alaska, 42–57 days on prairies Nest sites: Low, sparse vegetation, often far from water Food habits: Omnivore; primarily moist-soil seeds, as well as chufa nutlets; cultivated grains, especially rice and barley. Animal foods: aquatic insects, especially chironomids, snails, terrestrial earthworms, and spiders.
losses and degradation of prairie habitats caused by agricultural practices have coincided with prolonged drought since the early 1980’s. This combination of detrimental factors resulted in declining pintail numbers in the past decade. The long-term downward trend in pintail numbers has focused renewed attention on this species.
This leaflet describes aspects of pintail life history that may be important for pintail management. It is not intended as a general reference on pintail biology. Readers interested in this should consult Bellrose (1980).
Fish and Wildlife Leaflet 13.1.3 •• 1991 1 19
55 1960 1965 1970 1975 1980 1985 1,000 8,000 6,000 4,000 2,000 0
Distribution
The northern pintail is the most widely distributed dabbling duck in the Northern Hemisphere. Although pintails regularly breed in the shortgrass prairies of the northern United States and southern Canada, their breeding distribution in North America extends from the
Fig. 1. Fluctuations in the continental population of northern pintails based on breeding population estimates, 1955–90.
Great Basin into the northern boreal forest and the arctic coastal plain of Alaska and Canada (Fig. 2).
In recent years, about 16% of the continental population of pintails (counted in May) occurred on the 26,000 square miles of high-latitude wetlands along the arctic coastal plain in Alaska. Pintails compose 90% of the dabbling ducks that use these habitats; thus, they are the most abundant dabbling duck in this region. Drakes account for about 32% of this total, whereas pairs account for
Nor
thern Pintail Breeding concentrations Winter concentrations Migration concentrations
Fig. 2. Distribution of important breeding, wintering, and migration areas for northern pintails. 2 Fish and Wildlife Leaflet 13.1.3 •• 1991 12% and groups about 57%. Pintails are well known for overflight into more northern wetland habitats when wetland habitat conditions on more southern habitats are poor; therefore, their numbers fluctuate erratically in Alaska.
Most pintails in the Pacific Flyway have traditionally wintered from the Central Valley of California to the west coast of Mexico, but the river deltas of the Pacific Northwest also provide important habitats. Large numbers of pintails also winter in coastal marshes and rice belt habitats in Texas, Louisiana, Arkansas, and the Atlantic Coast, especially South Carolina.
Spring Migration and Breeding
Pintails migrate early in spring and move northward as soon as wetlands become ice-free. They normally initiate nesting earlier in spring and summer than other dabblers (Fig. 3). These early-nesting females often encounter light snowfall while laying and incubating. Open habitats with sparse, low vegetation provide favored nesting sites. The shortgrass habitats of the Canadian prairie provinces have traditionally held the highest breeding populations. In the northern United States and southern Canada, first nests appear in early April during normal years, but inclement weather can delay nesting until the second week of May. Nesting activity in the more northern prairies peaks during the first 2 weeks of May. Pintails nest later in the boreal forest; the peak of first nests in Alaska’s interior occurs during mid-May. Birds moving to tundra habitats on the Yukon–Kuskokwim Delta and the North Slope do not nest until late May or as late as mid-June.
Pintails lay an average clutch of 8 eggs, but clutch size ranges from 3 to 14. Incubation lasts 22 or 23 days. Pintail broods can move long distances between the nest site and rearing habitats or among different brood habitats. Recent studies suggest that pintails are well adapted to making these movements and that neither mortality nor
Ju
l Aug Sep Oct Nov Dec JanFeb Mar Apr May Jun PostbreedingDispersal Molt Fall Migration Males Females Nesting Prebasic MoltSpringMigration Pairing Both Sexes
Fig. 3. The chronology of important life history events in the annual cycle of the northern pintail.
Fish and Wildlife Leaflet 13.1.3 •• 1991 3
body condition of ducklings is greatly influenced by movements of less than 3 miles. Fledging time varies with latitude and is undoubtedly influenced by the length of daylight and the daily time available to forage. Females stay with the brood until the young reach flight stage. Soon after, the female initiates the summer molt and becomes flightless (Fig. 3).
Postbreeding Dispersal and Fall Migration
Males congregate in postbreeding flocks once females begin incubation (Fig. 3). Males may move to southern or northern habitats, where they often form large aggregations and begin the Prebasic molt, becoming flightless for about 3 weeks. After regaining flight in August, they often migrate south to the ultimate wintering areas. For some pintails, the fall migration is a more gradual shift south that extends over several months. Early migrant males begin to move southward in abundance in late August or early September and usually concentrate on seasonally flooded wetlands, where they select seeds from native vegetation or from agricultural crops, especially rice.
Following brood rearing, successful females form small flocks, enter the molt, become flightless, and regrow their flight feathers in rapid succession (Fig. 3). Because males generally leave the breeding area before females are flightless, the latter use habitats distinctly different than those used by males for several months. During this time, females remain on more northern habitats and feed in semipermanent marshes, where invertebrates are important in their diet (Fig. 4). Females gradually join males on migratory and winter sites in October and November. As fall progresses, the two sexes gradually intermix and pair formation begins.
Winter Behavior and Pairing
Pintails are highly social and have loosely formed pair bonds compared to mallards and most other Northern Hemisphere dabblers. Pair formation by pintails begins on the wintering
5%
20% 15% 40% 35% 56% 77% 29% Fall Migration Winter Unpaired Winter Paired Female Prebasic (Winter) Spring Migration Prelaying Laying Postlaying Nesting Females Fig. 4. Invertebrate consumption by northern pintails during selected events in the annual cycle. Includes both sexes unless indicated otherwise. 4 Fish and Wildlife Leaflet 13.1.3 •• 1991 grounds, and most females are paired by January. Courtship flights often contain large numbers of males and traverse great distances, reach great heights, and last for extended periods. On the breeding grounds, these spectacular flights were once believed to distribute the nesting pairs widely among available habitats, but recent studies have not always confirmed this assumption—instead, they suggest active competition in mate selection and breeding opportunities among males in spring.
During winter, pintails undergo several important events in the annual cycle (Fig. 3). After completing the Prealternate molt, they form pairs; then, females initiate the Prebasic molt. By late winter and early spring, both sexes have accumulated large body fat reserves subsequently used in migration and for breeding. Females departing from the Central Valley of California to Tule Lake in late winter reach weights of 950 g, and of this total, 220 g is fat necessary to fuel migration and eventual reproduction.
Pintails are early migrants in spring and are especially attracted to large expanses of shallow open water where visibility is good and small seeds and invertebrates are readily available. Their preferred prairie nesting areas are short grasses where temporary ponds are abundant nearby.
Nesting habitat requirements in boreal forest and tundra habitats are less well known.
Foraging Ecology
Pintails are opportunistic omnivores. They primarily consume small seeds, but underground plant parts or small tubers, such as chufa nutlets, also are important (Table 1). If available, native foods are predominant in the diet, especially those associated with moist-soil habitats, including millet, smartweed, bulrush, toothcup, panicum, and swamp timothy. Pintails also exploit seeds and tubers of aquatic pondweeds and bulrushes. Although they consume seeds of all sizes, they are particularly adept at harvesting smaller seeds such as toothcup, panicum, swamp timothy, and sprangletop. These native foods provide a well-balanced diet to meet nutritional needs (Table 2). Favored cereal grains include rice and barley; pintails are less likely to eat corn than are mallards.
Animal foods are important throughout the life cycle but particularly so during molt and egg laying (Fig. 4). Some of the more important invertebrates
Table 1. Foods appearing in northern pintail diets during different events in the annual cycle.
Fall Winter Food migration Unpaired Paired
Prebasic Spring Summer Fall molt migration Nesting Ducklings molt staging
Plant Millet ++ ++ ++ Swamp timothy ++ ++ ++ Smartweed ++ ++ ++ Sprangletop + ++ ++ Toothcup + ++ ++ Curly dock +Panicum ++ ++ ++ Bulrush ++ + +Chufa + ++ ++ Pondweeds +Sedges + Agricultural grains ++ ++ ++
++ ++ + + ++ ++ ++ + + ++ ++ + + ++ + + + + ++ ++ + + + + ++ ++ ++ ++ ++ + ++ ++ ++ ++ ++ ++ + ++ ++ + + ++
Animal Chironomids ++ ++ ++ Snails ++ Odonates + Ostracods
++ ++ ++ ++ ++ ++ ++ + ++ ++ ++ + + +
Fish and Wildlife Leaflet 13.1.3 •• 1991
5 consistently appearing in the diet are snails and chironomids. Chironomids, especially, are preferred by pintails and are extremely abundant on emergence from shallow wetlands immediately after ice-out. The arrival of pintails on many migration and breeding habitats tends to coincide with this period of emergence, and pintails forage voraciously on chironomids in such newly thawed wetlands.
Pintails strip seeds from the culms of native vegetation before seeds drop in fall. Once seeds have dropped onto the substrates, pintails dabble for these foods in shallow water (4 to 6 inches). As water deepens, pintails forage by upending, but this mode of feeding is restricted to waters <18 inches deep. Pintails have a tendency to avoid areas that are flooded too deeply if shallow sites also are present.
Habitat Management
Migration and Winter
Pintails are noted for their use of large expanses of shallow, open habitats. These wetlands
often provide an abundance of food and good visibility for avoidance of predators and other disturbances during the day. At night, habitats with greater, robust cover are often sought. Although they forage in openings in southern hardwoods, pintails generally do not use flooded sites in the forest interior. Similarly, they are less apt to use woody riparian corridors than are mallards or wood ducks.
Many well-managed wetlands have the potential to provide an abundant supply of high-energy and nutritionally complete foods for pintails when water depths are <18 inches and preferably <6 inches. Gradual flooding and draining of impoundments at appropriate times during spring and fall migration create conditions that allow optimal foraging opportunities over extended periods. When impoundments vary in depth by more than 18 inches, gradual flooding increases the potential for pintails to consume more available seeds. Waters >18 inches can still provide important roost sites and give security from predators. Newly developed wetland areas are more easily managed for pintails if levees and other water control structures are configured to provide the maximum area in optimal foraging depths of ≤18 inches.
Table 2. Nutritional valuesa of some important foods consumed by northern pintails.
Plant foods
Energy kcal/g Gross Metabolized
Fat
Fiber
Percent Ash
NFEb
Protein
Nodding smartweed
4.6
—
2.7
22.0
7.5
—
9.7
Big-seeded smartweed
4.3
1.1
2.6
19.1
3.8
67.3
10.6
Wild millet
3.9
—
2.4
23.1
18.0
40.5
9.1
Walter’s millet
4.5
2.8
3.9
13.7
5.8
55.7
16.8
Sticktights
5.0
—
13.2
20.9
8.9
27.5
23.1
Rice cutgrass
3.9
3.0
2.0
10.6
9.3
57.8
12.0
Fall panicum
4.0
—
6.1
16.8
16.1
50.1
12.0
Hairy crabgrass
4.4
—
3.0
11.1
9.7
59.4
12.6
Redrooted sedge
5.2
—
—
—
—
—
—
Curly dock
4.3
—
1.2
20.4
6.9
—
10.4
Bulrush
3.5
0.8
3.0
23.6
4.3
59.1
7.2
Pondweed
3.9
0.4
2.1
20.6
15.0
50.6
14.0
Chufa seeds
—
—
22.0
5.6
5.1
58.9
8.4
Chufa tubers
4.3
—
10.6
7.3
3.1
57.1
7.0
Barley
—
2.9
2.1
7.1
3.1
—
20.0
Rice
—
2.3
9.3
11.4
9.7
73.5
10.8
Corn
4.4
3.7
4.0
2.3
1.5
77.4
11.6
aValues are averages calculated from published information. Because of wide variation in values for some seeds and inconsistency in sample sizes for each nutrient, the sum of values may not be 100%.
bNFE = Nitrogen-free extract (highly digestible carbohydrates)
6 Fish and Wildlife Leaflet 13.1.3 •• 1991 Because waste grains from agricultural Summary production are of great importance to pintails, refuge or farm programs that make these grains
available after harvest have special value for pintails in certain areas. Pintail use is increased by shallow flooding of any crop or by manipulating rice stubble by rolling or burning. Barley and rice usually are preferred over corn, although corn is consumed extensively in some locations such as the Sacramento–San Joaquin Delta of California. Maintaining ideal foraging conditions throughout winter and during spring migration provides required resources for molt, migration, and deposition of reserves for breeding. Stable water levels are undesirable, but gradual drawdowns have the potential to increase the vulnerability of invertebrate prey and to make seeds within mud substrates accessible. Furthermore, some good foraging sites should be protected from disturbance by hunters, bird watchers, aircraft, and boaters, as well as from management activities throughout fall and winter.
Breeding
The highest nesting densities occur in open habitats where vegetation is low and sparse. Common plants in these locations include prairie grasses, whitetop, nettle, spike rush, rushes, and buckbrush. Pintails nest in agricultural lands more frequently than other dabblers and readily use pastures, stubble fields, roadsides, hayfields, fallow fields, and the edges or margins around grain fields. In the boreal forest, nesting is concentrated on more open areas with sedge or grass meadows.
Establishment of tall, dense cover is a common practice to provide nesting sites for some dabblers. This practice is less valuable for pintails because they prefer sparser cover for nesting. Grazing programs that leave good residue ground cover but remove robust growth can enhance nesting cover for pintails. Well-conceived farm programs that protect habitats and ephemeral wetlands are especially important for breeding pintails. Because pintails regularly nest in agricultural lands, programs that provide benefits to farmers for delaying haying or for protecting nesting cover surrounding wetlands have the greatest potential to increase pintail recruitment.
Pintails offer a great challenge to waterfowl managers because they associate with many habitats that are used intensively by agricultural interests. Their preference for open areas and small, shallow wetlands in areas with little rainfall and recurring droughts puts a large part of their breeding area in jeopardy regarding consistent conditions. Developing farm programs compatible with pintail life history requirements offers the greatest opportunities for habitat enhancement, and therefore population recoveries by pintails on the prairies. Northern boreal and tundra habitats must be protected from loss or degradation.
Adequate migration and wintering habitats must be protected, restored, and enhanced. This will require continued acquisitions or other means of protection of key habitats and more effective management of public and private wetlands. One of the greatest opportunities to enhance wintering and migration habitats is to identify scenarios that will benefit rice culture and simultaneously provide needed resources for pintails. This adaptable, highly mobile species has a history of responding rapidly to good habitat conditions across the continent. By providing these habitats to pintails, we can assure their survival and abundance in the future.
Suggested Reading
Bellrose, F. C., editor. 1980. Ducks, geese, and swans of North America. 3rd ed. Stackpole Books, Harrisburg, Penn. 540 pp.
Fredrickson, L. H., and F. A. Reid. 1988. Nutritional values of waterfowl foods. U.S. Fish Wildl. Serv., Fish Wildl. Leafl. 13.1.1. 6 pp.
Krapu, G. L., and G. A. Swanson. 1975. Some nutritional aspects of reproduction in prairie nesting pintails. J. Wildl. Manage. 39:156–162.
Miller, M. R. 1986. Northern pintail body condition during wet and dry winters in the Sacramento Valley, California. J. Wildl. Manage. 50:189–198.
Raveling, D. G., and M. E. Heitmeyer. 1989. Relationships of population size and recruitment of pintails to habitat conditions and harvest. J. Wildl. Manage. 53:1088–1103.
Note: Use of trade names does not imply U.S. Government endorsement of commercial products.
Fish and Wildlife Leaflet 13.1.3 •• 1991 7 Appendix. Common and Scientific Names of Plants and Animals Named in Text.
Plants
Toothcup or Ammania
Ammania coccinea
Sticktights
Bidens sp.
Sedges
Carex spp.
Redroot flatsedge
Cyperus erythrorhizos
Chufa flatsedge
Cyperus esculentus
Hairy crabgrass
Digitaria sanguinalis
Japanese millet
Echinochloa crusgalli
Walter’s millet or wild millet
Echinochloa walteri
Spike rush
Eleocharis sp.
Swamp timothy
Heleochloa schoenoides
Barley
Hordeum vulgare
Rush
Juncus sp.
Rice cutgrass
Leersia oryzoides
Sprangletop
Leptochloa spp.
Rice (cultivated)
Oryza sativa
Panicum or panic grass
Panicum spp.
Nodding smartweed or smartweed
Polygonum lapathifolium
Big-seeded smartweed or Pennsylvania smartweed
Polygonum pensylvanicum
Pondweeds
Potamogeton spp.
Curly dock
Rumex spp.
Bulrush
Scirpus sp.
Whitetop
Scolochloa festucacea
Buckbrush or snowberry
Symphoricarpos spp.
Nettle
Urtica spp.
Corn or Indian corn
Zea mays
Birds
Wood duck
Aix sponsa
Northern pintail
Anas acuta
Mallard
Anas platyrhynchos
Invertebrates (Families)
Chironomids
Chironomidae
Earthworms
Lumbricidae
UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE
Fish and Wildlife Leaflet 13
Washington, D.C. •• 1991
8
WATERFOWL MANAGEMENT HANDBOOK
13.1.6. Life History and Habitat Needs of the Wood Duck
Katie M. Dugger
Gaylord Memorial Laboratory The School of Natural Resources University of Missouri—Columbia Puxico, Missouri 63960
and
Leigh H. Fredrickson
Gaylord Memorial Laboratory The School of Natural Resources University of Missouri—Columbia Puxico, Missouri 63960
The wood duck is North America’s most widely distributed endemic species, and most of its wintering and breeding range falls within the 48 contiguous states (Fig. 1). The wood duck inhabits forested wetlands and, because of its need for nest cavities, is closely tied to North America’s remaining forest resources. Habitat destruction, market hunting, and liberal hunting seasons contributed to drastic declines and, in some cases, regional eradication of local wood duck populations. Subsequent implementation of hunting restrictions and the high reproductive rate of the species are responsible for the recovery of wood duck populations to current stable levels.
As prairie duck populations continue to decline, hunting pressure on the wood duck continues to increase. The wood duck is popular with hunters and consistently ranks high among species in Atlantic and Mississippi flyway duck harvests.
Species Profile—Wood Duck
Scientific name: Aix sponsa Weight in pounds (grams):
Adults—male 1.5 (682), female 1.5 (673) Immatures—male 1.5 (668), female 1.4 (614) Age at first breeding: 1 year Clutch size: 12, normal range 7−15 Incubation period: 30 days, range 26−37 Age at fledging: 56−70 days Nest sites: Tree cavities or artificial nest boxes
within about 0.6 mi (1 km) of water.
Food habits: Omnivorous. Plant foods include primarily acorns, maple samaras, elm seeds, and moist-soil plant seeds. Animal foods consist mainly of aquatic-associated and nonaquatic insects, but also some aquatic invertebrates.
Harvest pressure and continued degradation of riparian and lowland hardwood forests increases the need for a thorough understanding of wood duck population dynamics. Equally important to sustaining current wood duck population levels is an understanding of annual life cycle events and requirements.
Distribution
Three distinct wood duck populations occur in North America: the Atlantic, Interior, and Pacific. The Atlantic population includes states of the
Fish and Wildlife Leaflet 13.1.6. •• 1992 1 Fig. 1. Current wood duck breeding distribution (after Fredrickson et al. 1990).
Atlantic Flyway and southeastern Canada, the extreme northern range of the wood duck. The Interior population includes wood ducks throughout the Mississippi Flyway, part of Ontario, and the eastern tier of states in the Central Flyway. Historically, the Rocky Mountains and treeless portions of the Great Plains created a discontinuity between the Interior and Pacific populations. As woody riparian corridors developed in the plains, a westward expansion by breeding wood ducks occurred throughout the Great Plains states after the 1960’s (Fig. 1). Currently, northern portions of the Pacific and Interior populations are contiguous. The Pacific population ranges principally from British Columbia southward into Washington, Oregon, California, northwestern Idaho, and western Montana, but small numbers of breeding wood ducks are also present in Nevada, Utah, New Mexico, and Arizona. Wood ducks breed throughout most of their range but are at particularly high breeding densities in the Mississippi alluvial valley (Fig. 1). Wintering wood ducks use the more southern habitats throughout their range; habitats of greatest importance include California’s Central Valley and the southern states of the Mississippi and Atlantic flyways (Fig. 2).
Population Status and Harvest
Traditional aerial census techniques are ineffective in forested habitats; thus, the current status of wood duck populations can only be approximated.
The average annual wood duck harvest before 1963 was <165,000 birds, but during 1980−1989, an annual average of 1,067,000 wood ducks was harvested in the United States (Frank Bellrose, personal communication). While the dramatic increase in wood duck harvest levels since the 1960’s can be attributed to an overall increase in the continental wood duck population, the interactions between wood duck population
Fig. 2. Wood duck winter distribution (after Bellrose 1980).
2 Fish and Wildlife Leaflet 13.1.6. •• 1992 dynamics and harvest levels is poorly understood. Current research and historic events suggest harvest regulations can have an effect on wood duck populations in some situations. For example, female wood ducks breeding in northern areas are extremely susceptible to hunting during early seasons that open before the onset of migration. In addition, northern birds are subjected to continued harvest pressure as they migrate southward to winter because waterfowl hunting seasons open in succession from north to south.
Spring Migration and Breeding
In southern regions, wood ducks breed and winter in essentially the same areas. Birds that nest farther north begin northward movements in late winter. Wood duck nests are initiated as early as late January in the South, early March in the Midwest, and mid March to early April in the North. Migrating female wood ducks lack the fat and protein reserves necessary for egg production when they arrive on the breeding grounds. Therefore, upon arrival, wood duck pairs disperse into forested and riparian habitats where females forage intensively in preparation for egg laying.
During this time, nesting pairs also begin searching for suitable cavities, primarily in tracts of forest adjacent to important waterways. Although natural cavities within 0.3 mile (0.5 km) of water and near forest canopy openings are preferred, wood ducks will nest ≥0.6 mile (1 km) from water when necessary. The availability of suitable cavities varies within the wood duck’s range (Table 1) because some tree species develop cavities more readily than others. Large trees, ≥12 inches (30 cm) dbh (diameter breast height), produce the most important cavities for wood ducks. Cavities with an entrance size of ≥3.5 inches
(8.9 cm), an interior basal area of ≥40 square inches (258 cm2), and height ≥6 feet (2 m) above the ground are preferred for nesting.
Average clutch size is 12 eggs, but more than one female may contribute to a clutch (dump nest), which can result in clutches of more than 60 eggs. These huge clutches are rarely incubated, but successful dump nests of less than 30 eggs are common in nest boxes. A wood duck clutch is incubated for an average of 30 days at middle latitudes and a few days less in the South.
Female wood ducks and their broods are highly mobile. Initial movements by broods after leaving a nest can be up to 2.4 miles (4 km) but average 0.8 mile (1.3 km), mostly along waterways. Shallowly flooded habitat with good understory cover, such as shrub−scrub or emergent vegetation, is the most important habitat for wood duck broods. Duckling survival ranges from 36 to 65% with most mortality (86−91%) occurring the first week after hatching. Common duckling predators include mink, raccoon, snapping turtle, bullfrog, largemouth bass, and other large predatory fishes.
The bond between the female and her brood begins to weaken after about 4 weeks; ducklings fledge between 6 and 8 weeks. Some early-nesting
Table 1. Nest cavity density in some North American tree species.
Cavity density Location Species Number/acre Number/hectare
Southeastern Missouri Blackgum, green ash, pumpkin ash, red maple 0.13 0.33 Illinois Black oak, bitternut hickory, mockernut hickory, 0.21 0.51
blackjack oak, red oak, American elm, hackberry Massachusetts Apple, ash, maple — — New Brunswick Silver maple, American elm 2.23 5.50 Indiana American beech, American sycamore, red maple 0.50 1.23 Minnesota Quaking aspen, American elm, sugar maple, basswood 1.70 4.20 Wisconsin Silver maple, sugar maple, basswood, quaking aspen 0.26 0.65 Mississippi American sycamore, American beech, blackgum, 0.08 0.19
shagbark hickory, water oak, cherrybark oak
Overcup oak, slippery elm, sugarberry 0.09
0.23
Fish and Wildlife Leaflet 13.1.6. •• 1992 3 females in southern latitudes renest, successfully producing two broods before finishing the Prebasic molt (Table 2). Females begin the Prebasic molt in early spring, but it is interrupted during nesting and is not completed until late summer (Fig. 3), when the females regain their flight feathers. Conversely, males may acquire their eclipse plumage as early as mid-May. After the female begins incubation, the male wood duck begins the Prebasic molt and becomes flightless about 3 weeks later. After regaining flight (in about 22 days), the male begins the Prealternate molt and returns to Alternate plumage by late summer.
Post-breeding Dispersal and Fall Migration
After completing the Prebasic molt and before southward migration begins, adult and immature males, as well as some immature females, disperse radially from their breeding and natal areas into new habitats. At southern latitudes, this dispersal tends to be lateral, but in central and northern regions, northward dispersal is most common. In late September, wood ducks begin migrating south. During peak migration in October and November, wood duck numbers fluctuate erratically at migration stopovers where they form large roosting flocks (>100 birds). On the wintering grounds, smaller groups (<30 birds) are more common.
Behavior and Pairing
Wood ducks begin courting before fall migration. Courting activity drops off during harsh weather in winter and resumes in spring. Courtship activity is more intense in fall than in spring; courting parties are larger and displays are longer and more frequent. Wood ducks breed as yearlings, but evidence suggests that only about 40% of the surviving yearling females nest each season. Yearling females produce smaller clutches and fledge fewer young than experienced nesters. The productivity of young male wood ducks may also be low. When compared with adult drakes, yearling males do not perform courtship displays with the proper orientation and timing. Thus, early pairing by inexperienced males is unlikely.
Table 2. Length of breeding season and frequency of double brooding in wood ducks.
Mean length
Double-
Mean interval
of breeding
Captured
brooding
between
season
females
females
clutches
Location
(days)
(n)
(%)
(days)
Alabama
159
231
9.2
37
South Carolina
157
275
7.6
47
California
134
1,540
3.6
26 ± 1.7
Missouri
132
924
2.2
33 ± 1.8
Massachusetts
95
—
—
—
Foraging Ecology
Food habits of adult wood ducks are sex related and seasonally driven (Fig. 4). During winter, nearly 100% of the diet of wood ducks consists of plant foods, of which 75% may be acorns. An increase in animal foods in the diet (to about 35%) occurs in both sexes in early spring. This percentage remains constant for the male wood duck through summer and fall while undergoing the Prebasic and Prealternate molts, but increases to about 80% for the female during egg laying. Female wood ducks increase the amount of invertebrates in the diet to meet daily protein needs during egg laying. After egg-laying, animal foods compose less of the female’s diet, while consumption of high-energy seeds increases to meet the daily dietary requirements of incubation (Fig. 4).
Wood ducks consume a variety of plant and animal foods (see Appendix), typically by pecking or dabbling at foods on the surface. Subsurface and bottom feeding are rare. Therefore, shallow depths are important to make food available to foraging wood ducks. Because wood ducks feed mainly on the surface or at the edge of wetlands, nonaquatic and aquatic-associated invertebrates make up a large percentage of the invertebrates consumed. Live-forest and emergent vegetation are common wood duck foraging habitats. Wood ducks do not forage readily in agricultural fields unless shallowly flooded, live-forest habitats are not available.
Habitat Management
The wood duck carries out its entire annual cycle within a forested wetland complex, including a mixture of habitats such as live forest, greentree
4 Fish and Wildlife Leaflet 13.1.6. •• 1992 reservoirs, rivers, oxbows, riparian corridors, beaver ponds, shrub−scrub, and robust emergent vegetation. Such habitats have been destroyed or modified across the continent. For example, only 17% of the original forest acreage remains in the Mississippi alluvial valley today. In addition, certain management practices have detrimental effects on tree vigor and mast production. Flooding before fall senescence or beyond dormancy into the growing season reduces mast production, causes
Fig. 3. The chronology of important life history events in the annual cycle of the wood duck.
tree damage, and may eventually kill trees. Improper flooding regimes change tree species composition in a stand from desirable oak species that produce small acorns, easily eaten by waterfowl, to the more water-tolerant overcup oak, which produces very large acorns that are unsuitable for waterfowl food. Water depths ≤8 inches (20 cm) are ideal for foraging wood ducks, while loafing and roosting sites can be maintained where water levels are higher.
Fig. 4. Proportion of plant (open) and animal (dark) foods consumed by wood ducks throughout their annual cycle.
Fish and Wildlife Leaflet 13.1.6. •• 1992 5 Timber management within greentree reservoirs and naturally flooded forests is an important component of habitat management for wood ducks. Most timber harvest practices remove large, overmature trees, the primary source of wood duck nest cavities. Although selective thinning within a stand promotes regeneration of desirable shade-intolerant red oak species, some large and overmature trees should be preserved as potential wood duck nest sites. In addition, a mix of species within a stand should be encouraged because desirable mast species may not form cavities. Elm and maple are important components of most wood duck habitat because they provide protein-rich samaras in spring and suitable nest cavities (Table 1).
Nest boxes are a useful management tool where natural cavities are scarce but good brood habitat is available. Currently, nest box management may contribute approximately 150,000 juvenile wood ducks to fall flights in the Mississippi and Atlantic flyways. Although this constitutes only a small portion of the juvenile component in the eastern fall flight, nest boxes, when properly erected and maintained, can substantially increase local populations.
Wood ducks will readily nest in boxes constructed of wood, metal, or plastic. Rough-cut cypress boxes are durable, economical, and blend well with the environment within a few years. Although plastic and metal boxes are durable, internal temperatures of boxes placed in the direct sun in the South are high enough to kill developing embryos.
Whatever the construction material, boxes must be predator-proof. Inverted conical shields or smooth, wide pieces of metal wrapped around the pole or tree beneath a box can keep raccoons and some snakes from entering boxes. Predation can also be discouraged by placing boxes on poles over water or by mounting boxes on bent metal brackets that suspend them 2 feet (0.6 m) from a tree or post.
Annual maintenance and repair of boxes is necessary for continued use by wood ducks. Boxes with unsuccessful nests are unavailable for use until debris from the nest is removed. The frequency of box checks necessary for maintenance depends on climatic conditions and the types of use boxes receive during winter (e.g., screech-owl roosts, squirrel or raccoon dens).
Number and placement patterns of nest boxes within habitats influence box use, nest success, and dump-nesting rates. When box management began 50 years ago, some local wood duck populations were small, and box use was higher when boxes were placed in highly visible, clumped arrangements rather than as widely spaced single units. As wood duck populations grew, high dump-nesting rates, nesting interference, and overall decreases in production occurred. In some situations, single, well-spaced boxes may decrease dump-nesting and nesting interference; however, in prime wood duck breeding habitats hidden boxes simply require more effort to maintain. Boxes acceptable to nesting wood ducks must also be accessible to managers for maintenance and data collection. Although wood duck boxes can increase local production, the preservation of bottomland hardwoods and proper water and timber management in these habitats are paramount to the continued success of continental wood duck populations.
Summary
Although current wood duck populations are stable, continued preservation and proper management of bottomland hardwood and riparian forest resources are imperative. Wood duck population estimates are inaccurate; hence, managers have little knowledge about population cycles or the effect of increased hunting pressure on the continental population. Moreover, protecting North America’s remaining forest resources in the face of increasing agricultural and commercial development remains difficult. In particular, forest resources in the lower Mississippi alluvial valley must be carefully preserved and managed to continue providing wintering habitat for a large percentage of the continental wood duck and mallard populations.
At the local level, wood duck populations can be boosted by production from nest boxes, but more information is needed on the density-dependent effects of box placement on nesting interference. Nest box maintenance can be expensive and time consuming. Thus, management for natural cavities should be encouraged. Flooding of greentree reservoirs should simulate natural hydrology and reflect wood duck water depth needs. Remaining forested habitats should be protected and maintained in the best possible condition to sustain larger numbers of birds throughout their annual cycle as high quality habitat continues to disappear.
Fish and Wildlife Leaflet 13.1.6. •• 1992 6
Suggested Reading
Bellrose, F. C. 1980. Ducks, geese and swans of North America. Third ed. Stackpole Books, Harrisburg, Penn. 540 pp.
Delnicke, D., and K. J. Reinecke. 1986. Mid-winter food use and body weights of mallards and wood ducks in Mississippi. Journal of Wildlife Management 50:43−51.
Fredrickson, L. H., G. V. Burger, S. P. Havera, D. A. Graber, R. E. Kirby, and T. S. Taylor, editors. 1990.
Proceedings of the 1988 North American Wood Duck Symposium, St. Louis, Mo. 390 pp.
Grice, D., and J. P. Rogers. 1965. The wood duck in Massachusetts. Massachusetts Division of Fish and Game, Final Report Federal Aid in Wildlife Restoration Project W-19-R. 96 pp.
Trefethen, J. B., editor. 1966. Wood duck management and research: a symposium. Wildlife Management Institute, Washington, D.C. 212 pp.
Appendix. Common and Scientific Names of Plants and Animals Named in Text.
Plants
Red maple . . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . .. . . .. . . .. Acer rubrum Silver maple . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . Acer saccharinum Sugarmaple . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . . . . . . . . . . . . . Acer saccharum *Maple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acer spp. *Asiaticdayflower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aneilema keisak *Beggarticks . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . .. Bidens spp. *Watershield . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . .. Brassenia schreberi Bitternuthickory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carya cordiformis Shagbark hickory . . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . .. . . .. Carya ovata Mockernuthickory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carya tomentosa Sugarberry . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Celtis laevigata Hackberry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Celtis occidentalis *Buttonbush . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . .. Cephalanthus occidentalis *Barnyardgrass ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Echinochloa crusgalli *Barnyardgrass ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Echinochloa muricata Americanbeech .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . Fagus grandifolia Green ash .. . ... . ... . ... . ... . ... . ... . ... . ... . ... . . .. . ... Fraxinus pennsylvanica *Ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fraxinus spp. Pumpkinash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fraxinus tomentosa *Soybeans .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. Glycine max *St. John’s-wort ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . .. Hypericum walteri *Ricecutgrass . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... Leersia oryzoides *Sweetgum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquidambar stryraciflua *Primrosewillow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ludwigia leptocarpa *Watermilfoil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Myriophyllum pinnatum *Whitewaterlily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nymphaea odorata Blackgum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nyssa sylvatica *Panicgrasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panicum spp. *Floating paspalum . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . .. Paspalum fruitans Americansycamore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Platanus occidentalis *Smartweeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polygonum spp. Quaking aspen ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . . Populus tremuloides *Pondweeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potamogeton spp. Apple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pyrus malus Cherrybarkoak ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Quercus falcata Overcupoak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus lyrata Blackjack oak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus marilandica *Wateroak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus nigra *Nuttalloak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus nuttallii *Pinoak . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . Quercus palustris *Willow oak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus phellos Red oak ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Quercus rubra *Postoak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus stellata Oak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus spp.
Fish and Wildlife Leaflet 13.1.6. •• 1992 7 Black oak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quercus velutina *Blackberry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rubus cuneifolius *Sassafras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sassafras albidum *Slough grass . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... Sclera reticularis *Bigduckweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spirodela polyrrhiza *Baldcypress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taxodium distichum Basswood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tilia americana Americanelm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ulmus americana Slipperyelm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ulmus rubra Elm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ulmus spp. Black haw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Viburnum prunifolium Grapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vitus spp.
Vertebrates Woodduck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aix sponsa Mallard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anas platyrhynchos Snappingturtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chelydra serpentina Largemouthbass . . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . . Micropterus salmoides Mink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mustela vison Screech-owl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Otus spp. Raccoon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Procyon lotor Bullfrog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rana catesbeiana
Invertebrate taxa *Spiders ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Araneida *Crayfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Astacidae *Midges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chironomidae *Water boatmen ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Corixidae *Scuds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gammarus sp. *Whirligig beetles . . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . .. . . .. . . Gyrinidae *Sowbugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isopoda *Back swimmers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Notonectidae *Damselflies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Odonata *Dragonflies . . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . ... . Odonata *Orbsnails . . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . . . . . .. . . .. . . .. Planorbis sp. *Caddisflies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trichoptera
*Common wood duck foods.
Note: Use of trade names does not imply U.S. Government endorsement of commercial products.
UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE
Fish and Wildlife Leaflet 13
Washington, D.C. •• 1992
8
WATERFOWL MANAGEMENT HANDBOOK
U.S. DEPARTMENT OF THE INTERIOR NATIONAL BIOLOGICAL SERVICE WATERFOWL MANAGEMENT HANDBOOK 13
13.1.8. Life History and Management of the Blue-winged Teal
James H. Gammonley
Colorado Division of Wildlife 317 W. Prospect Road Fort Collins, CO 80526
and
Leigh H. Fredrickson
Gaylord Memorial Laboratory The School of Natural Resources University of Missouri-Columbia Puxico, MO 63960
The blue-winged teal is a small dabbling duck that is common in North America and northern South America. The species is highly mobile and has an opportunistic life history strategy. Breeding populations respond to variable wetland conditions in the drought-prone prairie regions of the north-central United States and southern Canada. Extensive habitat loss and degradation has occurred on the prairies and on neotropical wintering areas in recent decades. Renewed interest in the ecology and management of blue-winged teal has resulted from these environmental pressures. We review life history characteristics of blue-winged teal that are important to managers. Readers should consult Bennett (1938) and Bellrose (1980) for general references on the biology of blue-winged teal.
Species Profile—Blue-winged Teal
Scientific Name: Anas discors Weight in pounds (grams):
Adults—male 1.0 (454), female 0.9 (410)
Immatures—male 1.0 (454), female 0.9 (410)
Age at first breeding: 1 year
Clutch size: 10, range 6 to 15
Incubation period: 23 days
Age at fledging: 35−44 days
Nest sites: Herbaceous vegetation, primarily grasses and sedge meadows, at variable distances from water up to 1 mile (1.6 km)
Food habits: Omnivorous; plant foods include vegetative parts of duckweeds, coontail, muskgrass and pondweeds, and seeds of bulrushes, sedges, spikerushes, water lilies, and grasses. Animal foods predominate in diet during breeding and include snails, aquatic insects, fairy shrimp, and crustaceans
Distribution
Blue-winged teal concentrate breeding in the Prairie Pothole Region (PPR) of the north-central United States and southern Canada (Fig. 1). Breeding pairs are especially abundant in mixed-prairie grasslands of North and South Dakota and southern Canada, and highest densities occur in southwestern Manitoba. The proportion of blue-winged teal breeding in the PPR
Waterfowl Management Handbook 13.1.8. •• 1995
1 Fig. 1. Breeding, wintering, and migration areas for blue-winged teal.
is correlated with annual numbers of ponds in May. Blue-winged teal are also common in parts of the northeastern United States and the Great Lakes region. Few blue-winged teal nest in northern boreal forest or arctic habitats, although some birds are displaced to these areas when drought conditions occur in the PPR. Significant breeding populations also occur in Kansas and Nebraska, and blue-winged teal regularly breed along the Gulf Coast of the United States. Blue-winged teal are largely replaced by the cinnamon teal in the Great Basin and western intermountain regions, but small breeding populations are present.
Blue-winged teal winter farther south than other ducks that breed in North America. Major wintering concentrations occur along the Gulf Coast of Mexico and in Caribbean coastal areas of Venezuela, Colombia, and Guyana (Fig. 1). In these areas, blue-winged teal occupy coastal lagoons and lowland marshes, as well as large interior wetland systems. In recent decades, large numbers of blue-winged teal have wintered along the Gulf Coast of the United States.
Spring Migration and Breeding
Blue-winged teal are one of the last species of ducks to arrive on northern breeding areas. Those wintering in South America begin moving north through Mexico in January, but the majority of spring migrants does not arrive on prairie breeding areas until late April or May (Fig. 2). Courtship occurs on wintering areas and continues during spring migration, and most blue-winged teal are paired before arrival at the nesting location. Nest initiation begins shortly after arrival; peak nesting usually occurs in late May in the United States and in early June in Canada. Most yearling females nest.
Blue-winged teal have low rates of breeding philopatry when compared with other dabbling ducks. Females change breeding sites from year to year in response to changes in wetland conditions. When habitat conditions in the PPR are unfavorable, large portions of the breeding population may occupy other parts of the breeding range. Males defend discrete breeding territories, usually consisting of one or two small ponds within the home range. Breeding pairs prefer shallowly flooded temporary and seasonal wetlands, and pair densities are correlated with densities of flooded wetland basins. In years when temporary and seasonal wetlands are dry, gently sloping semipermanent basins that provide shallow water are important.
Typically, nests are located in upland grasses or wet meadow sedges. Nest cover is provided by matted residual herbacous vegetation. Nests usually are located near water, but may be as far as 1 mile (1.6 km) from the nearest wetland. Cereal grain and forage production and livestock grazing limit available nesting cover throughout the prairie region, although alfalfa and bluegrass in cultivated or grazed areas can provide suitable nesting cover. Blue-winged teal seem to prefer to nest in native grass communities in good range condition. Success of breeding pairs is higher in native plant communities than in exotic vegetation communities.
Clutch size ranges from 6 to 15 eggs, and averages 10. Females incubate for 23 days. As with most upland-nesting ducks in the PPR, large numbers of nests are lost to mammalian and avian predators. Nests in hay fields (e.g., alfalfa) often are destroyed during harvest. Females commonly
Waterfowl Management Handbook 13.1.8. •• 1995 2
renest if nest loss occurs early in laying, but hens that lose clutches during incubation are less likely to renest. Renesting, even by hens losing clutches late in incubation, is more likely to occur when wetland conditions are good.
Semipermanent wetlands located near nests are important habitats for broods. Stock ponds with well-developed emergent vegetation provide locally important brood habitat. Seasonal wetlands also provide excellent brood habitat, but because blue-winged teal are relatively late nesters, seasonal wet­lands are often unavailable when ducklings leave nests. Females lead newly hatched ducklings over­land to wetlands with suitable brood habitat. Broods are more active and more easily observed in early morning and late afternoon. Most duckling mortality occurs within the first 14 days after hatch. Young are able to fly at 35−44 days of age.
Postbreeding Dispersal and Fall Migration
Males leave breeding territories 2 to 3 weeks after incubation begins to molt (Fig. 2). Males form groups on some breeding areas during molt, or congregate in large flocks of hundreds or thousands on large marshes away from areas used during
Fig. 2. Important life history events in the annual cycle of the blue-winged teal.
breeding. Males remain flightless for 26−36 days, feed at night, and conceal themselves in wetland vegetation during the day. Females begin wing molt after young are fledged, although some females may initiate molt in late stages of brood-rearing.
Blue-winged teal begin fall migration earlier than most other duck species. Upon regaining flight in mid- to late August, males begin moving southward in small groups. Males begin the prealternate molt in early fall, but often lack their characteristic white facial crescent during migration (Fig. 2). Successfully breeding females migrate after most males, and by late September migrating flocks are comprised primarily of adult females and immatures (Fig. 2). Most migrant blue-winged teal arrive at wintering areas along the U.S. Gulf Coast by late summer. Large numbers move through Mexico in August, and most continue on to wintering areas in Central and South America.
Winter
As on breeding areas, winter distribution is variable in response to habitat conditions. Standardized counts of wintering populations in Central and South America are lacking. In some
Waterfowl Management Handbook 13.1.8. •• 1995 3
years, relatively large numbers remain on the lagoons and marshes of the Gulf Coast of Mexico (Tabasco and Yucatan). January surveys of wetlands in Mexico show wide fluctuations in numbers of blue-winged teal, due to annual differences in the chronology of spring migration from South American wintering areas. Blue-winged teal also pioneer into new winter habitats; after hurricanes opened marshes along the U.S. Gulf Coast in the 1950s, many thousands of teal began wintering in these habitats far north of traditional wintering sites.
Feeding
Blue-winged teal are omnivorous, and usually feed in portions of wetlands that are flooded less than 8 inches (20 cm) deep. During breeding, aquatic invertebrates provide most of the protein and minerals required for egg production. Endogenous lipid reserves contribute about 40% of egg lipid requirements. Additional lipids are obtained from foods consumed on wetlands used for breeding. Blue-winged teal do not store significant nutrient reserves on wintering areas, so most lipid storage apparently occurs during spring migration.
Diverse and abundant invertebrate populations develop in temporary and seasonal wetlands and are available to teal feeding in these shallow basins. Snails, midge and mosquito larva and adults, fairy shrimp, beetles, amphipods, and isopods in these habitats are important foods for blue-winged teal during spring migration and breeding (Table). As seasonal wetlands dry over the summer, teal move to semipermanent wetlands to feed. Although diversity and availability of aquatic invertebrates is relatively low in more permanently flooded basins, emerging aquatic insects provide food for blue-winged teal in these wetlands.
During the postbreeding period, snails, midge and mosquito larva, water fleas, and amphipods were consumed by molting males on Delta Marsh in Manitoba (Table). Seeds and aquatic vegetation comprised 43% of these birds’ diets. In Texas, fall migrants primarily consumed seeds of wild millet, milo, and other plant foods (Table).
Wintering blue-winged teal spent up to 50% of daylight hours feeding on marshes along the west coast of the Yucatan Peninsula in Mexico. Small snails (98%) and widgeongrass seeds were consumed early in winter, whereas muskgrass (98%), snails, odonates, and corixids comprised diets in late winter (Table). In Costa Rica, blue-winged teal fed at night on rice seeds (92%) and insects in cultivated rice fields (Table). In Colombia, blue-winged teal fed predominantly (54%) on plant foods (primarily water lily seeds) during one year, but switched to animal-dominated
Table. Percentage of animal foods in the diet of blue-winged teal during the annual cycle.
Season and sex Animal diet (%) Location Spring migration 65 Moist-soil impoundments Both sexes Missouri Breeding season 89 Prairie wetlands Both sexes North Dakota Spring and summer 99 Prairie wetlands Laying females North Dakota Post-breeding period 57 Delta Marsh, Manitoba Males Canada Fall migration 8 Playa wetlands Both sexes Texas Early winter 98 Celestun Estuary Both sexes Mexico Late winter 2 Celestun Estuary Both sexes Mexico Winter (Dec−Feb) 8 Palo Verde refuge Both sexes Costa Rica Winter 1979−80 46 Cienaga Grande Females Colombia Winter 1985−88 73 Cienaga Grande Both sexes Colombia
4 Waterfowl Management Handbook 13.1.8. •• 1995 diets (snails, corixids, and insects) in years when water salinity increased (Table).
Population Status and Harvest Management
The target population for blue-winged teal in the North American Waterfowl Management Plan is 5,300,000 birds. Breeding population estimates have averaged 4,138,000 since 1955, ranging from 5,829,000 in 1975 to 2,776,000 in 1990 (Fig.3). These estimates are subject to considerable bias and error, however. Annual surveys are conducted in May to coincide with the peak of mallard nesting, and in some years many blue-winged teal do not arrive on surveyed areas until after counts are conducted. Furthermore, significant proportions of the blue-winged teal breeding population may occupy locations outside the surveyed area, particularly in years when habitat conditions are poor in the PPR (e.g., the 1980s).
Based on annual breeding ground estimates, blue-winged teal comprise over 14% of the continental duck population. This species is lightly hunted, averaging less than 6% of the total annual duck harvest in the United States. Because blue-winged teal migrate earlier in fall than most other North American ducks, special harvest regulations have been used in some years since the 1960s to increase hunting opportunities for teal. September teal-only seasons of up to 9 days and bonus blue-winged teal bag limits have been used in some states in the Central, Mississippi, and Atlantic flyways. When offered, the teal harvest in September has averaged 201,991 birds, or 32% of
the total blue-winged teal harvested in the United States. Most blue-winged teal are harvested in the Mississippi (61%) and Central (21%) flyways during the combined September and regular seasons. September teal seasons were suspended in 1988, but were reinstated in many states in 1992.
Harvest rates south of the United States are less well-documented. Through 1980, 21% of all reported recoveries of leg-bands from blue-winged teal were from south of the United States. Most (37%) of these recoveries were from South America, followed by Mexico (28%), the Caribbean (25%), and Central America (10%). Many bands recovered in the neotropics may go unreported, however, complicating the use of banding data to determine blue-winged teal distribution and harvest.
Relatively low harvest and band recovery rates have also limited estimates of annual survival for blue-winged teal. Available estimates are similar to but slightly lower than those reported for other dabbling ducks: adult females—0.52, adult males—0.59, juvenile females—0.32, juvenile males—0.44. Females are more vulnerable to predators than males during nesting, but do not seem to suffer significantly greater mortality than females of other dabbling duck species. Factors affecting survival rates in winter are not well known.
Habitat Management
Blue-winged teal exploit a diversity of wetland habitats to meet their nutritional and behavioral requirements during the annual cycle. During spring migration and nesting, pairs find an
Fig. 3. Estimates of the continental breeding population (millions of birds) of blue-winged teal, 1955−1994.
Waterfowl Management Handbook 13.1.8. •• 1995 5
abundance of aquatic invertebrates in highly productive temporary and seasonally flooded wetlands. Semipermanent wetlands with gently sloping basins and both emergent and submergent vegetation provide foraging and brood-rearing sites, and are very important in dry years on the drought-prone prairies. High densities of these wetland types in areas with high-quality nesting cover allow teal to establish nesting territories and avoid long overland brood movements. Restoration of temporary and seasonal wetlands is particularly needed in agricultural landscapes.
Breeding success of blue-winged teal is enhanced when extensive areas of suitable upland nesting cover are available near wetlands used by pairs and broods. In native prairie grass communities, dead vegetation should accumulate over several growing seasons to provide matted mulch used for nest sites. Periodic disturbance is required to keep grass cover from becoming too dense. Burning, mowing, and grazing can be used effectively to maintain range condition for blue-winged teal nesting. Optimal intervals between grassland disturbance are dependent upon local conditions. When possible, grassland disturbance should be performed after the peak hatching period of blue-winged teal. Seeded dense nesting cover used by mallards and gadwalls seems to be less attractive to blue-winged teal.
The high mobility and low breeding philopatry of blue-winged teal are important to the development and evaluation of management strategies for breeding populations. Breeding pairs may select home ranges opportunistically in response to wetland conditions encountered during spring moves. Use by blue-winged teal of areas that have undergone intensive habitat management may depend largely upon habitat quality in the surrounding regional landscape.
Development of partnerships by agencies in numerous countries is essential to ensure the long-term availability of high-quality wetland systems for use by blue-winged teal. Wetland loss and degradation in neotropical wintering areas have been as great or greater than in northern prairie breeding habitats. Effective wetland management, protection, and restoration are important throughout the range of the blue-winged teal.
Suggested Reading
Bellrose, F. C., editor. 1980. Ducks, geese, and swans of North America. 3rd ed. Stackpole Books, Harrisburg, Penn. 540 pp. Bennett, L. J. 1938. The blue-winged teal: its ecology and management. Collegiate Press, Inc., Ames, Iowa. 144 pp.
Botero, J. E., and D. H. Rusch. 1994. Foods of blue-winged teal in two neotropical wetlands. Journal of Wildlife Management 58:561-565.
Dubowy, P. J. 1985. Feeding ecology and behavior of postbreeding male blue-winged teal and northern shovelers. Canadian Journal of Zoology 63:1292-1297.
Kaiser, P. H., S. S. Berlinger, and L. H. Fredrickson. 1979. Response of blue-winged teal to range management on waterfowl production areas in southeastern South Dakota. Journal of Wildlife Management 32:295-298.
Swanson, G. A., M. I. Meyer, and J. R. Serie. 1974. Feeding ecology of breeding blue-winged teals. Journal of Wildlife Management 38:396-407.
Swanson, G. A., and M. I. Meyer. 1977. Impact of fluctuating water levels on feeding ecology of breeding blue-winged teal. Journal of Wildlife Management 41:426-433.
Taylor, T. S. 1978. Spring foods of migrating blue-winged teals on seasonally flooded impoundments. Journal of Wildlife Management 42:900-903.
Weller, M. W. 1979. Density and habitat relationships of blue-winged teal nesting in northwestern Iowa. Journal of Wildlife Management 43:367-374.
6 Waterfowl Management Handbook 13.1.8. •• 1995 Appendix. Common and Scientific Names of Plants and Animals Named in Text.
Plants Muskgrass . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Chara spp. Duckweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lemna spp. Coontail . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Ceratophyllum spp. Pondweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potamogeton spp. Bulrush . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Scirpus spp. Sedge .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Carex spp. Spikerush .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Eleocharis spp. Waterlily .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Nymphaea spp. Alfalfa .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Medicago sativa Bluegrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Poa pratensis Millet .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Echinochloa crusgalli Milo . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Sorghum vulgare Rice . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Oryza sativa Widgeongrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Ruppia maritima
Birds Blue-wingedteal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anas discors Cinnamon teal .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas cyanoptera Mallard . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anas platyrhynchos Gadwall . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Anas strepera
Invertebrates Snails .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Gastropoda Midges .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .Chironomidae Isopods . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Isopoda Beetles .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... ..Coleoptera Mosquitos .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Culicidae Fairy shrimp . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Anostraca Water fleas .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... Cladocera Dragonflies . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Odonata Water boatmen .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Corixidae
UNITED STATES DEPARTMENT OF THE INTERIOR
NATIONAL BIOLOGICAL SERVICE WATERFOWL MANAGEMENT HANDBOOK 13 Washington, D.C.  • 1995
Waterfowl Management Handbook 13.1.8. •• 1995 7
WATERFOWL MANAGEMENT HANDBOOK
13.1.11. Life History Traits and Habitat Needs of the Redhead
Christine Mitchell Custer
U.S. Fish and Wildlife Service Northern Prairie Wildlife Research Center
P.O. Box 2226 La Crosse, Wisconsin 54602
Redheads are one of five common diving duck species in North America. They are in the same taxonomic group as the pochards or bay ducks and are most similar in appearance and behavior to the canvasback. Smaller body size, late breeding, wintering in southern areas, and tolerance to salt in winter and in breeding areas differentiate the redhead from the canvasback and suggest an evolutionary origin in the arid areas of the West. Parasitism of other waterfowl nests is more pronounced in redheads than in other North American waterfowl. These and other aspects of the biology of the redhead are the subject of this leaflet. Readers who are interested in general references on redheads are referred to Palmer (1976) or Bellrose (1980).
Distribution
Redheads breed in unforested areas with semipermanently to permanently flooded palustrine wetlands that support persistent emergent vegetation. The highest numbers of redheads breed in the prairies and parklands of Manitoba, Saskatchewan, North Dakota, and South Dakota
Species Profile—Redhead
Scientific name: Aythya americana (Eyton) Weight in pounds (grams):
Adults—male 2.4 (1,087), female 2.1 (953)
Immatures—male 2.1 (953), female 1.9 (862)
Age at first breeding: 1 or 2 years
Clutch size: 7−10 eggs
Incubation period: 24−25 days
Age of fledging: 10−12 weeks
Nest sites: Semipermanently and seasonally flooded palustrine wetlands with persistent emergent vegetation.
Food habits: Omnivorous, except in winter; shoalgrass rhizomes and wildcelery winter buds during winter; tubers, rhizomes, and parts of aquatic vegetation, and aquatic invertebrates (insects, crustaceans, and mollusks) during spring, summer, and fall.
(nest densities = 10−25/mile2 [4−10/km2]). Nest densities are highest in the marshes of Nevada and Utah (180−550/mile2 [69−214/km2]; Fig. 1) where this species may have first evolved.
Redheads winter on brackish to hypersaline waters in the southern United States and in Mexico. An estimated 80% of redheads winter on the hypersaline Laguna Madre along the Gulf Coast of northern Mexico and southern Texas, but some select other parts of the Gulf Coast and the southern Atlantic Coast (Fig. 1). Migration routes to
Fish and Wildlife Leaflet 13.1.11. •• 1993 1 Fig. 1. Distribution of important breeding and wintering areas of redheads.
these wintering areas do not follow flyways. Redheads that breed in the Pacific Flyway and in the Central Flyway winter in the Central Flyway. Few redheads migrate through the Mississippi Flyway.
Spring Migration
Most redheads depart wintering areas in the Laguna Madre within 2 weeks in early March and wintering areas on the Atlantic Coast in mid-March (Fig. 2). They move through Iowa, Kansas, and Nebraska in March and reach Canada by mid-April. They are considered midseason migrants because they migrate later than mallards, green-winged teals, and northern pintails but earlier than gadwalls and ruddy ducks.
Breeding
Wetland Habitats
In the prairie potholes of Montana and northwestern Iowa and in the intermountain West, redheads use two types of permanently and semipermanently flooded palustrine wetlands for breeding. When they first arrive (prelaying period), redheads feed in large, deep, open areas (>1 acre
[0.4 ha]) with submersed aquatic vegetation (Fig. 2). They use smaller, more shallow permanent to semipermanent wetlands with blocks of dense emergent vegetation for nesting (laying and incubating eggs). Wetlands that redheads use during prelaying and brood rearing are similar. Essential elements include a good supply of preferred foods such as invertebrates and submergent plants, ample water depth for escape
2 Fish and Wildlife Leaflet 13.1.11. •• 1993 (>4 ft [>1.2 m]), and large open areas where approaching predators are visible.
Redheads use widgeongrass in saline lakes or energy-rich seeds in shallow, temporary ponds during the prelaying and laying periods in North Dakota. They rely on deep, open areas during droughts when shallow-water areas are not available. Because of low rates of nutrient recycling and a scarcity of feeding areas in open water, the quantity of food may not be as great as in shallow-water areas. Broods in all areas use shallow (<2 ft [ <0.6 m]) ponds if emergent vegetation is available for escape cover.
Impoundments and other intensively managed wetland complexes in California and Wisconsin are used by redheads. In Wisconsin, redheads nest in semipermanently flooded cattail marshes or hardstem-bulrush marshes but feed in nearby seasonally flooded impoundments managed for moist-soil plants (rice cutgrass and smartweed). Initially, broods use areas with abundant insect larvae (such as seasonally flooded impoundments) and later move to more open areas (such as
Fig. 2. The chronology of important life history events in the annual cycle of the redhead.
semipermanent impoundments) with pondweeds and duckweed.
Nest Site Requirements
Wetlands that are 5 acres (2.0 ha) or larger and not farther than 0.25 miles (0.4 km) from large permanent or semipermanent lakes provide optimum nesting habitat. Females usually place nests in dense bulrush or cattail stands that are interspersed with small (2−3 yd2 [1.7−2.5 m2]) areas of open water. Wetlands that are smaller than 1 acre (<0.4 ha) must contain large blocks of emergent vegetation for adequate seclusion and protection of nesting redheads.
Redheads begin building nests over water with remnants of the previous year’s vegetation and use new vegetation as it becomes available. Redheads seem to prefer to nest in hardstem, slender, and Olney bulrushes but also use river and awned sedges, narrow-leaved and common cattails, and whitetop. These plants offer a firm structural framework for the nest and cover for above the nest. A residual stem density of 35−45 bulrush
Fish and Wildlife Leaflet 13.1.11. •• 1993 3 stems/ft2 (350−450 stems/m2) or 3−5 cattail stems/ft2 (32−52 stems/m2) provides adequate cover and a foundation for the nest.
The presence of water seems more important than specific vegetation for nesting. Although redheads do not always nest over water, their nests are usually placed within 10−13 ft (3−4 m) of open water. However, redhead nests have been reported as far away as 755 ft (230 m) from open water. Stable water levels are important to nesting success. The bottom of the nest is usually between 2 and 10 inches (4−24 cm) above the water. If water levels rise, nests may be lost to flooding if females cannot raise the level of the nests. If the wetland dries, nests may be destroyed by predators or deserted.
Brood Size and Chronology
The brood size of redheads averaged 7 in Iowa and 5 in Nevada; most losses of young occurred within the first few days of life. The female usually deserts her brood when the ducklings are about 8 weeks old and still flightless. In contrast, ring-necked ducks and many dabbling duck species do not desert their yet-flightless young. Young redheads fly at 10−12 weeks.
Food Habits
During spring migration and the breeding season, adult redheads are opportunistic and omnivorous. In spring in North Dakota and Canada, redheads feed primarily on protein-rich invertebrates, including Diptera larvae and Trichoptera (>50% by volume). Much of their remaining diet consists of bulrush seeds and sago pondweed buds (≤15% by volume). In North Dakota and Wisconsin, breeding redheads may rely on seeds of moist-soil plants (smartweed, rice cutgrass, bulrush) when invertebrates are scarce. In Nevada, adult redheads consume bass eggs, odonate nymphs, and seeds and vegetative parts of sago pondweed, alkali bulrush, and muskgrass.
Studies in North Dakota did not reveal diet shifts, but some studies in Wisconsin revealed different proportions of invertebrates, seeds, and vegetation in the diet among prelaying, laying, and postlaying females. Redheads may have a physiological need for a seasonal shift in diet, but such a shift may not always occur because the desirable foods are not available.
Redhead ducklings eat a wide variety of foods, including insect larvae, seeds, muskgrass oogonia, and tubers. The ducklings usually move from a diet that is high in animal matter just after they hatch to a diet of almost exclusively plant matter as they approach fledging. In Wisconsin, ducklings eat mainly Hemiptera nymphs and adults, Diptera larvae, and bulrush seeds during the first 3 weeks of life. As they grow older, ducklings switch to a diet of mainly vegetation such as sago and slender pondweed, duckweed, and bulrush achenes.
Reproductive Strategy
Redheads may lay as much as 75% of their eggs in the nests of other waterfowl; as much as 50% of a redhead’s production is from parasitic eggs. Redheads seem to follow a dual strategy. In favorable years (abundant food, normal water levels and weather conditions), redheads increase their fecundity by laying 6−10 parasitic eggs before they initiate normal nesting. Parasitic eggs are produced without the time, energy, and risk associated with nest building, incubation, and brood rearing. In poor years (less abundant food or drier water conditions), younger females usually are entirely parasitic and older females nest normally, but neither age class does both. Although the hatching rate of parasitic eggs is about half that of nonparasitic eggs (90% hatching rate), females that also nest normally increase their fecundity with parasitic eggs.
The number of parasitic eggs per host nest averages between 3 and 5 in nests of canvasbacks, 4 in nests of lesser scaups, and 3 in nests of other species. Parasitism lowers the productivity of the host species because there are fewer host eggs in parasitized nests. Some of the host’s eggs are pushed from the nest during the intrusion by the parasitic redhead. Redhead parasitism rates increase with increasing densities of other duck species. Redheads also parasitize nests of mallards, northern pintails, northern shovelers, gadwalls, American wigeons, blue-winged and cinnamon teals, ruddy ducks, and other redheads. The selection of host species may result from overlapping nest chronologies and selection of similar nesting habitat.
Postbreeding Dispersal and Fall Migration
The postbreeding dispersal of males and nonbreeding females begins in June (Fig. 2), and breeding females disperse when their young are 8
Fish and Wildlife Leaflet 13.1.11. •• 1993 4
weeks old or older. Redheads of both sexes and all ages usually move north from their breeding locations to large lakes and reservoirs before molting and the subsequent fall migration. Large lakes may provide molting, flightless redheads with protection from predators and a rich food source. One very important lake for staging and molting, especially for males, is Lake Winnipegosis in Manitoba. At peak migration in 1975, an estimated 144,000 redheads were on that lake. In Utah, flightless adults usually remain in the wetland complex where they nested.
Males are flightless during late July and early August. Females become flightless approximately 6 weeks after they desert their broods. Flightless redheads usually swim or dive to escape; unlike many dabbling ducks, they rarely flap across the water.
Postbreeding adults in Manitoba eat primarily winter buds and parts of sago pondweed and muskgrass. They also ingest lesser amounts (<5% dry weight) of bulrush achenes, widgeongrass, and midge larvae and adults.
Winter Habitats and Behavior
Eighty percent of all redheads winter on the Laguna Madre of Texas and Mexico. When redheads first arrive on the hypersaline Laguna Madre, they make daily trips to adjacent freshwater ponds. They also select feeding sites with the lowest possible salinities (approximately ≤30 ppt) in the Laguna Madre. As their salt glands increase in size, the requirement for fresh water daily diminishes. By mid-to late December, fewer redheads travel to freshwater wetlands each day. The number of redheads that seek fresh water later in winter is determined by salinities in the Laguna Madre. Where salinities are high (45−60 ppt), 50% or more of the redheads are on fresh water daily throughout winter. Where salinities are lower (30−35 ppt), fewer than 15% visit fresh water daily. Freshwater sites that redheads frequent usually have salinities of less than 15 ppt and are usually within 2−4 miles (4−7 km) of feeding areas. Redheads use freshwater sites for drinking, preening, and bathing but not for feeding.
Although redheads are diving ducks, they feed most often by head dipping or tipping up (>75% of the time) in 5−12-inch-deep (12−30-cm) water on the Gulf Coast. Redheads spend about 5 h each day feeding in this manner. Feeding by diving requires
Fish and Wildlife Leaflet 13.1.11. •• 1993
about 3 times as much time and costs more energy than feeding by head dipping or tipping up. Redheads may dabble for food during the breeding season.
Food Habits
During winter, redheads in the Laguna Madre eat shoalgrass rhizomes almost exclusively, even though other vegetation is also available. As much as 15% of the food by volume (approximately 20% by weight) can be mollusks, mainly small snails such as dovesnails, variable ceriths, and virgin nerites. Whether these mollusks are ingested selectively or only incidentally to rhizome gathering is not known. In the Chesapeake Bay, wintering redheads eat winter buds of wildcelery and sago pondweed.
Courtship and Pairing
Redheads begin pairing during winter. In southern Texas, approximately 30% of the redhead females were already paired by late December and nearly 50% by late February. Females are the more aggressive member of the pair and are usually responsible for pair defense. Paired redheads continue their courtship on the breeding areas but do not copulate until the pair bond is well established.
Population Status and Harvest
The target of the North American Waterfowl Management Plan for redheads is a population size of 760,000 birds. The average population size has been at this level for the past 2 decades (759,800 during 1970−79 and 825,800 during 1980−89). The successful maintenance of redhead populations at targeted levels may have been in part the result of closed seasons and restricted bag limits for this species. Populations also may be stable because redheads use permanent and semipermanent wetlands for breeding. Because these wetland types usually persist during droughts, redheads are more likely to have a place to nest than are other waterfowl species that rely on temporarily or intermittently flooded wetlands. Furthermore, redheads are less traditional than canvasbacks in their choice of breeding areas and are therefore more likely to move into different breeding areas to take advantage of adequate water conditions.
Redheads make up 2% of the North American ducks but less than 1% of the harvested ducks in
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the United States. The average number of harvested redheads per year was 184,000 during 1971−79 and 171,100 in 1982 and 1983 but only 37,400 during 1989−91. The reduction in number of harvested redheads between the 1970’s and 1989−91 is paralleled by a reduction in the number of hunter days and the size of the seasonal bag per hunter. Most redheads are harvested in the Central Flyway (1−3% of the total duck harvest), and fewest are taken in the Atlantic Flyway (0.1−0.6% of the total duck harvest).
Implications for Management
Because redheads need a combination of habitats during the breeding season and are specialists during the postbreeding and wintering portions of their life cycle, they offer a challenge to managers. Management for redheads in the prairies should focus on wetland complexes. Deeper water with invertebrates or shallow water with moist-soil plants should be made available during the prelaying period. Water levels should be kept constant during the laying and incubation periods to reduce losses of clutches from flooding or from predators if the area becomes too dry. Recently flooded areas with high invertebrate populations should be available during the first few weeks of the brood period and should be followed by access to deeper water with ample pondweeds.
The parasitic nature of redheads also offers a challenge to managers. An increase in the numbers of nesting redheads may be at the expense of other waterfowl species. Females whose nests are parasitized by redheads have a lower productivity than conspecifics whose nests are not parasitized.
Large concentrations of postbreeding redheads occur on only a few large lakes that provide protection from predators, a rich food supply, and minimal human disturbance. Because these traditional postbreeding areas are limited, they have to be preserved.
During winter, redheads on the Laguna Madre prefer shallow (5−12 inches [12−30 cm] deep), open water with shoalgrass on the bottom. Especially early in winter before they have acclimated to hypersaline conditions, redheads also require a source of fresh drinking water within 4−5 miles (6−8 km) of their feeding sites. Since the 1960’s, monotypic shoalgrass meadows declined by over 50% in certain parts of the Laguna Madre. Concurrently, recreational and industrial uses of these coastal areas increased. Important areas for redheads, especially areas in shallow water, need to be identified and protected from human disturbance and further loss of shoalgrass. When wildcelery disappeared from the Chesapeake Bay, redheads (unlike canvasbacks) did not switch to an alternate food such as Baltic macomas—they abandoned the area. This may indicate their lack of flexibility in food choice during winter and emphasize the need to protect remaining wintering habitat.
Suggested Reading
Bellrose, F. C., editor. 1980. Ducks, geese & swans of North America. 3rd ed. Stackpole Books, Harrisburg, Pa. 544 pp.
Howard, R. J., and H. A. Kantrud. 1983. Habitat suitability index models: redhead (wintering). U.S. Fish and Wildlife Service, FWS/OBS−82 / 10.53. 14 pp.
Lokemoen, J. T. 1966. Breeding ecology of the redhead duck in western Montana. Journal of Wildlife Management 30:668−681.
Low, J. B. 1945. Ecology and management of the redhead, Nyroca americana, in Iowa. Ecological Monographs 15:35−69.
Mitchell, C. A., T. W. Custer, and P. J. Zwank. 1994. Herbivory on shoalgrass by wintering redheads in Texas. Journal of Wildlife Management 58:131−141.
Palmer, R. S., editor. 1976. Handbook of North American birds. Vol. 3. Yale University Press, New Haven, Conn. 560 pp.
Sorenson, M. D. 1991. The functional significance of parasitic egg laying and typical nesting in redhead ducks: an analysis of individual behavior. Animal Behavior 42:771−796.
Weller, M. W. 1964. Distribution and migration of the redhead. Journal of Wildlife Management 28:64−103.
Woodin, M. C., and G. A. Swanson. 1989. Foods and dietary strategies of prairie-nesting ruddy ducks and redheads. Condor 91:280−287.
6 Fish and Wildlife Leaflet 13.1.11. •• 1993 Appendix. Common and Scientific Names of the Plants and Animals Named in the Text.
Plants Awnedorsloughsedge . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Carex atherodes Riversedge .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. C. lacustris Muskgrass . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Chara sp. Shoalgrass .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Halodule wrightii Rice cutgrass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leersia oryzoides Duckweeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lemna spp. Smartweeds . .. .. .. ..