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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147 V O L U M E 7 0 ( 2 0 1 8 ) • N U M B E R 2 PRESUMED COLIMA x VIRGINIA'S WARBLER HYBRIDS IN TEXAS to be larger than Virginia's Warbler, although this was sometimes difficult to accurately assess through field observation. These "in- termediate" individuals also differed from pure Virginia's Warblers by exhibiting more brownish coloration on the back and flanks. The tail coverts ranged from the typical yel- low of Virginia's Warbler to slightly darker orange-yellow, but not approaching the deep golden-yellow coloration of pure Co- lima Warblers. Breast coloration was also variable, with most individuals lacking any yellow, but a few did exhibit yellow breast patches, including some that were otherwise more Colima-like in other aspects. An effort was made to capture some ter- ritorial males and examine these individuals. On 12 July 2002, two birds were captured in a mist net by deploying a decoy on a stick that was accompanied by song playback. These birds were chosen at random in Tobe Canyon and were near the location of the first Colima Warbler discovered in 1999. A third individual was captured 21 May 2003 in Madera Canyon, below its confluence with Tobe Canyon. Prior observation of that male had revealed its plumage to be more Colima-like but its song to be unlike Vir- ginia's or Colima. It was this bird, first noted on its territory in the spring of 2000, which convinced the authors that the two species could be hybridizing (Figure 2). All three were examined, measured, banded, photo- graphed, and then released; morphomet - rics and descriptions of important plumage characteristics are presented in Table 1 and are compared to available information previ - ously published for both species (Oberholser 1974, Curson et al. 1994, Pyle 1997, Benson and Wauer 2013). We interpret the presence of intermediate plumage characters and/or a combination of Virginia's and Colima morphological data to represent hybrids between Virginia's and Colima warblers. The majority of suspected hybrids observed in the field and examined Table 1 • Published summaries of morphometrics and plumage characteristics of male Virginia's and Colima warblers compared with three male birds captured in the Davis Mountains in 2002-2003. Virginia's Warbler Pyle (1997) BNA (2013) BLOT (1974) Curson et al. (1994) Wing chord (mm) 57-66 56-65 (60) 58.9-62.5 (61.2) 58-67 Tail length (mm) 43-50 44-50 (47) 46.7-51 (48.5) 41-50 Culmen length (mm) 8.9-10.9 8.9-9.9 (9.4) 8.9-10.9 (9.9) 8.9-10.8 Weight (g) 7.8 6.5-10 (8.1) 7.1 7-9 Emarginated P6 Yes Yes yes yes Yellow on breast most birds always yes yes Upper tail coverts -- greenish yellow sulphine yellow greenish yellow Under tail coverts -- greenish yellow gamboge yellow yellow Back no brown gray brownish gray pearl-gray Flanks whitish gray smoke gray gray Colima Warbler Pyle (1997) BNA (2013) BLOT (1974) Curson et al. (1994) Wing chord (mm) 60-69 60.5-68.5 (65) 62.5-67.6 (64.5) 58-68 Tail length (mm) 50-57 51-61 (55.5) 52.6-57.9 (55.3) 52-56 Culmen length (mm) 10.7-11.9 10.5-12 (11.4) 10.9-11.9 (10.4) 10.5-12 Weight (g) 9.7 8-11.5 (10) -- 8-11.5 Emarginated P6 no no no no Yellow on breast sometimes rarely no sometimes Upper tail coverts -- yellowish orange citrine yellowish olive Under tail coverts -- yellow-orange analine yellow yellowish buff Back grayish brown olive-brown brown/olive dark grey-brown Flanks brown buffy brown brownish olive brown Captured birds 12 July 2002 12 July 2002 21 May 2003* Character Key** Wing chord (mm) 64.5 62.5 59.5 Virginia's Tail length (mm) 58.5 54 52 Either Species Culmen length (mm) 10.3 10.3 10.8 Colima Weight (g) 9.8 10.2 10.0 Emarginated P6 yes yes no Yellow on breast yes no no Upper tail coverts yellow yellow brownish-yellow Under tail coverts yellow-orange yellow-orange yellow-orange Back dark gray dark gray Yellow-olive Flanks olive-gray gray buffy brown Linear measurements in millimeters (mean) *See Figure 1 for a hand-held photograph of this bird **Based on data from published literature Figure 8 ( opposite , top ) • Adult female Virginia's Warbler, captured and banded (2240-16486) on 9 June 2017 in upper Limpia Canyon. Measurements and plumage characteristics all within range for Virginia's Warbler. Photo by © Kelly B. Bryan. Figure 9 ( opposite , bottom ) • Adult male presumed hybrid warbler, captured and banded (2240-16471) on 18 May 2017 in upper Limpia Canyon. Note the brown tones in the flanks and back but bright yellow in the tail coverts. Most measurements within the overlap range for each species. Photo by © Kelly B. Bryan.

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