One of the least studied North American warblers, the Colima Warbler breeds only in the Chisos Mountains of western Texas and the Sierra Madre Oriental of northeastern Mexico. It winters on the Pacific slope of southwest Mexico in lush western montane forests at elevations between 1,500 and 3,600 m. Both the breeding and the wintering habitats are dominated by oak (Quercus spp.) and pine (Pinus spp.) with grassy ground cover. This warbler forages on insect larvae gleaned from foliage or extracted from oak galls, but it also hawks insects from the air and picks up caterpillars from the ground. Its nest is well concealed on the ground amid litter or grass and shaded by overhanging vegetation.
The Colima Warbler is closely related to Nashville Warbler (O. ruficapilla) and Virginia's Warbler (O. virginiae), but it is larger and browner than either of these 2 species. Named for Colima, Mexico, where the type specimen was collected (although the area around Colima seems to be peripheral to its major wintering grounds), its distribution during the early part of the twentieth century was thought to be restricted to Mexico. On 20 July 1928, however, Frederick M. Gaige collected the first U.S. specimen, an adult male, in the Chisos Mountains of the Big Bend area of Texas (Van Tyne 1936). The first recorded nest of the species was discovered by Josselyn van Tyne (Van Tyne 1936) in 1932, 43 years after the first specimen was collected. He was working at Boot Spring in the Chisos Mountains of Texas when a female Colima Warbler, carrying nest material, appeared nearby.
A rare but locally common species, the Colima Warbler has been studied recently in Texas by Wauer (Wauer 1979, Wauer 1994) and in Mexico by Lanning et al. (Lanning et al. 1990). In spite of these studies, little is known about the behavior and ecology of this warbler during its migration and nonbreeding season, or even about its breeding at locations outside the Chisos Mountains of Texas.