North American Birds

VOLUME 69 No1 2016

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 28 of 179

T H E M E N D O C I N O S H R I K E 27 V O L U M E 6 9 ( 2 0 1 5 ) • N U M B E R 1 viated in Isabelline Shrike than in Turkestan Shrike, less often meeting across the forehead (Panov 2009, Panov et al. 2011). However, study of specimens and images indicates over - lap between the two species in this feature and that photographic effect can make this diffcult to assess in images (e.g., Figures 2-3). This mark in the Mendocino shrike therefore seems equivocal in respects to the identifca - tion of either Isabelline or Turkestan Shrike infuence. Overall, we believe that the plum - age of the Mendocino shrike would fall within the range of variation shown for Red-backed x Turkestan Shrike hybrids in Figures 17.1 and 17.7 of Panov et al. (2011), and its relatively dark formative and frst alternate feathering would be unlikely to be seen in a Red-backed x Isabelline Shrike hybrid. However, given a number of complicating factors, the plumage-based evidence alone is not strong enough for identifcation in the case of the Mendocino shrike, other than to conclude that Red-backed Shrike genes are clearly involved. Extensive variation within cristatus Brown Shrikes could result in a re - combination (albeit unlikely) of plumage features that ft characters of the Mendocino shrike not contributed by Red-backed Shrike genes. This may especially be the case since phenotypic plumage expression by hybrids can show any combination of parental phe - notypes and occasionally contradictory plum- age patterns atypical of either parental species (Graves 1990, 1996; Rohwer 1994, Rohwer et al. 2000), perhaps representing ancestral character states no longer found in either parent. While all plumage features could be considered intermediate between Red-backed and Turkestan Shrikes, we cannot claim that any plumage feature is necessarily contradic - tory to a Red-backed x Brown Shrike cross, including the extent of white at the bases of the primaries. Furthermore, had the Men - docino Shrike originated from the Altai Re- gion of south-central Russia, where hybridiza- tion between Red-backed and all three other shrike species is known to occur (Figure 4), there is a possibility that it was comprised of genetic recombination from three or even all four species. Therefore, other variables beside plumage need to be considered in the identi - fcation of the Mendocino shrike. Size, structure, and fight feather morphology All of the taxa under consideration for the Mendocino shrike show roughly the same body size (Worfolk 2000). Thus, feld de - scriptions of the Mendocino bird, as vari- ously being about the size of a Loggerhead Shrike (L. ludovicianus) to the size of a Black Phoebe (Sayornis nigricans), are not helpful for identifcation. Bill size is larger and deeper in the Brown Shrikes than in the other three species (Svensson 1992, Cramp and Perrins 1993, Worfolk 2000), and most observers and those commenting on posted photographs thought that the bill of the Mendocino shrike appeared too small, stubby, and with a lower mandible too straight (rather than convex) for and sexes. Only one specimen of Red-backed Shrike was examined that had white extend - ing >3 mm beyond the primary coverts (MVZ 108600, collected in Czechoslovakia). By con - trast, in the Turkestan and Isabelline Shrikes combined, a white patch was present on all birds, it extended beyond the primary coverts in 91% of specimens, and it extended >3 mm past the primary coverts in 79% of specimens (n=33). Although the white patch extends slightly farther beyond the primary coverts when the wing is partially open than when it is closed (Cramp and Perrins 1993, specimen and photograph examination), on balance we believe that the extent of white in the prima - ries on the Mendocino shrike, estimated to be >3 mm past the primary coverts on a partially spread wing once molt would have completed (Figures 12c-d, 13), is more likely to be ex - pressed in a hybrid between Red-backed and either Turkestan or Isabelline Shrikes than in a hybrid between Red-backed and nominate cristatus Brown Shrike (but see Figure 19). Plumage features that favor Turkestan over Isabelline introgression for the Mendocino shrike include the darker brownish tone to the upperparts, the apricot underpart coloration not extending to the auriculars and resulting in a distinctly defned white throat, the indistinct whitish supercilium (lacking or less distinct in both Red-backed and Isabelline Shrikes), the richer rufous tones in the bases of the forma - tive rectrices, and the white (rather than buff) coloration in the bases of the primaries (Table 1a). The black mask tends to be more abbre -

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