Kirtland's Warbler

Dendroica kirtlandii

Image by Ron Austing, US Forest Service
  • PARULIDAE
  • Wood Warblers
  • Passeriformes
  • Chipe de Kirtland
  • Paruline de Kirtland
Introduction

Aside from the Bachman's Warbler, which is likely extinct, the Kirtland's Warbler is the rarest warbler in nesting North America. In the breeding season, these birds are limited to the jack pine habitat of north-central Michigan. The bird might well have gone extinct if not for intensive habitat management and cowbird control measures.

Appearance Description

A fairly large warbler that often bobs its tail, the Kirtland's Warbler is a songbird measuring about 5.75 inches long with a 8.75 inch wingspan and weighing .48 ounces. The adult male is blue-gray above, yellow below, with sides and upperparts showing black streaking. His face is darker, contrasting with white arcs above and below the eye. Females are similar to males, but the upper parts are lighter and tinged with brown, and the yellow in the chin fades to a light wash below the breast.

Range Distribution

During the breeding season, the highly specialized Kirtland's Warbler is confined to the north-central region of Michigan in about 13 counties. Only 6 or so of these counties have suitable breeding habitat at any one time. The species' wintering range is known only to be in the Bahamas, where it occupies interior scrub and young forest.

In 2007, 2 singing males were observed in Ontario and 8 in Wisconsin.  In Spring 2007, a pair nested in Wisconsin, and another pair nested in Ontario.  The species had not bred outside Michigan since the 1940's, when this warbler bred in Ontario.

Habitat

This songbird nests only in dense stands of young jack pines. When trees reach about 22 feet, the birds no longer use them. This means that 2 or 3 years after a fire, the forest is occupied for about 20 years. Small clearings with maples, oaks, and aspen are also important ingredients. The wintering habitat in the Bahamas includes permanent scrub, scrub transitioning to forest, pinelands, and the border between mangrove forests and salt marshes.

Feeding

Hopping through the thick foliage of jack pines and young deciduous trees, the Kirtland's Warbler picks insects and their larvae from pine needles, twigs, and leaves. This summer diet includes flies, immature grasshoppers, moths, and sawflies. Occasionally, it will hover in front of a plant to pluck an insect from its surface. Ripe berries are also an important food source for adults and young. The winter diet includes many insects and small fruits.

Reproduction

In late spring, the male Kirtland's Warbler arrives before the female and establishes a territory of 8-20 acres, in a loose colony. When territories are being formed, males will attack each other, often in the air, grasping bills. Pairs are typically monogamous and produce one brood, but a second nesting is possible, if the first is lost or fledges early in the season. The female chooses a site under thick cover and uses her breast to depress a small bowl in the soft, sandy ground. She then pushes plant fibers and strips into the bowl, which is lined with grass, moss, and hair.

For about 2 weeks, the female incubates 3-6 whitish eggs, delicately marked with brownish spots. The male delivers food to her and the nestlings, which she keeps warm. In only 9 days, the young leave the nest and can fly weakly. The brood is split between the adults, and juveniles are fed until they are about 6 weeks old.

Migration

The Kirtland's Warbler migrates from the Bahamas to central Michigan to breed and probably makes the journey in one, long flight. Few of these warblers have ever been observed in migration. Spring migrants appear to reach Michigan in early May, and their route probably crosses over the Carolinas. Fall migration begins in late August and some adults linger on the breeding grounds into October.

  • 1,707 singing males; 4,500 overall
  • 1,707 singing males; 4,500 overall
  • Endangered
Population Status Trends

Kirtland's Warblers may have always been uncommon; however, in 1974 and 1987, the number of singing males was estimated to be only 167. Since 1990, the population has been increasing fairly steadily. In 1998, the number was estimated to be at its highest level until that time, with 805 singing males. The Michigan Singing Male Survey hit a new high in 2005 with 1,415 singing males according to the U.S. Fish and Wildlife Service (USFWS). In 2006, that number rose to 1,479, and in 2007 the number was 1,707. If we assume that every male has a female, then the best, albeit rough, population estimate for Kirtland's Warbler at the beginning of the breeding season is 3,400, and the best estimate after the breeding season is about 4,500.

Conservation Issues

The Kirtland's Warbler endures primarily because people maintain its habitat. In 2006, almost 4,000 acres were burned or cut to regenerate young jack pines. Outside the official management area, this habitat occurs in Michigan's Upper Peninsula and in parts of Wisconsin. Brown-headed Cowbirds have also been a serious problem. Prior to current control measures, more than half the nests were being parasitized. Habitat fragmentation, recreational cabins, and predators like cats are also threats.

Active land management for this species started in the late 1950's and intensified in 1974 when the Kirtland's Warbler was declared Endangered. Since 1975, a recovery team has directed conservation efforts in Michigan and neighboring states. Coordination with the government of the Bahamas began in 2002. This species is at the top of most conservation lists, including America's Top Ten Most Endangered Birds (2006).

The Recovery team estimates that at least 38,000 acres of proper habitat are needed each year and that this breeding area should be part of a 190,000 acre system. Today, many more acres and several new sites would be needed to reach that figure. Cowbird trapping has reduced parasitism rates from 70 percent to three percent, tripling the rate of warbler reproductive success.

The Kirtland's Warbler is a rising celebrity that attracts thousands of birders from around the world. Michigan Audubon has been leading a campaign to make this songbird the State Bird, a proposal that had still not been adopted by summer 2007. The participation of private landowners like the Plum Creek timber Company is vital to the creation of new habitat for this species and to its future.

What You Can Do

Between mid-May and early July, look for the Kirtland's Warbler by joining an official tour with the U.S. Forest Service near Mio, Michigan.

Become involved in the Important Bird Areas program in Michigan.

Attend the Kirtland's Warbler Festival, usually held during the second weekend of May, on the campus of Kirtland Community College in Roscommon, Michigan. Special tours are offered for seeing the warbler.

Support the conservation and restoration of the rare jack pine habitat, on which this warbler depends. Learn more about Michigan's efforts to grow the Jack Pine Ecosystem.

If you live in the area of north-central Michigan where Kirtland's Warblers breed, be sure to keep your cat indoors.

Find out about actions you can take including Audubon programs and activities.

More Information

Read more about Kirtland's Warblers in Wisconsin: "Discovery of Rare Bird Nest is Cause for Celebration," the USFWS press release for June 2007.

For more information on Kirtland's Warbler, including what you can do to help, contact the Michigan Department of Natural Resources, Wildlife Division, Natural Heritage Program, P. O. Box 30180, Lansing, MI 48909-7680. Kirtland's Warbler CONTACTS: Raymond Rustem, (517) 373-1263. 

Learn more about this species and other birds through these resources.

Natural History References

Mayfield, Harold F. 1992. Kirtland's Warbler. In The Birds of North America, No. 19 (A. Poole, P. Stettenheim, and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.

Olson, J. A. Species animal abstract for Dendroica kirtlandii (Kirtland's warbler). 2002. Michigan State University Extension. Michigan Natural Features Inventory. PO Box 30444, Lansing, MI., 48909-7944. 5 pages. Accessed 3 September 2007.

Sibley, David Allen. 2000. The Sibley Guide to Birds. Alfred A. Knopf, New York.

Conservation Status References

Endangered Species - Kirtland's Warbler. 2007 Nesting Season Summary.
U.S. Fish and Wildlife Service, Division of Endangered Species. Accessed 11 Nov 2007. 

Mayfield, Harold F. 1992. Kirtland's Warbler. In The Birds of North America, No. 19 (A. Poole, P. Stettenheim, and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.