A Bird of Fire
Kirtland's warbler, Dendroica Kirtland, is a very rare member of the subfamily of wood warblers (Parulinae). Its plumage is a beautiful blue-gray above and bright yellow below. The warbler's fame can be owed greatly to its rarity. It has been said, Ounce for ounce, the Kirtland's warbler has drawn more official interest and created more controversy than any other songbird in history.
The Kirtland warbler's nesting grounds can be found in central lower Michigan. These areas are closed to public entry between May 1 and August 15, except by free-guided tours. There are two tours, one run by the Michigan Dept. of Natural Resources in Mio; the other conducted by the U.S. Fish and Wildlife Service in Grayling. Each tour provides great views of singing males; perched on dead snags, or singing from the tallest point of the jack pine trees.
Kirtland's warbler was discovered on May 13, 1851. by Charles Pease near Cleveland, Ohio. The species was named in honor of his father-in-law, Dr. Jared P. Kirtland, pioneering author and naturalist in Ohio. The Bahamas Islands' winter range was found when a specimen was collected on Jan. 9, 1879, on Andros Island. In July 1903, the nesting grounds were discovered in lower Michigan.
The U.S. Forest Service and Michigan Dept. of Natural Resources, between 1957 and 1962, set aside 4 areas in State and National Forests to be managed to benefit Kirtland's warbler by providing nesting habitat for the declining species. In 1971, the U.S. Fish and Wildlife Service began a cowbird control program. In early 1975, following guidelines set by the Endangered Species Act of 1973; a Kirtland's Warbler Recovery Team was named by the Secretary of the Interior to coordinate the efforts of the Michigan DNR, Fish and Wildlife Service, U.S. Forest Service, the Michigan, Detroit, and Pontiacs Audubon Societies, and the Michigan Natural Areas Council. One of the goals of the recovery plan was to reach and maintain at least 1,000 breeding pairs of warblers.
Kirtland's warbler has very restrictive habitat requirements. Soil in the area is poor and low in nutrients (Grayling Sand). It is also very dry and porous, producing a plant community necessary for nesting habitat. The most common plants here include blueberry and various grasses. There are usually dense clumps of pines interspersed with small grassy openings. The warbler nests in the grassy archways beneath the lower limbs of young jack pines.
The warbler nests in an area that stands usually over 80 acres in size. Ideally, the trees are 5-15 years old and 5-15 feet high. When older trees' lower branches die off, they no longer provide cover, and the birds move on.
Plantations of 100 acres have been successful in attracting warblers. Here, jack pines are planted in rows, alternating with grassy clearings. When they reach 50 years of age, mature pines are harvested for timber, and the residual brush and plants are burned.
The Role of Fire
Because of fire the jack pine and the Kirtland's warbler exist today. Heat from fire opens jack pine cones to release the seeds. Fire also helps prepare the ground for seed germination by making available to the soil nutrients stored in forest litter and living trees. Competing trees die and wind scatters the seeds. Fire dries millions of cones at once. Then they open and drop many seeds on the ground beneath the burned trees. The forest canopy is burned away, and sunlight stimulates the growth of ground cover and new jack pines. Areas are burned on a rotational basis, supplying nesting habitat at all times.
Male Kirtland's warblers arrive on the breeding grounds from May 11-14 and immediately establish territories. The females arrive less than a week later. A pair requires about 30 acres for their territory, but can use as little as 10. At this tie, the male sings his loud and lively song, while the female builds the nest among ground plants, often at the edge of an opening in the pines, usually not far from the base of a tree. Pair formation occurs from May 20-30; nest building and egg-laying is completed by June 10.
If undisturbed by cowbirds, females will normally lay 5 eggs in the first clutch. Kirtland's sometimes attempt a second clutch, averaging 4 eggs, after a successful first nesting, or, if a nest has been lost to a predator. Incubation requires 13-16 days; eggs hatch between June 12 and 26. Both adults feed the young, but the female does all the brooding. The young develop quickly, doubling their weight every 2 days, until they are 5 days old. They are out of the nest by the 9th day. Each parent takes part of the brood and cares for it exclusively. The young spend the first 2 weeks out of the nest in the undergrowth and lower branches of the jack pines, being fed a diet of insects and blueberries. By the 3rd week they begin to gather most of their own food, and by the 5th week parental feeding has ceased.
The parasitic, brown-headed cowbird has no nest of its own, but lays its eggs in the nests of the Kirtland's warbler. The cowbirds usually lay 1 or 2 eggs about the same time as the warbler does. The intruder's hatch 2 or 3 days sooner than the warblers, giving the young cowbirds a head start on warbler nest-mates. Also, female cowbirds often remove warbler eggs from nests. The cowbird nestling is larger and more aggressive than the warblers, getting more food. With one cowbird in the nest, 1-3 warbler chicks may survive. If 2 cowbirds hatch, the warblers don't have a chance.
Fearing possible extinction of the species, the U.S. Fish and Wildlife Service and U/S. Forest Service, in cooperation with Michigan DNR and the Michigan Audubon Society launched a cowbird control project in 1972. Trapping is conducted from late April to early July. By 1983, 40,000 cowbirds were removed. Parasitism decreased from 74.6% (1957-'71) to 6.1% (1972-'77). During these periods, the average warbler eggs per nest rose from 3.3 to 4.6. Fledglings per nest rose from 0.81 to 2.67. (Data from "Kirtland's Warbler" by Walkinshaw. (Predation is now realized as a formidable threat. Known nest predators, the blue jay, 13-lined ground squirrel, and red squirrel are considered the 3 worst enemies of Kirtland's warbler since the elimination of the cowbird.)
In late August, some of the warblers begin their journey to the Bahamas; by mid-September, all have left. Little is known of the Kirtland's warbler's existence outside Michigan. It is seldom seen in migration, and only a few birds have been observed in the deciduous scrub and pine forest in the Bahamas winter home.
Kirtland's warbler is the first songbird to have its entire population censuses, due to the Kirtland's restricted range. The census is taken by counting singing males. Since the warbler is basically monogamous, the total breeding population is approximately double the singing male count. These counts began in 1951 (432 singing males); 1961 (502), 1971 (201) and yearly since then. The dramatic decline seen in 1971 was due to cowbird parasitism. This year luckily, during the 2003 official census, 1,202 singing males were counted. Comparing this to last years count of 1,050 the Kirtland warbler population is on the rise.
Kirtland's Warbler Today
The total Kirtland's management area is 135,000 areas (78,000 state, 55,000 federal lands), mostly in 6 counties in Michigan. This summer, the warblers occupied about 7,000 acres. Today, researchers study both the summer and winter homes of the warbler. Scientists are considering the possibility of expanding Kirtland's habitat outside of Michigan to Canada and other northern states. Recently, 14 singing males were found in the upper peninsula counties of Michigan. singing males were counted in Canada during the census period.
The survival of Kirtland's warbler is still in doubt and will require a continuing effort to provide the habitat and protection it needs.