|Listed||March 11, 1967|
|Habitat||Breeds in jack-pine forest.|
|Food||Insects and other invertebrates.|
|Reproduction||Lays eggs in a cup-shaped nest on the ground.|
|Threats||Habitat loss on both the breeding and wintering grounds.|
|Range||Michigan, Wisconsin; Canada, West Indies|
The Kirtland's warbler is a small, perching songbird, with a body length of about 6 in (15 cm). It is colored blue-gray above and yellow below, with coarse spotting on the breast and sides. Males have a black spot on the cheek, which in females is gray. There is a white-eye ring, which is broken by a dark eye line.
The Kirtland's warbler builds its nest on the ground beneath pine trees. The nest is constructed of strips of bark, grass, and other fibers, and is lined with finer grasses, pine needles, and hair. The clutch size is three to five eggs, which are white and speckled with brown. It is the only blue-gray warbler that wags its tail as it walks on the ground. The Kirtland's warbler migrates along a rather direct route between its nesting grounds in Michigan and its wintering range in the Bahamas and Dominican Republic, entering and leaving the United States along the North and South Carolina coasts.
The breeding habitat of Kirtland's warbler consists of homogeneous thickets of five-and six-year-old jack pines (Pinus banksiana ) interspersed with grassy clearings. This habitat is created and maintained by intense, periodic brushfires. The warbler requires enough ground cover to conceal its nest but shies away from areas that are overgrown. When deciduous trees begin to dominate an area, the warbler moves out. A tract of jack pine must be at least 80 acres (32 hectares) or larger to attract Kirtland's warbler. The breeding habitat is also limited to a specific soil known as Grayling sand, an infertile type that is extremely porous and well-drained. This soil type occurs in 29 counties of the lower Michigan peninsula, corresponding closely with natural stands of jack pine. On its wintering grounds in the Bahamas, the Kirtland's warbler occupies low, broad-leafed scrub, which is the prevailing habitat there.
The narrow habitat requirements of the Kirtland's warbler have always restricted its range. The breeding range is almost entirely on the lower Michigan peninsula, in Crawford, Oscoda, and Ogemaw counties, particularly in the watershed of the Au Sable River. These counties have thousands of acres of natural jack pine forest. The rare warbler may also have bred in Minnesota, Wisconsin, and Ontario. Recent studies have identified stray male warblers in jack pine tracts in these other places, but there is no evidence of nesting.
The greatest threat to the Kirtland's warbler has been habitat loss caused by the control of forest fires, and to a lesser degree forestry, agricultural, and residential developments. Forest fire control has greatly reduced the size and frequency of burns in the Au Sable River watershed to the disadvantage of the warbler. Also, forest management has encouraged the replacement of jack pines with red pine (Pinus resinosa ) or hardwoods, further reducing habitat. In the mid-1990s, only about 4,500 acres (1,800 hectares) were suitable for breeding by this species. This was a substantial reduction from the 15,000 acres (6,100 hectares) available in the 1950s and 1960s.
In 1951, a census of the Kirtland's warbler found 432 singing males, which suggested a total population of about 1,000 birds. A 1961 survey found 502 singing males, but in 1987 there were only 167. In 1993, however, the population had increased to 485 singing males, and there were 633 in 1994.
Conservation and Recovery
In 1957, the Michigan Department of Natural Resources set aside three tracts of about 25.4 acres (10.3 hectares) each to be managed for the benefit of the Kirtland's warbler. In two of these, jack pine was planted in a special arrangement to leave numerous clearings. These tracts have succeeded in attracting nesting warblers. At about the same time, the U.S. Forest Service set aside a management area of more than 4,000 acres (1,600 hectares) in the Huron National Forest in Oscoda County for the warbler. Cooperative habitat management efforts by the U.S.Fish and Wildlife Service (FWS), Forest Service, and Michigan Department of Natural Resources are providing nesting habitat for the Kirtland's warbler. Intensive land-management practices include clear-cutting jack pine stands at 50 years of age in blocks of at least 300 acres (120 hectares), prescribed burning, and replanting with jack pine.
In addition, biologists are working to remove brown-headed cowbirds (Molothrus ater ) from the breeding habitat of the Kirtland's warbler. The cowbird is a nest-parasite that lays its eggs in the nests of other birds, which incubate and raise the cowbird chick, while their own reproduction usually fails. In the 1970s, cowbirds reduced the breeding success of the Kirtland's warbler by at least 40%, and in some years almost wiped out their reproductive effort. During the 1970s, FWS personnel trapped and removed about 40,000 cow-birds, significantly decreasing the impact of parasitism. More than 3,100 cowbirds were removed from warbler breeding areas in 1994 alone. Kirtland's warbler has not recovered as quickly as hoped, however, suggesting that additional factors are constraints. Nevertheless, the survival of the rare warbler depends on continued cowbird control, as well as on intensive habitat management.
Recovery partners have also launched creative and far-reaching public information programs. Until 1994, outreach efforts consisted of free public tours daily during May and June by the FWS and Forest Service. The tours include a brief presentation about the warblers, followed by an field trip to sites where singing Kirtland's warblers could be seen. These tours have become quite popular with birders, who come from around the world to see the rare birds. In 1994, the FWS began expanding the outreach effort. One of the most significant additions to the program is a 48-mi (77-km) self-guided "watchable wildlife" auto tour with 11 interpretive sites. The tour, which has received national attention, is designed to educate the public about forest habitats and ecosystem management, in addition to Kirtland's warblers. Another public outreach effort is a festival honoring the warbler. Since 1993, the Annual Kirtland's Warbler Festival, organized by the Kirtland Community College, has been attracting birdwatchers and members of the community to learn about the bird and its habitat. These kinds of outreach events raise the awareness of the species with the public and make it easier for recovery teams to work with local landowners, users and tourists.
Mayfield, H. F. 1963. "Establishment of Preserves for the Kirtland's Warbler in the State and National Forests of Michigan." Wilson Bulletin 75:216-220.
Orr, C. D. 1975. "1974 Breeding Success of the Kirtland's Warbler." Jack-Pine Warbler 53:59-66.
Radabaugh, B. E. 1974. "Kirtland's Warbler and Its Bahama Wintering Grounds." Wilson Bulletin 96:374-383.
Shake, W. F., and J. P. Mattsson. 1975. "Three Years of Cowbird Control: An Effort to Save the Kirtland's Warbler." Jack-Pine Warbler 53:48-53.
U.S. Fish and Wildlife Service. 1976. "Kirtland's Warbler Recovery Plan." U.S. Fish and Wildlife Service, Twin Cities.
U.S. Fish and Wildlife Service. 1991. Kirtland's Warbler. Dendroica kirtlandii. Endangered and Threatened Species of the Southeastern United States (The Red Book) FWS Region 4. http://endangered.fws.gov/i/b/sab0d.html