North American Birds

VOLUME 70 NO2 2018

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

Issue link: http://nab.aba.org/i/1028840

Contents of this Issue

Navigation

Page 8 of 115

143 PRESUMED COLIMA x VIRGINIA'S WARBLER HYBRIDS IN TEXAS V O L U M E 7 0 ( 2 0 1 8 ) • N U M B E R 2 feet of elevation. Furthermore, they are lo- cated approximately halfway between the Guadalupe Mountains on the New Mexico border to the north and Big Bend National Park's Chisos Mountains near the Mexican border to the south. Prior to 1990, the Virginia's Warbler had only been documented as a breeding spe - cies in Texas in the Guadalupe Mountains (Oberholser 1974, Wauer and Ligon 1974, Johnson 1976). In the summer of that year, a casual survey of the higher elevations of the Davis Mountains by Steve Howell and Sophie Webb produced several territorial singing male Virginia's Warblers (Lasley and Sexton 1990). Follow-up surveys in June 1991 con - firmed the presence of multiple singing males in central portions of the range at elevations above 7,500 feet (Peterson et al. 1991). The Nature Conservancy acquired a sig- nificant portion of the upper elevations of the range in 1996, creating the Davis Mountains Preserve. More extensive surveys beginning in 1998 re-confirmed the presence of territo- rial Virginia's Warblers on the higher ridges, associated chaparral habitat normally found above 6,000 feet. The Chisos Mountains population represents the northernmost limit of the species' breeding range and com- prehensive surveys there have determined the maximum number of breeding birds in any given year to be 83 pairs (Tweit 2007). Little is known about breeding densities of this species in the mountains of Mexico. Prior to 1999 there was no known over- lap in the breeding distribution of these two species. Extensive surveys in the Davis Mountains beginning in that year have now revealed apparent direct breeding contact between these closely related taxa that has occurred long enough for a hybrid popula- tion to now dominate. The Texas status of the two species is well described and sum- marized by Lockwood and Freeman (2014). Status in the Davis Mountains The Davis Mountains are the most extensive mountain range in the Trans-Pecos Region of Texas (Bryan and Karges 2001), with ap- proximately 800 square miles above 5,000 Figure 3 • In the canyons Silverleaf Oak is more dominant. This is the habitat in which Colima Warblers and hybrids were found. Photo by © Kelly B. Bryan Figure 2 • This presumed hybrid adult male was captured in Madera Canyon on 21 May 2003. Plumage features are very similar to Colima Warbler, including large size, heavy bill, darker tail covert coloration, brown wash to the back and flanks, and a non-emarginated primary 6. Only wing chord and culmen length fall within the overlap range for a Virginia's Warbler. This individual audio-recorded: see Figure 17a for the song pattern. Photo by © Kelly B. Bryan.

Articles in this issue

Archives of this issue

view archives of North American Birds - VOLUME 70 NO2 2018