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Kirtland’s Warbler
Kirtland's
Warbler Tours Available from US Forest Service Links to Kirtland Information:
The Kirtland’s Warbler, a federally listed endangered species, is one of the world’s rarest birds. Weighing in at roughly one-half ounce, their total aggregate weight is just over 40 pounds! Its only consistent breeding grounds is the dense jack pine (Pinus banksiana) forests in Michigan's Lower Peninsula in an area 100 miles long and 60 miles wide within the Au Sable River drainage area. These birds were known as the "bird of fire" because intense heat is needed to open the jack pine cone and release the seeds. The Kirtland’s numbers plummeted when there were fewer fires causing their desired nesting areas to decline accordingly. Males arrive on last year’s breeding ground and immediately start singing to fend off rival males and to attract a mate. His loud, distinctive song can be heard up to one-half mile away as he sings from the top of a small jack pine into early June. The normal song is described as chip-chip-ce-way-o and chip chip chip-chip-chip tew tew weet weet. Females and young males arrive soon after. The females to do not sing. Seventy percent of the birds that migrate return to their breeding ground, but only 36% of the juveniles survive migration. The key to increasing their numbers is to have the right habitat for an adequate nesting site. Kirtland's Warblers are sparrow-sized, 5 ½", blue-gray to gray brown above, with a streaked back and yellow below. This bird was first described in 1851 by noted Ohio naturalist Dr. Jared P. Kirtland when it was collected near Cleveland. The nesting range was not discovered until about 1900 when some trout fishermen heard an unfamiliar bird singing in the jack pine barrens along the Au Sable River. Norman A. Wood, then University of Michigan curator of birds, is credited for finding and identifying the first nest in Michigan and for identifying its specialized habitat needs. They eat mainly insects they catch in flight as well as pine needles, grasses, and blueberries. They only nest in young jack pine forests that have a lot of small grassy openings. Each male’s territory ranges from 3.4 to 8.4 hectares and are often clustered in loose colonies. They make the nest near the base of 5 to 20 foot tall jack pines 5 to 20 years of age with live branches extending to the ground. They like sedges, grasses, berry brambles and sweet ferns as a ground cover. They also require a very specific type of soil, the Grayling Sands, which drains quickly. Without drainage, their nests which are very close to the ground would flood. Consequently, 90% of the nests are built in the drainage area of a single stream. The cup shaped nest is comprised of grasses, leaves, moss, and hair, nestled into a pit in the sandy soil. They build the nest in late May. Three to six eggs are laid between late May and mid-June and incubated for 14 days. It is the female’s responsibility to defend and care for the nest. The male brings her food. Both parents feed the young. They gain weight quickly the first five days of their life, doubling their weight every two days. The last three days they are in the nest, their growth slows down. Their energy is used to provide them with body warmth, plumage development and more chemical activity. They leave the nest when they are nine to ten days old. After they fledge, each parent is responsible for taking care of one-half of the brood. They all winter in the Bahamas in areas that contain low scrub but they roost in high shrubs overnight. The annual Kirtland’s Warbler census is taken between June 6 and June 15. Volunteers count the number of singing males and multiply by two. A census was taken in 1951, 1961, 1971, and annually since 1971. The current numbers are pretty stable from spring to spring. Researchers believe the birds are facing other problems either during migration or during the winter in the Bahamas. Also limiting the population growth can be habitat maturation and fragmentation, incomplete pairing success, fledgling mortality, yearlings locating to unsuitable habitat or places outside the breeding range. It is believed a decline of suitable habitat has decreased their numbers since habitat has been decreasing in the last 35 years (Michigan Breeding Bird Atlas, Pg. 414). Between 1961 and 1971 the population had dropped by 60%. By 1987, the total population had dropped to 167 singing males. One reason for the decline was the loss of habitat caused by improvements in wildfire prevention. Without fires, the jack pine cones do not open. Without opening and disbursing the seeds, new tress do not grow and the existing trees become too old. The second reason for the decline is caused by the parasitic brown-headed cowbird. The Kirtland’s Warbler does not recognize an imposter egg, consequently, they spend their time raising cowbirds. The cowbird eggs hatch before the host eggs hatch, get fed first, and grow quickly. Since the cowbirds are larger, they can keep the food from the host’s young. Prior to 1972 , each nest averaged one fledged bird, mainly due to cowbird parasitism. The result of cowbird population control has brought that number up to an average of three per nest. In 1998, Michigan’s Kirtland’s Warbler population was the highest recorded since 1951, with 805 singing males officially counted, compared to 733 in 1997, and 692 in 1996. Contributions to the increase in their numbers: (1) Restoration of their nesting habitat has been credited with increasing their population. The U.S. Forest Service, the U.S. Fish and Wildlife Service and the Michigan DNR, Department of Military Affairs, and wildlife biologists are annually maintaining nesting sites by a combination of clear cutting, controlled burns, seeding and tree plantings to mimic a forest fire. Approximately 150,000 acres of sandy highlands are set aside for the Kirtland’s by Roscommon, Atlanta, and Oscoda Counties. These areas are on a rotational plan to make sure the Kirtland’s, as well as other species of plants, songbirds and game animals have the habitat they require. Seventy percent of the nesting Kirtland’s were found in "created plantations". The goal is to have 2,000 birds and to sustain this number through the rotation of habitat. In 1998, over 3,500 acres of jack pine trees were planted on state and federal lands. These new areas should provide habitat for warblers in six to ten years. In 1972 the Fish and Wildlife service began (2) live-trapping cowbirds in an effort to control them in the Kirtland’s Warblers nesting areas. Before the trapping began, cowbirds parasitized 70% of the Kirtland’s nests. After the trapping, they parasitized approximately 3% of their nests, effectively tripling the Kirtland’s population. 4,000 cowbirds have been removed from this area annually. A further method of (3) managing their habitats is to close the nesting areas to the public. Since 1994, the Forest Service and DNR have lead tours daily from mid-May through early July. No dogs or taped birdcalls are allowed. The DNR, U.S. Forest Service, Fish and Wildlife Service, and Geological Survey have been involved with banding Kirtland’s Warblers for 13 years. Each bird that is captured in a mist net is weighed, checked for sex identification and banded. It is then taken back to where it was captured and released. This entire process takes five to 10 minutes per bird. Other species that are caught are released immediately. Contributions to the Nongame Wildlife Fund on your Michigan state income tax return help support the Kirtland’s Warbler recovery program.
Young Kirtland’s Warblers have been confirmed in the UP since 1996.
Last Update: Sunday, April 06, 2008
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