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 15 of 115

150 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 these two individuals appear in Figures 13a- b respectively. The primary song of the Virginia's Warbler is normally much more complex, although one population in Arizona exhibits songs characterized as being similar to that of the Orange-crowned Warbler (Olson and Thom- as 1999). Songs are usually comprised of 3-12 syllables (notes) of two to four different note types sung at a much slower rate and contain a variety of notes either up-slurred or down-slurred. Some of these can be simi- lar to the ending notes of the Colima War- bler's song, but none bear much similarity to the pattern in the trill of that species. Oth- erwise, note patterns exhibited by Virginia's Warbler appear more similar to other war- bler species, e.g., Nashville Warbler (Oreoth- lypis ruficapilla), Grace's Warbler (Setophaga graciae), and Prothonotary Warbler (Proto- notaria citrea; see Bryan et al. 1987) than to Colima Warbler. Initially, all Oreothlypis warblers observed and voice-recorded in the Davis Mountains were assumed to be Virginia's Warblers. However, review of our data suggests that vocally pure Virginia's were actually most abundant in Gambel Oak-dominated habi- tat found on higher ridges. There were birds in lower elevation habitat that exhibit songs similar to Virginia's, but plumage character- istics noted during those observations did not match pure individuals of that species or could not be adequately assessed. Examples of the song of some of the higher elevation Davis Mountains pure Virginia's Warblers (that were also visually consistent with Vir- ginia's) are presented in Figure 15a-c. For comparison, an additional five song cuts from four phenotypically typical Virginia's Warblers were obtained in the Guadalupe Mountains in June 2003, two of which are presented in Figure 16a-b. Additional recordings and spectrograms from singing Oreothlypis warblers observed and recorded in the Chisos Mountains of Big Bend National Park (n = 17) and adja- cent Mexico (n = 1) were analyzed on the xeno-canto website. All recordings of prima- ry song posted to xeno-canto are consistent with patterns (trill type songs) exhibited by Colima Warbler. Examples are presented in Figure 14a-c. The primary songs of suspected hybrid individuals can only be characterized as complicated, ranging from simple to com- plex. It can be comprised of only one syl- Spectrograms of Colima Warbler songs (14a) recorded 18 May 2009 in the Chisos Mountains, Big Bend NP, Brewster County, Texas by Andrew Spencer (cut XC34310); (14b) recorded 12 May 2014 in the Chisos Mountains by Arman Moreno (cut XC179361); and (14c) recorded 25 April 2007 in the Chisos Mountains by Daniel Lane (cut XC27380). 14a 14b 14c it is obvious that both morphological infor- mation and plumage descriptions are consis- tent with our findings from our prior field surveys on the Davis Mountains Preserve. Song Pattern Analysis The primary song of the Colima Warbler is often characterized as being most similar to that of the Chipping Sparrow (Spizella pas- serina). Among congeneric wood-warblers, it is more similar to the Orange-crowned Warbler (Oreothlypis celata) than to Virginia's or Lucy's warblers (Oreothlypis luciae) (Stein 1968, Wauer 1994). The song is comprised of a multiple note trill of approximately 2 seconds duration, with or without one to three sharp terminal notes that show on a sonogram as broad down-slurred notes. The trill can be simple or complex but is typi - cally comprised of one or two basic syllables or note types repeated in rapid succession at a frequency of 11-15 syllables per second, and usually increasing in amplitude in the middle or near the end. As is the case with most wood warbler song patterns, the syl- labic patterns found in each male's song is unique to that bird—only the frequency of notes exhibited varies. During the surveys conducted on the Da- vis Mountains Preserve from 1999 to 2006, 50 cuts of Oreothlypis warblers primary songs representing 23 different individuals were ob - tained. At the end of each song cut, informa- tion on plumage characteristics of each bird recorded was noted in the voice trailer along with other important facts such as date, time and location. Detailed analysis showed that only two of those recordings were consistent with Colima Warbler. The first was the sing - ing male discovered on 18 June 1999 in Tobe Canyon, which represented the first record for the Davis Mountains. Song spectrograms produced from those recordings confirmed it was singing a classic Colima-type song. The second individual was also singing a typical song pattern for the species. It was also en - countered and recorded in Tobe Canyon on 23 June 2001 (at an elevation of 6,750 ft.). It was, however, not photographed. The note patterns contained in this bird's song were clearly different than that of the 1999 bird, thus a different individual. Spectrograms of

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