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.

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N O R T H A M E R I C A N B I R D S 142 Plumage Characteristics and Song Patterns of Presumed Colima X Virginia's Warbler Hybrids in the Davis Mountains of Texas Plumage Characteristics and Song Patterns of Presumed Colima X Virginia's Warbler Hybrids in the Davis Mountains of Texas KELLY B. BRYAN • 524 LIMPIA CANYON TRAIL, FORT DAVIS, TEXAS 79734 • KELLY.B.BRYAN@GMAIL.COM MARK W. LOCKWOOD • 402 EAST HARRET AVENUE, ALPINE, TEXAS 79830 • MWLOCKWOOD402@GMAIL.COM Abstract The 1996 acquisition of the upper elevations of the Davis Mountains, Jeff Davis County, Texas by The Nature Conservancy allowed for a modern and thorough inventory of the local avifauna. Surveys there in June 1999 documented the presence of a singing male Colima Warbler (Oreothlypis crissalis), the first documented US occurrence away from the Chisos Mountains. Since that time, a few more Colima Warblers have been detected, and the presence of a small breeding popula- tion of Virginia's Warblers (O. virginiae) has also been confirmed. Additional fieldwork revealed an apparently stable population of Oreothlypis warblers exhibiting plumage characteristics and song patterns intermedi- ate between Colima and Virginia's warblers. These birds were discovered in woodland habitat between 6,200-7,000 feet of eleva- tion. From 1999 to 2006, audio recordings of Colima Warblers, Virginia's Warblers, and intermediate birds were obtained. Presented here are song patterns of intermediate birds compared to recordings of Colima Warblers from the Chisos Mountains, Texas and of Vir- ginia's Warblers from the Guadalupe Moun- tains, Texas. Photographs of intermediate individuals provide potential qualitative evidence of variation in plumage characteris- tics. These data support the hypothesis that intermediate individuals represent a hybrid population that outnumbers either putative parental species in the Davis Mountains. Breeding Distribution The Virginia's Warbler (Oreothlypis vir- giniae) is primarily a bird of the Great Ba- sin Region and southern Rocky Mountains, breeding from eastern California through most of Nevada, southeastern Idaho, Utah, southwestern and central Wyoming, and the mountains of Colorado and the Black Hills of South Dakota, south across central and southeastern Arizona, central and southern New Mexico, and western Texas (Guadalupe and, probably, Da- vis Mountains). Breeding habitat consists primarily of montane, evergreen-oak woodlands and associated riparian woodlands normally found above 6,000 feet. In selected areas of the Guadalupe Mountains breeding densities were found to be as high as 16 pairs per 100 acres (Newman 1979). The entire Da- vis Mountains breeding popula- tion is estimated to be less than 100 pairs (Bryan and Lockwood, pers. obs.). The Colima Warbler (Oreoth- lypis crissalis) has a more restrict - ed breeding distribution, occur- ring from the Chisos Moun - tains in southwestern Texas south into northern portions of Mexico's Sierra Madre Oriental, including western and central Coahuila, western and south- ern Nuevo Leon, northeastern Zacatecas, northern San Luis Potosi, and southwestern Tam- aulipas (AOU 1998). Breeding habitat also consists of montane, evergreen-oak woodlands and Figure 1 • The Gambel Oak-dominated habitat on the ridgetops is favored by Virginia's Warblers. This photograph shows the upper slopes of the Davis Mountains. Photo by © Kelly B. Bryan

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