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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151 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 lable (note) type sung at a slow pace (like a short warble). However, in some cases, one to three sharp ending notes can create su- perficial similarity (both audibly and on the spectrogram) to the song Colima Warbler. If these birds have a predominately learned song, as is the case with almost all wood warblers that have been studied (Kroodsma 2005), then it makes sense that hybrid indi - viduals found in the Davis Mountains based on number of breeding individuals of each species, have a better chance of singing like a Virginia's than a Colima. To what degree genetics play in song ontogeny in this popu - lation is unknown and needs further study. In at least one species of wood warbler, the Prothonotary Warbler, development of final song pattern by second-year males is not the result of "learning" from neighboring territo- rial males (Bryan et al. 1987). Interestingly, playback to hybrids of their own voice almost always produced an ag - gressive and vocal response, whereas there was little or no response by hybrids to play - back of recordings of either "pure" species from the Davis Mountains. Table 2 presents the basic song characteristics of hybrids com - pared to those of the two parental species. Examples of sonograms from presumed hybrids are presented in Figures 17a-17c. The first individual presented here was a male first noted on territory and recorded in Madera Canyon on 7 May 2000, subse- quently recorded on ten occasions over the next three years on the same territory (Fig- ure 17a), and eventually (on 21 May 2003) captured and banded (color banded) so that plumage characteristics could be carefully examined. Although the note pattern type found in the bird's simple song (an inverted "V") was similar to note patterns found in at least three other male Virginia's Warblers, phenotypically the bird was very similar to 15a 15b 15c Table 2 • Basic song characteristics of presumed hybrids compared to Virginia's and Colima warblers Virginia's Warbler Colima Warbler Presumed Hybrids Syllable types – main song 2-4 1-2 1-3 Number syllables/second 5-7 11-15 4-8 Total syllables/song 9-14 15-23 5-12 Ending notes 0 0-3 0-2 Total length of song 1.4 – 2.0 seconds 1.7 - 2.2 seconds 1.3 – 2.3 seconds Frequency – main song 3.0 – 7.2 kHz 3.9 – 6.0 kHz 3.0 – 7.2 kHz Frequency – ending notes 0 3.0 – 7.0 kHz 3.5 – 6.7 kHz a Colima Warbler (see Figure 2). A second presumed hybrid individual presented here was a singing male noted on territory in up- per Tobe Canyon on 19 May 2001. This indi- vidual was studied by multiple observers as it foraged in a Gambel Oak-pine woodland at the lowest extent of that habitat. All observ- ers agreed that, based on appearance, this bird was consistent with a Colima Warbler. However, the song pattern (Figure 17b) did not match Colima Warbler. It did include a short—but slower—trill in the middle of the song but the other note pattern exhibited in its song was more similar to a Colima's end- ing note. A third individual that was identi- fied in the field as a Colima Warbler based on plumage characteristics, exhibited a song pattern totally unlike the species or the two examples above. It is obvious that the spec- trogram is not that of a Colima Warbler and is more like the patterns sung by Virginia's. Figure 17c shows this song pattern. Two additional individuals that were iden- tified in the field as Virginia's Warblers exhib- ited a song type similar to Virginia's (Figures 18a and 18b) but which included a note and pattern-type at the end of the song similar to that of a phenotypically very Colima-like hybrid (see Figures 2 and 17a). Both of these birds were located in upper elevation habitat. Spectrograms of a Virginia's Warbler songs (15a) recorded 22 May 2003 along the Limpia Chute Trail area. Cut 025-A6 by Kelly B. Bryan; (15b) recorded 19 June 2000 in upper Red Oak Canyon. Cut 007-B11 by Kelly B. Bryan; and (15c) recorded 20 May 2001 on the NE slope of Mount Livermore. Cut 014-A6 by Kelly B. Bryan. All recordings are from locations in the Davis Mountains Preserve, Jeff Davis County, Texas.

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