Life History
The endangered Kirtland's warbler is one of the rarest members of the wood
warbler (Parulidae) family. It is a bird of unusual interest for many reasons.
It nests in just a few counties in Michigan's northern Lower and Upper
peninsulas, in Wisconsin and the province of Ontario and, currently, nowhere
else on Earth. Its nests generally are concealed in mixed vegetation of grasses
and shrubs below the living branches of five to 20 year old jack pine (Pinus
banksiana) forests. The male Kirtland's warblers' summer plumage is composed
of a distinctive bright yellow colored breast streaked in black and bluish gray
back feathers, a dark mask over its face with white eye rings, and bobbing tail.
The female's plumage coloration is less bright; her facial area is devoid of a
mask. Overall length of the bird is less than six inches.
Because of its restricted home range and unique habitat requirements, the
Kirtland's warbler probably has always been a rare bird. Scientists did not
describe the species until 1851 when a male was collected on the outskirts of
Cleveland, Ohio. That first specimen was sent to the Smithsonian Institution in
Washington, D.C. The species eventually was named in honor of Dr. Jared P.
Kirtland, a physician, teacher, horticulturist, and naturalist who authored the
first lists of birds, mammals, fishes, reptiles, and amphibians of Ohio.
The winter range of the Kirtland's warbler was discovered in 1879 when a
specimen was collected on Andros Island in the Bahama Islands archipelago. All
sightings or collections of wintering Kirtland's warblers since then have been
in the Bahamas and in the Turks, Caicos, and Hispaniola islands. Because of its
subtle fall and winter dull brown plumage and behavior, population information
on the warbler's winter grounds is scarce. Additional research, education, and
public outreach are required during the warbler's eight month stay in the
Bahamas. Kirtland's warblers are one of more than 200 neo-tropical migratory
species that nest in North America and winter in the tropics.
It was not until 1903 that Norman A. Wood discovered the first nest in Oscoda
County in northern lower Michigan. Until 1996, all nests were found within 60
miles of this site. Since then, a small number of nests have been found each
year in Michigan's Upper Peninsula. Nesting also has occurred in Wisconsin and
the province of Ontario.
The diet of the warbler includes many different insect species at various
developmental stages, including caterpillars, butterflies, moths, flies,
grasshoppers, as well as ripe blueberries, when in season.
Breeding
Male Kirtland's warblers arrive back in Michigan from the Bahamas between May 3
and May 20, a few days ahead of the females. The males establish and defend
territories and then court the females when they arrive. The males' song is
loud, yet low pitched, ending with an upward inflection. As the female builds a
nest of leaves and grass, lined with mosses or deer hair, the male begins to
bring her food. This duty continues through laying and the incubation process,
with which the males rarely help. Four to five cream white eggs speckled and
blotched with brown are laid in late May, followed by an incubation of 13-16
days. Both parents feed the chicks, which grow quickly and have left the nest
within nine days, staying in the undergrowth and lowest branches of the trees.
Within five weeks, the parents have ceased feeding their young.
Jack Pine Habitat
The jack pine forest community provides the primary nesting habitat for the
Kirtland's warbler. This forest species is adapted to dry land conditions and
has been present on the sandy outwash plains of northern Michigan since the
retreat of the Wisconsin ice sheet about 14,000 years ago. A narrow, band of
jack pine habitat can be found across the north central states and the province
of Ontario.
The Kirtland's warbler has very restrictive habitat requirements. In addition to
being ground nesters, Kirtland's warblers prefer jack pine stands over 80 acres
in size. Those stands, which are most suitable for breeding, are characterized
by having dense clumps of trees interspersed with numerous small, grassy
openings, sedges, ferns, and low shrubs. The birds nest on the ground under the
living branches of the small trees. Jack pine stands are used for nesting when
trees are about five feet high or about five to eight years of age. Nesting
continues in these stands until the lower branches of the trees start dying, or
when the trees reach a height of 16 to 20 feet (about 16 to 20 years of age). A
breeding pair of warblers usually requires about six to ten acres for their
nesting territory, although as little as 1.5 acres may be adequate under optimal
conditions.
Nearly all nesting occurs in jack pine stands where the soil type is Grayling
sand. This is an extremely well drained sandy soil with low humus and nutrient
content. Water percolates through the sand so quickly that nests seldom are
flooded during a rainstorm. This soil also supports the plant community required
for nesting habitat.
Fire always has been an important disturbance factor in the jack pine barrens.
The young jack pines upon which the Kirtland's warbler depends grow after fire
removes older trees and rejuvenates the forest. Heat from fire opens jack pine
cones to release seeds. Fire also prepares the ground for the germination of the
seeds.
Historically, the jack pine barrens were maintained by naturally occurring
wildfires that swept through the region. The jack pine held little value for the
lumbermen who came in search of white pine. Once logging activity ended in the
1880's, the continuing forest fires helped increase the range of jack pine,
which created more nesting habitat. As a result, the Kirtland's warbler
population reached its peak between 1885 and 1900.
With the advent of modern fire protection and suppression efforts, forest
management practices did not emphasize the regeneration of jack pine.
Consequently, there was a drastic decline of available warbler nesting habitat,
and its numbers plummeted. In order to provide appropriate habitat for the
Kirtland's warbler, the U.S. Department of Agriculture Forest Service and the
Michigan Department of Natural Resources created four areas within state and
national forests to be managed specifically for Kirtland's warbler nesting
habitat between 1957 and 1962. By 1973, these areas contained 53% of the nesting
population.
It was clear that providing more jack pine areas would be necessary to increase
the Kirtland's warbler population. During the mid 1970s, some 134,000 acres of
jack pine were designated for management as Kirtland's warbler nesting habitat
within 24 management areas of state and national forests. Additional lands were
added through the 1990's to bring the total public land specifically set aside
for the Kirtland's warbler to more than 150,000 acres.
Jack pine stands are managed by logging, burning, seeding, and replanting on a
rotational basis to provide approximately 38,000 acres of productive nesting
habitat at all times. By carrying these stands to a 50 year rotational age,
nesting habitat can be maintained for the warblers with little sacrifice to the
commercial harvest of jack pine. These jack pine stands also provide habitat for
the upland sandpiper, Eastern bluebird, white tailed deer, black bear and
snowshoe hare, and for several protected prairie plants, including the Allegheny
plum, Hill's thistle, and rough fescue. Unfortunately, the jack pine habitat
also provides a home for the brown headed cowbird, an undesirable nest parasite.
Brown-headed Cowbirds
The brown headed cowbird (Molothrus ater), once called the "buffalo bird," was
common in the open plains. Cowbirds followed the vast herds of American bison
and then cattle, eating the insects that swarmed around the hoofs of the grazing
herds. Unable to move with the wandering herds while maintaining a nest, these
birds developed an unusual behavior; they began to lay their eggs in the nests
of other birds. The cowbird chicks, which hatch earlier than most songbirds, are
more aggressive and will out-compete their nest mates for food. This added
competition reduces the number of non cowbird young that fledge.
As land in Michigan was opened up during logging and agricultural development,
cowbirds moved into the new areas, and the Kirtland's warbler was an extremely
vulnerable host. The egg laying activity of the cowbirds began to impact the
Kirtland's warbler population.
Studies have revealed that when one cowbird egg is laid in a warbler nest, only
one to three warbler chicks may survive. If two cowbird eggs are laid and
hatched in a warbler's nest, none of the warbler chicks survive. Heavy cowbird
parasitism is believed to have been a major factor in the decline of the
Kirtland's warbler population. In 1972, the U.S. Fish and Wildlife Service, in
cooperation with the USDA Forest Service, Michigan Department of Natural
Resources, and the Michigan Audubon Society, began controlling cowbirds with
large live traps that are placed in Kirtland's nesting areas during spring and
early summer. The traps, which are baited with millet, water, and several live
cowbirds, are checked daily and any trapped cowbirds are euthanized. Non target
species are released unharmed. Since 1972, an average of 4,000 cowbirds per year
have been removed from Kirtland's warbler breeding areas.
Kirtland's warbler reproductive success has improved dramatically since cowbird
trapping began. The nest parasitism rate has declined from the 1966 71 average
of 69% to less than 5%. Average clutch size has increased from 2.3 eggs per nest
to more than four. The average number of young warblers fledged per nest
increased from less than one to almost three birds during the same period. The
2002 annual census counted over 1000 singing males for the second year in a row.
Nesting population size is estimated annually by counting the singing male
Kirtland's warblers. The songs of the males are distinct, loud and melodious,
and can be heard at a distance of one quarter mile. These counts of the singing
males are doubled to determine an estimate of the nesting population. Biologists
and other agency personnel, researchers, and volunteers conduct this survey. The
first survey was conducted in 1951 and has been done annually since 1971.
Additional jack pine areas in the Great Lakes region are being surveyed. Unmated
males have been found in Wisconsin, Ontario, and Quebec.
Bahamian Connection
In the late 1990s, a partnership that includes agencies in the U.S. and the
Bahamas was formed to identify and protect habitats within the Bahamas that are
used by wintering songbirds, including the Kirtland's warbler. The partners
include The Nature Conservancy, Canon USA, the Bahamas Ministry of Agriculture
and Fisheries, and the Bahamian National Trust. Protection of the wintering
grounds includes the development of pine islands and controlling the impact on
the use of the forested and broad leaved scrub areas by wild cats.
In 1997, State and Federal government agencies in Michigan, working in
partnership, hosted a delegation from the Bahamas. The Bahamian delegates came
to Michigan to review endangered species management and to learn more about the
Kirtland's warbler, its summer nesting locations, and interagency management.
This visit began an international effort to protect this bird in its summer,
fall, and wintering habitats.
The following year, a research team of state and federal agencies joined
international representatives in the Bahamas to discuss future Kirtland's
warbler recovery projects. These projects include: (1) training birding groups
in the identification and monitoring of Kirtland's warblers and other rare
resident birds, (2) surveying the Bahamian chain of islands to identify critical
wintering bird habitats and, (3) forming partnerships to support conservation
work in the Bahamas and Michigan.
The Recovery Plan
A Kirtland's Warbler Recovery Plan was developed in 1976, and updated in 1985,
to provide state and federal agency personnel with a structured guide to direct
management efforts toward increasing the Kirtland's warbler population. The
primary recovery objective is to establish and sustain a Kirtland's warbler
population throughout its known range at a minimum level of 1,000 pairs using
adaptive management techniques. A major component of the original plan is
habitat management. In 1981, the Kirtland's Warbler Management Plan for Habitat
in Michigan was initiated. It identified strategies that are necessary to
maintain and develop nesting habitat for the Kirtland's warbler, and established
the following objectives:
- DEVELOP and maintain some 36,000 40,000 acres of suitable nesting habitat for
the Kirtland's warbler on a sustained basis. This will be done through planned
rotation cuttings on 140,000 acres of jack pine stands within designated
management areas.
- PROTECT the Kirtland's warbler on its wintering grounds and along its
migration route.
- REDUCE key factors adversely affecting reproduction and survival of the
Kirtland's warbler.
- MONITOR breeding population of the Kirtland's warbler to evaluate responses
to management practices and environmental changes.
- Develop and implement emergency measures to prevent extinction.
Education and Nature Tourism
The Kirtland's Warbler Recovery Team recognizes the need to review several
factors necessary in managing this endangered species. These include the role of
information and educational outreach in resource management, the development and
increased tourism interest in the jack pine forests, the Au Sable River
corridor, and the wintering grounds of the Kirtland's warbler. The team supports
several educational events, projects and wildlife viewing opportunities. These
include a video, guided Kirtland's warbler tours, annual Kirtland's Warbler
Festivals, and the self guided auto tour through the jack pine ecosystem.
Educational outreach is expected to continue in Michigan, and several new
programs are being developed in the Caribbean. A source of continued funding
will be necessary to maintain the current level of resource management and
research, and is vital to expanding educational outreach efforts here as well as
in the Bahamas.
We invite you to become a partner in helping the Kirtland's warbler by
supporting the many efforts of the Kirtland's Warbler Recovery Team.
How You Can Help
- Staying out of posted nesting areas.
- Camping only in designated campgrounds.
- Staying with the tour guides and following their instructions.
- Operating all vehicles only on open roads and designated trails within the
area.
- Leaving your pets in a safe area. Pets are not allowed to run in posted
nesting areas.
- Not using recordings or imitations of Kirtland's warbler songs to attract
birds.
- Learning more about endangered species and ways you can help them and their
habitats.
- Sharing this information with your family and friends.
- Being extremely careful with fire.
- Donating to the Nongame Fish and Wildlife Fund.
Quick Facts
- The Kirtland's warbler was first described in Ohio in 1851
- It is commonly referred to as the jack pine warbler
- This songbird is one of 56 species of wood warblers found in North America
- Its nesting habitat is jack pine stands from 5 20 years old
- It nests on the ground under living jack pine branches
- Management of jack pine forests includes clear-cutting, fire, replanting, and
reseeding
- Adult Kirtland's warblers are lightweight birds, weighing 1/2 oz
- Its average life expectancy is two years
- The diet of the warbler includes many different insect species, as well as ripe
blueberries.
- Breeding males have plumage of blue gray with black streaks
- Migrating at night, this wood warbler can come in contact with towers and other
high structures
- It spends the fall and winter seasons in the Bahamas
- Cowbird management is necessary for the Kirtland's warbler's survival
- Brown headed cowbirds are parasites of Kirtland's warbler nests
Kirtland's Warbler Singing Male Census Results
1951-2002
Click on image for a larger version.
Non-DNR Links
Dendroica kirtlandii (University of Michigan, Museum of Zoology)
Species Profile (U.S. Fish & Wildlife Service)
Identification Tips & More (USGS Patuxent Wildlife Research Center)
Wildlife Species:
Dendroica kirtlandii (USFS Fire Effects Information System)
Kirtland's Warbler Page (U.S. Forest Service)
Wild File: Kirtland's Warbler (Georgia Wildlife Federation)
Kirtland's Warbler Festival (Kirtland Community College)
Kirtland's Warbler Auto Tours (US Forest Service)
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