Kirtland’s Warbler
The Jack Pine Warbler is Very Rare and Faces Many Threats
Kirtland's Warbler, Dendroica kirtlandii, has a tiny habitat and almost became extinct. Conservation measures have brought it back in Michigan, USA.
Kirtland’s Warbler, Dendroica kirtlandii, (also known as the Jack Pine Warbler) has a summer range that is confined to the jack pine stands of Michigan, Wisconsin and southern Ontario, breeding only in central Michigan. Its winter range is equally limited: the Bahamas, Turks and Caicos, and Hispaniola. With such a small habitat, Kirtland’s Warbler was probably never a common bird, but this large warbler declined to only about 400 individuals before efforts to save it turned things around. Saving the Jack Pine Warbler required a multi-pronged approach.
Restoring jack pine habitat
Kirtland’s Warbler nests only in jack pine stands, and then only in extensive stands that are from six to about fifteen years old where the trees grow in dense clumps with lots of small open spaces. The birds nest on the ground under the boughs of these young trees—when the trees reach a height of about five metres (16.5 feet), the warblers start to move out.
Jack pines have a life history that is intimately tied to fire—the cones of this species only open when fire sweeps through the stand, burning the mature trees and reseeding the dry sandy soil where the trees thrive. Without fire, the jack pines aren’t renewed and this, along with logging, accounts for significant habitat loss for Kirtland’s Warblers. When people started suppressing forest fires, the young jack pine stands dwindled.
In 1957 Michigan began to manage its jack pines in order to provide sufficient acreage of young stands for breeding Kirtland’s Warblers on a rotational basis. Today, there are about 140,000 acres of jack pines, with about 38,000 acres at the right stage for the nesting birds.
Controlling Brown-headed Cowbirds
Kirtland’s Warbler nests are susceptible to parasitism by Brown-headed Cowbirds, nest parasites that lay their eggs in the nest of another species and leave the host species to raise their chicks. In the case of Kirtland’s Warbler, warbler chicks don’t do well when they have to compete with larger cowbird chicks for food. In 1972, about 70 percent of Kirtland’s Warbler nests contained cowbird chicks, and less than half of the warbler chicks were surviving.
Trapping and euthanizing Brown-headed Cowbirds in Kirtland’s Warbler habitat (about 4000 cowbirds each year) has reduced the nest parasitism to less than 5 percent, and the population of Kirtland’s Warblers has increased from a low of about 400 to about 2000 birds. In addition, the warbler is expanding its range and has now been observed nesting further north in Michigan and also in the Canadian province of Ontario.
Conserving the winter range
Kirtland’s Warblers spend about eight months of each year in their winter range; therefore, any effective conservation effort must include protecting the birds’ winter habitat. Cooperative projects are still working to identify and protect the habitat that the warblers need in the south.
Other threats
Kirtland’s Warblers migrate by night, and thus face losses due to collisions with towers, tall buildings, and wind turbines.
Sources:
“Kirtland’s Warbler.” Cornell Laboratory of Ornithology: All About Birds.
“Kirtland’s Warbler (Dendroica kirtlandii).” Michigan.gov Department of Natural Resources.
