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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Page 13 of 115

148 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 in-hand exhibit plumage characteristics in - termediate between the two putative paren- tal types. The overall body plumage is darker than the gray of a typical Virginia's Warbler, with a brownish wash on the flanks and back. The brown tones on these birds were sometimes not readily apparent except at close range and under good viewing condi- tions, giving the birds a more Virginia's-like appearance (Figure 4). The yellow tail co- verts and lighter gray head and underparts plumage also contribute to a more Virginia's- like appearance (Figures 5 and 6). In-hand examination allows for a better assessment of the extent of brown coloration on the flanks and back of intermediate birds (Figures 7); however, it is known that fall birds in fresh basic plumage are known to exhibit much browner plumage coloration. Spring birds in-hand ran the gamut from birds that were obviously pure Virginia's (Figure 8) to pre- sumed hybrid birds (Figure 9). Differences between presumed female hybrids and pure Virginia's Warblers are more subtle (Figure 10). Smaller numbers of presumed hybrids are much more similar to the pure parental types but are still intermediate in some char- acters. Most such individuals are more Vir- ginia's-like (Figure 11), but a few are more Colima-like as is the bird in Figure 2; these birds may represent back-cross hybrids. Between 2000 and 2012 more than 25 territories of presumed hybrids were lo- cated within the elevation range previously described. The majority of these birds ex- hibited similar plumage characteristics with gray body plumage similar in coloration to Virginia's Warbler. All birds had brown col- oration of varying intensity on the flanks and back. All appeared to be slightly larger than a typical Virginia's Warbler, but direct comparison was not possible. Adult females, fledglings, and a few active nests were also observed. The intermediate birds far out- numbered "pure" Virginia's Warblers in the Davis Mountains, and only a few "pure" Figure 10 • This individual was in close association with a territorial male in Silverleaf Oak in Upper Limpia Canyon on 7 May 2010 was likely a female. Presumed hybrid based on a brown wash on the flanks and pale yellow under tail coverts. Photo by © Mark W. Lockwood. Figure 11 • This singing male in Gray Oak habitat present in Tobe Canyon on 7 May 2011 is presumed to be a backcross hybrid based on the much stronger resemblance to a pure Virginia's Warbler, but with a strong brown wash on the flanks and back, and orange tail coverts. Photo by © Mark W. Lockwood.

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