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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Figure 19. Specimen of a presumed Red-backed x Turkestan Shrike hybrid undergoing the preformative or defnitive prebasic molt, collected 5 January 1927 in Ethiopia (FMNH 83458). Features resembling the Mendocino shrike include the coloration of the head, back, tertial edging, and (especially) the underparts, and a pinkish-based bill. The rectrices were grayish with white patches at the bases that were not extensive enough for a pure Red-backed Shrike. The bird was completing molt when collected, with r6 still growing (precluding full analysis of tail morphology) but p8 and p9 fully grown, resulting in morphology suggesting this hybrid combination (see text). Three other specimens identifed as Red-backed x Turkestan Shrike hybrids are located at FMNH (200775-200777), which allowed further assessment of wing and tail morphologies of this hybrid combination (see text). Photographs by Josh Engle. 30 N O R T H A M E R I C A N B I R D S T H E M E N D O C I N O S H R I K E are about the same length (specimen examina- tion) and were used for this ratio rather than the tip of p10, as the length of p10 showed substantial individual variation relative to the primary coverts (see Cramp and Perrins 1993), leading to less consistent ratios within each taxon than those using the primary coverts. Similarly, the distances from the tip of r6 to the tip of r5 (c) and from the tip of r6 to its insertion point (d) were taken on specimens to compare with ratios of c/d in images (Figure 15). The distance from r5 to r6 rather than r1 to r6 (as in other studies) was used due to molt of one or the other of these rectrices during a large part of the observation period. The ratios a/b and c/d, calculated from 11 images of the wing and eight images of the tail of the Mendocino shrike (Figure 15), were all fairly consistent (Table 1b), indicating a de - gree of reliability to this method. They indi- cated that both p9 and r6 were long relative to the overall wing and tail dimensions, falling within the range of Red-backed Shrike mea - surements from specimens. Among the images of the Mendocino shrike, even those ratios at the maximum end of the range, indicating p9 and r6 to be relatively short, still fell within the range of Red-backed Shrike and the lower extreme of the range for Turkestan Shrike but outside of the ranges for the other taxa (Table 1b). Despite some probable inherent inaccura - cy in the calculation of ratios from images, we are confdent that the results of this exercise suggest the identifcation of the Mendocino shrike as a Red-backed x Turkestan Shrike over a Red-backed x Brown Shrike hybrid, which we would expect to show ratios well above those of Red-backed Shrike. The width of the juvenile r6 in images appeared about equal to those of other rectrices, both juvenile and formative (Figure 16), further suggesting Turkestan rather than Brown Shrike in the ge - netic make-up of the Mendocino shrike. Habitat and vocalizations On winter grounds, Brown Shrike tends to favor forest edges and large trees, whereas Turkestan and Isabelline Shrikes favor arid open country and edges of cultivated felds (Cramp and Perrins 1993). Habitats surround - ing the mouth of Alder Creek in 2015 largely 19a 19b 19c

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