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 21 of 179

T H E M E N D O C I N O S H R I K E 20 N O R T H A M E R I C A N B I R D S maries and the outer primary coverts (Figure 13). According to the molt terminology used here, it was thus completing the preforma - tive molt of fight feathers and had initiated the frst prealternate body-feather molt dur - ing the period of observation. Unmolted outer primaries and rectrices were narrow, tapered, and worn, and the new and growing feathers of these tracts were substantially duskier or blacker in appearance (Figure 6), indicating replacement of juvenile with formative feath - ers. Despite some plumage features suggesting defnitive basic plumage in early March, the body feathering changed coloration rather substantially (Figure 1), indicating transition from formative to frst alternate plumage as opposed to the more static appearance change between defnitive basic and defnitive alter - nate plumage in males. The bill was also dusky with a substantial pinkish base to the lower mandible throughout the period of observa - tion (Figures 2-3), further suggesting a frst- cycle bird for a male (Svensson 1992, Cramp and Perrins 1993). The frst prealternate body-feather molt had commenced by early April, as indicated by mixed worn and fresh feather generations visible in photographs, along with a shifting plumage appearance (Figures 1-3). Body- feather molts in birds generally proceed from head to rump and breast to vent (Jenni and Winkler 1994, Pyle 1997), and this is also refected in photographs of the Mendocino shrike. Molt of the head and upper back had largely completed but that of the lower back, suggests that primary molt had commenced around 12 March and would have completed around 8 May, barring suspended or arrested molt following the last observation. Replacement of secondaries and rectrices proceeded largely as described above. By 21 March, the central tertial (s8) was growing, and the remaining eight secondaries had not yet dropped, and by 16 April the inner two tertials (s8-s9) were new, s7 was 90% grown, s5-s6 had dropped, and the remaining sec - ondaries (s1-s4) were old (Figure 7). Given that this was the preformative molt (see be - low), we suspect that, at most, the s4 might have been replaced by the time the molt com - pleted, leaving p1 and s1-s3, along with most of the inner primary coverts, as retained ju - venile feathers, a pattern noted in specimens of frst-spring/summer shrikes of all four spe - cies. By 13 March, the four central rectrices (r1-r2 on each side) had apparently dropped, and by 21 March these were growing at about 50% of full length (Figure 6b). Sometime dur - ing this period, the right central rectrix was lost and, by 3 April, was re-growing at about 40% of full length, at which point the other three central rectrices had fully grown, the r3s were growing at about 20% of full length, r4- r5 had dropped, and r6 on each side of the tail remained. By 16 April, r1-r3 were full-length, and r4, r5, and r6 were growing, at 70%, 30%, and 20% of full length, respectively (Figure 7). Based on molt timing and replacement patterns, then, the Mendocino shrike was a frst-cycle bird, as confrmed by the retention of brown inner juvenile primary coverts, con - trasting with the replaced corresponding pri- rump, and uppertail coverts had not com- pleted by the time these areas were last photo- graphed, in mid-April. Plumage tones The variable molts and plumages of the shrike species assemblage considered here, coupled with molt-plumage interactions (see Pyle 2013b) and age/sex-specifc differences within each species, results in complex and variable plumages within each taxon (Dean 1982, Svensson 1992, Cramp and Perrins 1993, Le - franc and Worfolk 1997, Harris and Franklin 2000, Worfolk 2000, Panov et al. 2011). The following analysis is based on information from these references, with an emphasis on males in formative and fresh alternate plum - ages, as verifed by specimen examination by Pyle and extensive feld experience by Moores and Dunn (primarily with Brown Shrike). The timing and sequence of the preforma - tive and frst prealternate molts in the Men- docino shrike, described above, offer little direct elucidation as to its identifcation due to the similar overall but individually vari - able nature of these molts among the shrike

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