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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152 N O R T H A M E R I C A N B I R D S PRESUMED COLIMA x VIRGINIA'S WARBLER HYBRIDS IN TEXAS Finally, a Colima Warbler recorded in the Chisos Mountains exhibited a note pattern type (Figure 19) very similar to that of the songs of individuals of both phenotypically Colima-like hybrids (see Figures 2 and 17a) and known Virginia's Warblers (see Figures 18a and 18b). Summary We have documented that the Davis Moun- tains of Texas represent the only zone of contact between breeding Colima and Virginia's Warblers. Furthermore, we have shown that the identification, plumage characteristics, song patterns, and spatial and habitat distribution of breeding Oreoth- lypis warblers there are much more complex than previously documented. Evidence pre- sented suggests that most birds found there are not pure Virginia's or Colima Warblers but, rather, intermediates between the two species in either plumage pattern, song pat- tern, or both, strongly suggesting recent and probably ongoing hybridization. To fully answer this question, additional re- search is needed, including DNA analysis of pure individuals and presumed hybrids. Any such effort will be especially challeng- ing because comparative Colima Warbler tissue samples are difficult to obtain due to the species' limited and remote distribution in the mountains of northern Mexico. We have attempted to provide a framework for further study of these birds in hopes that it will attract additional attention to this population. Extensive habitat changes occurred in central portions of the Davis Mountains range in recent years. One of the most severe droughts in recorded history oc- curred in 2011 and 2012 throughout much of central and west Texas. This drought, combined with three severe wildfires and extensive outbreaks of western pine-bark beetles in pine habitat that did not burn, resulted in a high-percentage loss of mature Ponderosa Pine and understory vegetation, especially oaks. Habitat alteration was ex- tensive in both Madera Canyon and Tobe Canyon, and was equally impactful to the higher ridges both east and west of Mount Livermore. Since much of the previously occupied Oreothlypis habitat has been al- tered, new surveys are needed to reassess population status. Hopefully, these birds will persist, and future work will help de- termine the exact status of these warblers. 16a 16b 17a 17b 17c Spectrograms of a Virginia's Warbler songs (16a) recorded 5 June 2003 along the Tejas Trail (7,700 ft. elevation), Guadalupe Mountains NP, Culberson County, Texas. Cut 026-A3 by Kelly B. Bryan; and (16b) recorded 7 June 2003 in The Bowl (7,900 ft. elevation), Guadalupe Mountains NP. Cut 027-A6 by Kelly B. Bryan. Spectrogram the song of (17a) a presumed Colima X Virginia's warbler hybrid recorded 21 May 2003 in Madera Canyon. Cut 024-B3 by Kelly B. Bryan, (17b) of a presumed Colima X Virginia's warbler hybrid recorded 19 May 2001 in upper Tobe Canyon. Cut 014-A3 by Kelly B. Bryan; and (17c) of a presumed Colima X Virginia's warbler hybrid recorded 11 June 2005 in Madera Canyon. Cut 036-A7 by Kelly B. Bryan.

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