Kirtland’s Warbler was one of the most endangered birds in the United States no more than thirty years ago. It nested only in immature, burnt-over jack-pine forests in northern Michigan. This situation describes one of those places where fire has had a place for maintaining critical habitat. “Pioneer” habitat was more abundant at one time in forests where nature had to start over after fire in a process called ecological succession. European settlers generally attempted to stop forest fires, probably unwittingly decimating a bird they may not have noticed.
The first one was discovered in 1851 in Ohio, and only in 1903 was the nesting ground located. Periodic fires kept the stands dense and uniform, less than about fifteen feet tall, with dense ground vegetation to hide their nests made of grass and pine needles, containing four brown-dotted white eggs.
The Endangered Species Act has funded efforts to maintain the bird’s habitat. Unfortunately, the population has also been invaded by Brown-headed Cowbirds, which lay eggs in the warbler’s nest, hatching into large, murderous offspring, rendering the warbler’s reproductive efforts in vain. Furthermore, Kirtland’s Warblers winter far away in the Bahamas. Sometimes, the birds may be seen in areas of the Midwest and East during migration.
There are now estimated to be more than 3,600 pairs of Kirtland’s Warblers, most on the Kirtland’s Warbler Wildlife Management Area in northern Lower Michigan. They need at least 40, and probably 100, acres of proper habitat to breed successfully. Some are also in Wisconsin and Ontario. The species is less endangered now, but not yet “out of the woods.”
The scientific name of Kirtland’s Warbler is Dendroica kirtlandii, being part of a large genus of the very large warbler family. The song goes from low to high-pitched flip lip lip-lip-tip-tip-CHIDIP, and is notably musical, as expected from the family name. The bird is just over 5 inches long, dark gray above, small dark spots on pale breast, and often with an interrupted white eye-ring. Males and females are similar in appearance. Of the 100+ species of wood warblers, or Parulidae, 52 species breed in North America. The majority of them breed in northern forests and winter in the tropics, meaning that most Americans see them only in migration. In the spring, when they have breeding plumage, they are brightly colored and relatively easy to identify. However, they molt before migrating south again, giving rise to the notorious “fall warbler” problem for birders when identification hallmarks largely disappear.
With many species summering in the same coniferous forests there is potential competition, but the various species feed in different specialized niches. Some hunt insects near the ground, others near the tops of trees; some look for insects close to the trunk, and others farther out in the branches. This “divide and conquer” approach to each getting its needs for life, is called resource partitioning.
Good references for identification of the many warblers include National Audubon Society: Field Guide to North American Birds (Alfred A. Knopf, Inc., New York, 1998) by John Bull and John Farrand, Jr., and National Audubon Society: The Sibley Guide to Birds (Alfred A. Knopf, Inc., New York, 2000) by David Allen Sibley.
A good resource for general information about birds is The World Atlas of Birds (Sir Peter Scott, ed., Crescent Books, New York, 1974).
