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Kirtland's warbler (Setophaga kirtlandii ) [=Dendroica kirtlandii]
A pair of Kirtland’s warblers requires at least eight acres of dense young jack pine forest to nest, but often 30 to 40 acres is needed to raise their young. Their exacting requirements for nesting, as well as cowbird parasitism, caused a drastic decline in numbers and led the U.S. Fish and Wildlife Service to list the Kirtland’s warbler as an endangered species in 1967.
Endangered means a species is in danger of extinction throughout all or a portion of its range, while the less dire threatened designation means a species is likely to become endangered within the foreseeable future.
Until 1995 Kirtland’s warblers had only been known to nest in the northern part of Michigan’s Lower Peninsula. Today, they also nest in the Upper Peninsula, and since 2007, have nested in Wisconsin and Canada. They migrate from their nesting grounds to the southeastern coast of the United States on their way to wintering grounds in the Bahamas.
Primarily insect eaters, Kirtland’s warblers forage for insects and larvae near the ground and in lower parts of pines and oaks. They also eat blueberries.
Kirtland’s warblers nest only on the ground near the lower branches and in large stands of young jack pines that are 5 to 20 feet tall and 6 to 22 years old. The tree’s age is crucial, although biologists are not sure why. It is possible that the birds need low branches near the ground to help conceal their nests. Before the trees are six years old, the lower branches are not large enough to hide the nest. After 15 years, these lower branches begin to die.
Fires play an important role in forest ecosystems. For example, without fire, jack pine cones do not completely release their seeds. Suppressing forest fires prevented the natural establishment of new jack pine stands. Since Kirtland’s warblers will only nest in stands of young jack pines, the population dwindled dramatically before scientists realized that there is a role for fire in forest ecology — and in the Kirtland’s warbler life history.
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Find out about the Kirtland's warbler from Field Office biologists Dan Elbert, Chris Mensing and Christie Deloria.
Long-term Management for Kirtland's Warbler
As a conservation-reliant species, the Kirtland’s warbler will always be dependent on annual habitat management and control of parasitic cowbirds. Although recovery goals have been met, provisions for continued management must be ensured before Endangered Species Act protection can be removed for the Kirtland's. A first step is a Memorandum of Agreement signed by partner agencies.
Natural History and Regulatory Information
Kirtland's warblers build their nests on the ground in stands of young jack pine. The jack pines must be just the right height (about 5 to 16 feet tall) and the trees must be spaced to let sunlight through to the ground. Sunlight helps keep lower tree branches alive and bushy, hiding the nest beneath them. When the trees grow larger their upper branches block the sun, causing the lower branches to die. Grasses and other plants also become less dense. The warblers then must find other nesting areas. After nesting and raising their young, Kirtland's warblers migrate to the Bahamas where they winter in scrub thickets.
Recovery is the process used to restore threatened and endangered species to the point that protection under the Endangered Species Act is no longer needed.
Under natural conditions, Kirtland's warbler nesting habitat is produced by fire. Fire has always occurred in forests and jack pine trees are dependent on fire. Heat from fire is needed to open their cones to release seeds. Fire also removes plants that compete with jack pines for forest space and creates a bed of ash that helps the new seeds grow. Fires before the 20th century were more widespread in the jack pine plains of Michigan and created large nesting areas for the Kirtland's warbler. Modern habitat management is aimed at mimicking post-fire conditions. Prescribed fire, clearcutting, replanting, and cowbird control are some of the measures taken to restore Kirtland's warblers and their habitat. We work with the U.S. Forest Service, the Michigan Department of Natural Resources and other partners to recover and conserve Kirtland's warblers.
Last updated: September 21, 2016