Kirtland's warbler has extremely restrictive breeding requirements, leading to its scarcity.
Kirtland's Warbler Population Gradually Increasing
Always a rare bird, Kirtland’s warbler wasn’t described by scientists until 1851. Its scarcity is a product of extremely restrictive breeding range requirements. It breeds only in dense stands of 5-20 year old jack pine trees (Pinus banksiana) with sandy soil and undergrowth sufficiently dense to hide its nest.
Until 1996, it bred only in a 500 square mile region of central Michigan, though populations now also breed in Wisconsin and Ontario. Every fall, the warbler migrates south to the Bahamas, returning north to mate in May, the males arriving shortly before the females. A large percentage of yearlings disappear every year, though it is unclear whether in the winter range or along the migration route.
Although the Kirtland’s warbler is listed as Endangered in the United States, its numbers have gradually increased since the mid 20th century. More than 150,000 acres are set aside for the bird in Michigan, and a partnership of U.S. and Bahamian agencies, including The Nature Conservancy, helps protect its winter range.