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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12 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 amination of 911 specimens of the contend- ing taxa by Pyle at the American Museum of Natural History (AMNH), New York, the Museum of Vertebrate Zoology (MVZ), Berkeley, and the California Academy of Sciences (CAS), San Francisco. We apply the molt and plumage terminology of Pyle (2008) for long-distance migrant birds that undergo preformative and prebasic fight- feather molt on winter grounds, allowing that other interpretations are possible in these cases and should be further contem - plated (see Pyle and Reid, in press). Although many inter-taxon differences regarding timing, extent, location, and se - quence have been reported, specimen exam- ination for this paper indicates that the molt strategies of these shrike taxa are probably more similar to each other than has been understood thus far. Substantial individual variation in the extents of each molt, both prior to and following southward migrations (of varying distances within each taxon), coupled with an inability to trace the molts of individuals outside of captivity, appears to have resulted in various interpretations for a similar complex molting situation. We propose that molts and plumages within this shrike species assemblage are similar to those within certain shorebird genera (Calidris, for example) in which molt strategy varies as much or more by winter - ing latitude and breeding status of individu- als than it does by taxonomic relationships (Pyle 2008: 500-505). Trans-equatorial mi - subspecies of Red-backed Shrike (pallidifrons and/or kobylini) may represent clinally intro - gressed populations between these two taxa, as perhaps do grayer-backed individuals of Turkestan Shrike (sometimes referred to as subspecies karelini). By contrast, evidence from studies on the breeding grounds indi - cates that hybrids between Red-backed and Isabelline Shrikes are less common and more localized, and those between Red-backed and Brown Shrikes are rare, with mixed pairs usually disassociating before breeding (Kryu - kov and Panov 1980, Kryukov 1995, Kryu- kov and Gureev 1997, Panov 2009, Panov et al. 2011; A. Kryukov, pers. comm.). The contending taxa for the Mendocino shrike, based on range, migratory status, and appearance, therefore, include Red-backed Shrike, Turkestan Shrike, nominate popula - tions of Isabelline Shrike, and Brown Shrikes of subspecies cristatus, lucionensis, and confu - sus. Hybrids to be considered include those between Red-backed Shrike and all three of the above species. Among the Brown Shrikes, hybridism is limited to subspecies cristatus, as the breeding range of Red-backed Shrike is distantly allopatric with those of both confusus and lucionensis (Figure 4). We restrict further consideration of the Mendocino shrike's iden - tifcation to these six highly migratory taxa and the above three hybrid combinations. Molts, Plumages, Age, and Sex Shrikes of the Red-backed/Turkestan/Isabel- line/Brown species assemblage show three plumages within the frst molt cycle and two plumages in defnitive cycles, with sex- specifc differences beginning with the for - mative (post-juvenile) plumage. Thus, nine plumages can be recognized within each taxon, resulting in 54 plumages to consider among the six contending taxa noted above, not to mention those of hybrids. Fortunately, the Mendocino shrike showed a distinct black mask and little or no barring to body feathers from the outset (Figures 1-3), indi - cating a male within either the frst or de- fnitive cycle, and thus eliminating the most diffcult 42 of these possible plumages from consideration. Molts of these shrikes are complex, age and sex determination bear critically on identifcation (Dean 1982, Worfolk 2000), and the fact that the Mendocino shrike was undergoing molt of fight feathers and body feathers necessitates an attempt to untangle molt, age, and plumage variables before proceeding with taxonomic evaluation. A precise determination of feather generations for molted vs. unmolted fight feathers dur - ing the course of the shrike's documentary period is also needed to perform detailed assessments of wing and tail morphology (see below). The following interpretation of molts in these shrikes is based upon a syn - thesis of the literature (Medway 1970; Stre- semann and Stresemann 1971, 1972; Svens- son 1992; Cramp and Perrins 1993; Jenni and Winkler 1994; Worfolk 2000; Panov et al. 2011) as affrmed and updated by ex - Figure 7. Progression of primary and rectrix molt in the Mendocino shrike on 16 April. Note the mixed blackish and brownish patterns to the formative rectrices (as viewed from below) and the white patches at the bases of the primaries that extend beyond the primary coverts (see also Figure 13). Photograph by Mark Rauzon. r2 r4 r6 s5-s6 dropped s5-s6 dropped s5-s6 dropped r1 r1 r1 r2 r3 r3 r3 r2 r4 r4 r5 r5 r5 r6 r6 s4 s3 s4 s2 s3 s1 s2 s4 s 4 s3 p1 s1 s 3 s2 p2 p1 s s1 p3 p4 p2 s p1 p p2 p3 p3 p5 p4 p4 p7 p6 p5 p5 p6 p6 p8 p7 p7 p8 p8 p9-p10 dropped dropped p9-p10 p9-p10 dropped

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