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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258 N O R T H A M E R I C A N B I R D S RED-BACKED SHRIKE IN ALASKA for Alaska and North America (Gibson and Withrow 2015, Pyle et al. 2015). As sum - marized by Worfolk (2000), Brown Shrikes "show the longest and deepest bill, the short - est wing, and the longest, narrowest, and most graduated tail," (fig 8) in combination creating a different impression than that shown by the Gambell shrike. Brown Shrike appears to show a larger head and longer- and narrower-tail than does Red-backed Shrike, and often (but not always) they have an obviously shorter primary projection be - yond the longest tertial. They have a subtly deeper-based bill, often with a somewhat convex rather than straight lower mandible, and grayer coloration at the base (fig 8). The boldness of the mask and the dark- ness of the lores are both highly variable in Brown Shrike, with the assumption that males tend to show more extensive and blacker face-masks and lores than do females (cf. fig 8). In only a few, exceptional indi- viduals, however, does this mask show rusty tones, as obviously shown by the Gambell bird (fig 1–6 and 10A). As shown in fig 8, Brown Shrikes lack the contrasting grayish nape typically shown by Red-backed and the Gambell bird. Typically, the underparts of juvenile Brown Shrikes are washed with light buff (including on the central breast and belly), unlike the Gambell bird. First-fall Brown Shrikes showing many of these char- acters have been seen previously at Gambell (fig 9 and 10B). Many of the single first-fall plumage characters shown by the Gambell Red-backed Shrike could be shown by some Brown Shrikes, but the combination of all these characters is outside the range of most or all Brown Shrikes. Brown Shrikes have a shorter primary projection, typically showing ca. four or five visible primary tips on the closed wing and six on the partially open wing (fig 8), whereas Red-backed—and the Gambell bird—typically show six or seven tips on the closed wing and up to eight when the wing is partially open (fig 1-4 and 6-7). The tip of p9 falls between those of p4 and p5 in Brown Shrike, whereas that tip is clearly longer in the Gambell shrike, falling about equidistant with the tip of p6 (fig 7A-B). The ratio of p8- p9/p9-primary coverts ranges from 0.233– 0.313 in nominate cristatus Brown Shrike and this ratio ranges from 0.090–0.155 in Red-backed Shrike (Pyle et al. 2015). This ratio varied from 0.126–0.149 (mean 0.133) in four images of the Gambell bird, nicely within the range of Red-backed Shrike but well outside that of Brown Shrike. Figure 8. A first-year Brown Shrike, South Korea, 3 September 2003, showing typical features of the nominate subspecies. Compared to first-fall Red-backed Shrikes and the Gambell bird, note the shorter primary projection (six primary tips visible on a partially opened wing), lack of gray in the nape, the bolder, blacker face-mask, and the grayish base to the bill. Photos by © Nial Moores Figure 9. The sixth fall record, and seventh overall, of Brown Shrike at Gambell was established by this individual on 20 September 2018. In comparison to Red-backed Shrike, it shows a larger, thicker-based bill with a grayish (rather than yellowish) base and slightly convex lower mandible, as well as a blackish (rather than rusty-brown) auricular patch. Photo by © Michael Schall

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