The endangerment of Kirtland’s Warblers is attributed to two factors: their requirements for nesting and cowbird parasitism. They nest only in stands of young jack pines, a habitat that exists only briefly after forest fires. Currently, their nests are found in just a few counties in Michigan's northern Lower and Upper peninsulas, in Wisconsin and the province of Ontario. An excellent description of the effect of cowbird parasitism on the size of the population of Kirtland’s Warblers and the efforts to control the number of cowbirds can be found by clicking on the link below.
