International
Migratory Bird
Day (IMBD),
held annually
on the second
Saturday in
May, is an
invitation to
celebrate and
support
migratory bird
conservation.
IMBD Information
web http://birds.fws.gov/imbd.html
phone 703/358-2318
IMBD Sales
web http://www.BirdDay.org
phone 1-866/334-3330
January 2002
The Four Essential Elements
of Habitat
Food, Water, Cover, Space
Critical for Survival
All species of plants and animals—
including people—need a proper
combination of food, water, cover, and
space to survive and reproduce.
Together, these elements make up a
“habitat.” Without habitat, a species
cannot survive.
Since bird species are wonderfully
diverse in their forms and lifestyles, their
habitats vary tremendously. However,
regardless of location, be it sandy
seashore, tropical forest, arid grassland,
or urban neighborhood, a habitat must
fulfill the four essential needs.
• Food. Some species of birds are
herbivores, eating seeds, fruits, buds, or
flowers. Some are carnivores, eating
insects, snails, fish, other birds, or
carrion. Many species are omnivores,
eating both plant and animal matter. A
bird’s bill shape and size offer excellent
clues to the bird’s diet.
The type of food that a bird selects
depends on availability, and during
periods of abundance (for example,
during a spring fish spawning or fall
fruiting) its diet may become very
repetitive. A bird’s diet also depends on
its nutritional requirements,
which change with
season and age.
Breeding adults and
developing chicks
need additional
protein, for example.
Birds that eat plant
matter much of the
year, such as the
American Tree
Sparrow, will turn
to insects to fulfill
that need. Birds
undertaking
strenuous
migrations will
increase and alter their diets prior to
their journeys in order to accumulate
large amounts of energy in the form of
fat. As an extreme example, the
Blackpoll Warbler doubles its body
weight prior to migration!
• Water. Birds, like all living things,
require water. Most birds obtain water
by drinking—dipping with their bills and
tipping their heads back to swallow.
Pelicans have been seen standing with
their mouths open in the rain. Sea-going
birds, such as albatross, can drink
saltwater because of specialized nasal
glands that extract excess salt from the
blood. However, species with very moist
diets,such as hummingbirds and other
nectar-feeders, obtain water almost
completely from their food, and in very
arid regions, some species also rely on
metabolic water, produced as their bodies
burn fat.
Water can also be essential as a medium
for feeding and other activities. Herons
wade, puffins dive, ducks dabble, and
gulls skim the water in search of aquatic
foods. Many birds stay on the water to
rest, court, and preen. In fact, pelagic
(oceanic) species spend most of their time
out at sea, returning to land only to nest.
• Cover. Birds, nestlings in particular,
need shelter from predators and the
elements. Cover, including trees,
grasses, and rocks, also harbors foods for
birds and provides space or materials for
nesting. The requirements for cover can
be quite specific. Species often show a
marked preference for nesting and
foraging at certain heights and in certain
structures of vegetation. Cavity nesters,
such as woodpeckers, require trees of
the age and size to support suitable holes.
A bird’s needs may also change over
time. Open meadows and grasslands
provide good cover for wild turkey
chicks; as adults, turkeys can better
avoid predators in areas with mature
trees and little underbrush. Some birds
prefer no cover. Nesting terns require
sandy stretches of beach nearly devoid of
vegetation and use their bodies to shelter
their eggs and chicks.
• Space. Birds simply need the room to
find food, water, and cover. The amount
of space needed depends largely on the
availability of these elements. For
example, hawks and other raptors
require more acreage for hunting when
the abundance of prey decreases. The
need for space also mirrors the social
habits of the species. In winter, Dark-eyed
Juncos flock together, but on their
breeding grounds, these birds disperse
and defend territories.
Most species of birds space themselves
out for breeding, with males or breeding
pairs defending their territory. In
contrast, one-eighth of all bird species
nest in colonies, including swallows,
herons, gulls, and cormorants, and a
large number of young may be produced
in a small area. However, although a
nesting colony occupies less space than if
nests were widely dispersed, the birds
often require large areas nearby in which
to find food.
Multiple Habitats for Migratory Birds
Birds that migrate spend part of their
time in one habitat, and move to another
to breed. In addition to wintering and
breeding habitat, these birds require
stopover areas along their migration
routes. These habitats may be strikingly
different, depending on the seasonal
needs of the birds. The White-rumped
Sandpiper, for example, spends the
winter on beaches in Argentina,
hopscotches from wetland to wetland
across the Americas, and nests on the
mossy or grassy tundra of the high
Arctic. Because migratory species use
multiple areas, these species and their
habitats deserve our particular attention.
Conserving Quantity and Quality
Unfortunately, human activities and
development often result in the loss of
bird habitat. An area covered with
buildings or pavement simply cannot
provide the food, water, cover, and space
that birds need. To preserve healthy bird
populations, we must strike a balance
between our own habitat needs and those
of other species. With some birds, people
can establish conditions that allow for
cohabitation, such as green spaces in
their neighborhoods and cities. In other
cases, the long-term survival of a species
requires that people set aside areas from
development and disturbance.
People concerned about birds must also
protect habitat quality. Good bird habitat
must not only provide food, water, cover
and space, but must be free from
significant hazards. Birds face numerous
threats from human activity, including
poisoning by pesticides and pollutants,
entanglement in fishing nets and lines,
collisions with structures and vehicles,
and attacks by introduced predators such
as cats. People must work to reduce or
eliminate these hazards in order to allow
habitat to serve its function of providing
for a species’ survival.
Birds Need
Food
Water
Cover
& Space
