Colima Warbler

Vermivora crissalis

(c) Greg Lavaty
  • PARULIDAE
  • Wood Warblers
  • 25,000

This large, mostly brown and gray warbler with a yellow rump lives in the mountains of western Texas and Mexico. As one of the least studied warblers in North America, very little is known about its population size and what threatens its survival.

Identification
A mostly brown warbler with a gray face, throat, and breast, white eye ring, orange crown (usually hidden), and yellow undertail coverts. Similar to the Virginia's and Nashville Warblers in appearance, but never has yellow on chest and is a darker brown.

Distribution and Population Trends
Breeds in the Chisos Mountains of western Texas and the Sierra Madre Occidental of northeastern Mexico. Breeding distribution is patchy. Winters on the Pacific slope of southwest Mexico. In both parts of its range it can be found in oak- and pine-dominated stands with a grassy ground cover. The Colima Warbler was thought to be restricted to Mexico until a specimen was collected in Texas in 1928. It was later confirmed that the warbler breeds in Texas. It is unclear if this represents a range expansion or was simply overlooked until then. The Texas population in the Chisos Mountains appears to be stable.

Ecology
Prefers chaparral regions between 1500m and 3600m in elevation where oak and pine are dominant and there is a grassy ground cover. Nests on the ground in leaf litter, grass, or hillside cavities, and is concealed from above by overhanging vegetation or rocks. Eats insects and their larvae from the air, by foraging on leaves, or by extracting them from oak galls. The Colima Warbler has been observed to adapt to weather patterns. In 1996, a snow and ice storm arrived after the Colimas returned to breeding territories and destroyed much of their food supply. The Colimas were observed to relocate to lower-elevation sites for breeding that year.

Threats
Heavily disturbed areas preclude the Colima Warbler, but habitat value appears to remain stable with light to moderate levels of disturbance from grazing, selective logging, and fires. Colimas have been observed breeding along hiking trails, but this appears to have little impact on nest success. The majority of Colima habitat is unsuitable for human activities, and it appears that it will remain so for the near future. Predation of eggs and young by feral dogs and cats from nearby villages appears to be a threat to this species.

Conservation
Big Bend National Park in Texas recognizes the importance of the site to the Colima Warbler by protecting and monitoring their breeding habitat. The Big Bend population has remained stable for the last 30 years and serves as an attractant for birders from late March to September. Control of feral dog and cat populations should be considered. The Mexican populations generally occur in areas that are difficult for people to get to and have little development, logging, or agricultural value. Thus, the Mexican population appears to be buffered from human impacts for the foreseeable future.

What Can You Do?
CIPAMEX, Audubon's BirdLife International partner in Mexico, has an Important Bird Areas program that is working to protect habitat for Colima Warbler and many other species. To learn more about Mexico's Important Bird Areas program and how you can help visit: http://www.wildbirds.org/news/mexico.htm

References
Beason, R. C. and R. H. Wauer. 1998. Colima Warbler (Vermivora crissalis). In The Birds of North America, No. 383 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.