U.S. Fish & Wildlife Service
Kirtland’s Warbler
Dendroica kirtlandii
Forest fires, once thought to harm the environment, are crucial to the survival of the
Kirtland’s warbler. Without fire, jack pine cones do not completely release their seeds
and the natural establishment of new jack pine stands is prevented.
Photo by USFWS; Joel Trick
The first Kirtland’s warbler in North
America was identified in 1851 from a
specimen collected on Dr. Jared
Kirtland’s farm near Cleveland, Ohio.
Biologists did not learn where it nested
until 1903 when they found a warbler
nest in northern lower Michigan. Today,
Kirtland’s warblers face two significant
threats: lack of crucial young jack pine
(Pinus banksiana) forest habitat and the
parasitic brown-headed cowbird
(Molothrus ater).
A pair of Kirtland’s warblers requires at
least eight acres of dense young jack
pine forest to nest, but often 30 to 40
acres is needed to raise their young.
Their exacting requirements for
nesting, as well as cowbird parasitism,
caused a drastic decline in numbers and
led the U.S. Fish and Wildlife Service to
list the Kirtland’s warbler as an
endangered species in 1967.
Endangered means a species is in
danger of extinction throughout all or a
portion of its range, while the less dire
threatened designation means a species
is likely to become endangered within
the foreseeable future.
Until 1995 Kirtland’s warblers had only
been known to nest in the northern part
of Michigan’s Lower Peninsula. Today,
they also nest in the Upper Peninsula,
and since 2007, have nested in
Wisconsin and Canada. They migrate
from their nesting grounds to the
southeastern coast of the United States
on their way to wintering grounds in the
Bahamas.
Kirtland’s warblers have bluish-gray
backs with black streaks, yellow
breasts, black side streaks and split
white eye rings. They measure about six
inches in length. Females are not as
brightly colored as males.
Primarily insect eaters, Kirtland’s
warblers forage for insects and larvae
near the ground and in lower parts of
pines and oaks. They also eat
blueberries.
Kirtland’s warblers nest only on the
ground near the lower branches and in
large stands of young jack pines that are
5 to 20 feet tall and 6 to 22 years old.
The tree’s age is crucial, although
biologists are not sure why. It is
possible that the birds need low
branches near the ground to help
conceal their nests. Before the trees are
six years old, the lower branches are not
large enough to hide the nest. After 15
years, these lower branches begin to
die.
Concealed by branches, overhanging
grass and low shrubs, the warbler’s
cup-shaped nest is made of grasses.
While being fed by their mates, females
incubate four to five eggs for about 14
days. After hatching, the chicks remain
in the nest for another nine or ten days
before fledging, or leaving the nest.
Once it was believed that forest fires
harmed the environment. However, we
now know that fires play an important
role in forest ecosystems. For example,
without fire, jack pine cones do not
completely release their seeds.
Suppressing forest fires prevented the
natural establishment of new jack pine
stands. Since Kirtland��s warblers will
only nest in stands of young jack pines,
the population dwindled dramatically
before scientists realized that there is a
role for fire in forest ecology — and in
the Kirtland’s warbler life history.
The second greatest threat to Kirtland’s
warbler survival is the brown-headed
cowbird. Cowbirds lay eggs in other
bird’s nests, leaving the unsuspecting
hosts to incubate and care for the young
cowbirds. This is called nest parasitism.
U.S. Fish & Wildlife Service
http://www.fws.gov/midwest/endangered
Revised September 2008
When a female cowbird lays its egg in a
nest, it often removes one of the host’s
eggs. The cowbird egg hatches a day
before the others, getting a head start
on growth. The young cowbird is bigger
and able to claim more food than other
nestlings, and may crowd or push the
other baby birds out of the nest.
Some species have developed ways to
combat cowbird nest parasitism. They
may abandon their nest and lay eggs
elsewhere or build another nest on top
of the cowbird egg. However, Kirtland’s
warblers have not developed such
defenses. Because of cowbird nest
parasitism and Kirtland’s warblers’
inability to protect their nest and young,
less than a third of their nests produced
young in 1971.
The U.S. Fish and Wildlife Service, in
cooperation with the Michigan
Department of Natural Resources, the
U.S. Forest Service and the Michigan
Audubon Society, initiated an
aggressive cowbird removal program in
1972 that has continued to this day. As a
result, Kirtland’s warblers now have
very good nesting success and enough
young are being produced to increase
the population.
Biologists, naturalists, and bird
watchers began to recognize the dire
plight of the Kirtland’s warbler in the
1950s. To keep track of the dwindling
numbers of Kirtland’s warblers, birders
counted the number of singing males
every 10 years starting in 1951.
Females do not sing and therefore are
almost impossible to count accurately,
but studies indicate there is
approximately one female for each male.
In 1961, the total population of males
and females was more than 1,000. By
1971 the population had plummeted to
about 400 birds. At that time, biologists
began counting singing male warblers
every year.
In 1973, the U.S. Fish and Wildlife
Service (Service) appointed the
Kirtland’s Warbler Recovery Team, the
first endangered species recovery team
established by the Service. This team
included representatives from the
Michigan Department of Natural
Resources, the Service, U.S. Geological
Survey, U.S. Forest Service and
interested citizens. The team’s job was
to determine how to save the warbler
from extinction. They identified and
prioritized conservation actions.
Today, warbler conservation measures
are working. About 190,000 acres of
public lands have been set aside by the
Michigan Department of Natural
Kirtland’s warbler populations have rebounded thanks to protection under the
Endangered Species Act and conservation measures by the U.S. Fish and Wildlife
Service, U.S. Forest Service and the Michigan Department of Natural Resources, .
Biologists counted 1,803 singing male Kirtland’s warblers in 2008.
Photo by Ron Austing
Resources, the U.S. Forest Service and
the Service specifically for Kirtland’s
warbler management. From a low of
167 in 1974, the number of singing males
increased to 1,803 in 2008.
The recovery team has recommended
that 38,000 acres of warbler nesting
habitat always be available—enough to
reach the recovery goal. Since the trees
continuously grow older and warblers
cannot nest in forests older than about
22 years, land managers must create
new habitat every year. About four
thousand acres of forest are clearcut
and 2-year-old jack pine seedlings
planted each year. The cut trees are
chopped and used for fuel or particle
board —nothing is wasted. Over
ninety-four percent of the warblers
counted in the 2008 census were on these
managed land areas.
A portion of the Michigan Department of
Natural Resources annual habitat
management is funded through State
Wildlife Grant money from the U.S. Fish
and Wildlife Service. In recent years,
the amount of these grants has
decreased, along with other funding for
similar work by the U.S. Forest Service
and the State of Michigan.
Due to many dedicated people, the
Kirtland’s warbler has met the recovery
population goal. However, as a
conservation-reliant species, the
continued success of Kirtland’s warbler
is dependant on annual habitat
management and cowbird control. It is
hoped that soon, provisions can be made
to ensure that these management
activities are continued into the future,
allowing Kirtland’s warblers to be
removed from the list of threatened and
endangered species. Once these
commitments are in place, we can be
assured that Kirtland’s warbler will
continue to search out young jack pine
forests each spring for generations to
come.
