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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22 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 taxa under consideration. However, the preformative molt occurring largely on the winter grounds and the relatively late timing to the fight-feather molt of the Mendocino bird supports the shrike's origin as one of the longer-distance migratory populations. The slightly later-than-normal and complete primary molt, despite a more northerly win - tering location, might be attributed to the vagrant status of the Mendocino shrike (see Howell et al. 2014, regarding similar molt in a vagrant sand-plover). In all four species, juveniles are heavily marked with black crescents, the result of V-shaped subterminal bars on both upper - part and underpart feathers (Figure 8). In males, formative feathers can either show or not show these crescents, perhaps based on early and later timing to the preformative molt, respectively, and some formative males with later molts can assume a duller expres - sion of defnitive alternate body plumage as well (Figure 8). Following the frst prealter - nate molt, frst-cycle males become much brighter and are very similar to defnitive alternate males in body plumage, although they may average slightly duller (Cramp and Perrins 1993; specimen examination; Figure 8). Defnitive basic males largely maintain alternate-like coloration, with the addition of brown fringing to basic feathers that subdues plumage tones when fresh. Defnitive basic males can also have a few dark crescents, es - pecially in the sides and fanks (Cramp and Perrins 1993, specimen examination). Although many males in frst or defni- Figure 13. The Mendocino shrike on 16 April (a,b), showing white to the bases of the formative primaries extending an estimated 2-4 mm beyond the primary coverts in the open wing. The primary showing the maximum extent of white beyond the primary coverts, p7, had not fully grown by this date (see Figure 7); once fully grown, more white would be expected beyond the coverts (see text for details). Note also the retained, brown, juvenile inner primary coverts contrasting with the outer three coverts, being replaced at the time these images were taken. Photographs by Mark Rauzon. 13b 13a tive alternate plumage are readily diagnosed to species and subspecies, these plumages within each taxon can show substantial vari - ation in the saturation, tone, and brightness of both upperpart and underpart coloration (Figures 9-10). For example, back coloration in Red-backed Shrike can vary from a bright brick-red to a dull reddish brown, and back coloration among Turkestan and Isabelline shrikes can vary in the shade of brown, to the extent of approaching or overlapping with each other in tone (Figure 9). The sides and fanks can vary substantially in color - ation in all taxa under discussion (Figure 10). These differences appear to refect both geographic and individual variation within each taxon, complicated further in some in - stances by hybridism or introgression. Intra-taxon variation in plumage color, coupled with different color saturations captured by different cameras, rendered it challenging to analyze the plumage of the Mendocino shrike for taxonomic placement. Assessment of its plumage was also hindered by shifting proportions of formative and frst alternate body feathering, requiring consid - eration of prealternate molt extent through- out the period of observation. When frst ob- served, the shrike showed subdued alternate- like patterns to the formative body plumage and few or no dark crescents (Figures 1-3). This perhaps suggests that it had under - gone a late preformative molt on the winter grounds that produced relatively defnitive- like formative plumage (see Pyle 2013b). In formative plumage, its crown and nape were mixed with grayish and brown feathering, its mask was dusky, its back, rump, and upper - tail coverts were dark pinkish rufous to cin- namon rufous with the rump contrastingly brighter and paler, and its sides and fanks were whitish washed pinkish buff (Figures 1-3). Juvenile rectrices were reddish to cin - namon (Figures 2-3, 6, 12a). As the Mendocino shrike molted during the period of observation, its crown became a brighter more-silvery gray mixed with some rufous on the nape, its mask became blacker and bordered above by an indistinct whitish supercilium, its underparts became whiter, and its sides and fanks were washed with brighter pale apricot-orange tones (Fig - ures 1-3). By the last week of observation, newly molted lower back and rump feath - ers appeared grayish (Figures 11-12). The uppertail coverts largely remained pinkish rufous (formative feathers), although dur - ing the fnal week of observation one or two mixed rufous-and-gray feathers appeared to be molting in. Incoming formative primaries were dusky blackish (Figures 6-7). When last photo - graphed, p2-p6 showed white bases that exceeded the tip of the primary coverts by an estimated 1-2 mm on the closed wing and by an estimated 2-4 mm on the open wing (Figures 7, 12-13). New formative ter - tials were blackish edged rufous and white (Figures 2, 11a). From above, the formative central rectricies were blackish brown, pal - ing slightly subterminally, and darkening to blackish terminally (Figures 2, 6, 11-12).

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