North American Birds

VOLUME 70 NO3-NO4 2019

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.

Issue link: http://nab.aba.org/i/1115839

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255 V O L U M E 7 0 ( 2 0 1 9 ) • N U M B E R S 3 / 4 RED-BACKED SHRIKE IN ALASKA Turkestan, and Brown shrikes. Again, the in- trinsic length of r6, or the distance between it and the tail tip, can be difficult to calculate from photographs, but ratios can produce better results. The ratio (length between r5 and r6) ÷ (length between r6 and the inser- tion point of the rectrices or tail base) has been found useful (Pyle et al. 2015). In the Gambell shrike, ratios of 0.096, 0.132, 0.148, 0.149, 0.153, and 0.161 were calcu- lated (fig 7C-D), with a mean of 0.140. The width of r6 also appeared to be similar to or slightly narrower than that of r5, with a somewhat broad tip (fig 7C-D). Age and Sex Proper aging and sexing of the shrikes in this complex is a very important first step Although actual distances between pri- mary tips are difficult or impossible to as- certain from photos, ratios may be more reliable as they rely less on the angle of the wing relative to the plane of the image. Pyle et al. (2015) found the ratio (length of p8 to p9) ÷ (length of p9 to the tips of the primary coverts) to discriminate Red-backed Shrike from Turkestan and Brown shrikes (Pyle et al. 2015). This ratio could be calculated from four images of the Gambell shrike as 0.126, 0.127, 0.131, and 0.149 (fig 7A-B), with a mean of 0.133. Another feature of primary morphology that differs among these shrikes is the number of primaries showing emargi - nation. Examination of several images indi - cates that p7–p9 were emarginated but that p6 did not appear emarginated (fig 3, 5, and 7B), although we believe such determination from the photos should be deemed tentative. The relative lengths and widths of the tail feathers, in particular, that of the outer rectrix (r6), also differ between Red-backed, past the tertials—not including the outmost two primaries (p9 and p10) that have tips falling beneath the others. This count de- pended on how spread the wing was. The shrike often sat with partially-spread wings (fig 1, 3, and 6) showing eight exposed tips (p1-p8), but when the wing was fully folded it appeared that six (p3–p8) or seven (p2- p8) tips fell beyond the tertials (fig 4). Due to variation in the wing spread in situ and the intrinsic length of the longest tertial (s7) among individuals, and due to wear and molt, a better means of assessing wing mor- phology is through the relative lengths of the outer primaries. Important to the iden - tification of Eurasian shrikes is the length of p9 relative to those of the other primaries. Several images clearly show the tip of p9 to fall about even with that of p6, those taken from behind showing it slightly shorter (fig 3) but those taken perpendicular to the wing angle showing the tips of p9 and p6 almost exactly even in length (fig 1 and 6). Figure 4. This photo of the Gambell Red-backed Shrike on 14 Oct 2017 captures many important characters: a low-contrast, rusty mask, distinct and extensive dark vermiculations both above and below, and a pale gray nape. Photo by © Clarence Irrigoo Jr.

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