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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33 V O L U M E 6 9 ( 2 0 1 5 ) • N U M B E R 1 T H E M E N D O C I N O S H R I K E than the ratios calculated from images of the Mendocino shrike (Figure 15a, Table 1b). The bills of these seven hybrid shrikes also appear larger and stouter than those of the 28 hybrid shrikes from Kazakhstan and the Arabian Pen - insula, as well that of the Mendocino shrike (compare Figures 2-3 with Figures 18-21). Both plumage and structural features thus suggest that hybrids from Kazakhstan and the Arabian Peninsula are primarily Red-backed x Turkestan Shrikes, whereas those from Ma - laysia and Japan are primarily Red-backed x Brown Shrikes, as generally identifed by the observers of these shrikes, and as would be expected based on the breeding and winter ranges of parental populations. Both plumage and morphological features also suggest that the Mendocino shrike is better placed with the former group, as an individual from the zone of hybridization between Red-backed and Turkestan Shrikes. Studies of hybrids have shown that, whereas plumage charac - ters can be determined by multiple alleles resulting in various combinations of parental traits and occasionally traits shown by neither parental species, structural traits of recombi - nants more consistently show states interme- diate between those of parentals (Rohwer et al. 1994, Graves 1996). A possible dominance of Red-backed Shrike genes, as displayed by both plumage and morphological characters, might further suggest that the Mendocino shrike was a product of a broadly introgressed zone of overlap and hybridization as found between Red-backed and Turkestan Shrikes but not extensively between Red-backed and Isabelline Shrikes or Red-backed and Brown Shrikes (Panov et al. 2011), although at least one presumed male of the latter hybrid combi - nation has been documented successfully rais- ing young with a female Red-backed Shrike (Kryukov and Gureev 1997; Figure 21). Conclusions We recommend that the Mendocino shrike be considered a product of the Red-backed/ Turkestan Shrike zone of hybridization. As in all identifcations involving hybrids (and many involving pure species), a degree of un - certainty is unavoidable. We believe, however, that the combination of suggestive plumage and perhaps vocal features with more reli - able and indicative wing and tail morpholo- gies, as compared with these criteria in both specimens and other hybrids, indicates this as the most parsimonious conclusion and a rea - sonable one within the realm of identifcation certainties. The Red-backed/Turkestan Shrike hybridization zones from the Caspian Sea to the Altai region of south-central Russia repre - than with products of genetically introgressed populations. The plumage of these seven hy - brids generally resembled that of the Men- docino shrike (Figures 20a-b, 21), but most of them showed a lack of whitish to the supercil - ial region, browner or mixed brown and gray uppertail coverts that did not contrast in color with the back, brown (or brownish-tinged) rather than rufous bases to the outer rectrices, more extensive and deeper buff (rather than apricot) tones to the sides and fanks, and white not extending beyond the primary co - verts. However, at least one of the seven hy- brids showed each of these features analogous to those of the Mendocino shrike, with the ex - ception of rufous at the base of the tail. For ex- ample, the specimen from the Kuznetsk Alatau range showed a whitish supercilium (Figure 21), and an individual photographed in Japan (Figure 20b; Figures 8, 9 in Young Guns 2014) showed white at the bases of the primaries extending beyond the primary coverts. This appears to confrm the risk of plumage assess - ment in hybrids, due to variable combinations of phenotypic expression contributed by each parent, along with occasional contradictory character states, as noted above. The tip of the outer two rectrices (r5 and r6) were visible on six of these seven hybrid shrikes from eastern Asia (e.g., Figures 20c-d, 21), allowing assessment of tail morphology. The proportion of the distance between r5 and r6 to that of the length of r6 in the images (c/d in Figure 15) ranged from 0.137 to 0.230, not overlapping the range in these proportions cal - culated from images of the Mendocino shrike or of the 16 presumed Red-backed x Turke - stan Shrike hybrids noted above, instead be- ing consistent with what might be expected of Red-backed x Brown Shrike hybrids (see Table 1b). The length of the outer rectrix (r6) was shorter relative to the overall tail length in all seven presumed Red-backed x Brown Shrike hybrids than it was in the Mendocino shrike or any of the 14 presumed Red-backed x Turkestan Shrike hybrids in which this could be assessed. Primary morphology could also be as - sessed in photographs of two of the Japanese hybrids, shown in Figure 2 of Horimoto and Watabe (2014) and Figure 9 of Young Guns (2014). Using the methods described above, the distances between p8 and p9 and between p9 and the primary coverts in the images (a/b in Figure 15) resulted in ratios of 0.233 and 0.188, respectively, consistent with what would be expected of a Red-backed x Brown Shrike hybrid but greater than that expected of a Red-backed x Turkestan Shrike hybrid, according to specimen-based data, and greater verts (Figure 18a-b), the latter of which was present in 25 of the 28 (perched) individuals. Notably, these 28 hybrid shrikes show tail structural morphologies that match that of the Mendocino shrike. Among 14 individuals for which the outer rectrix tips were visible, using the methods applied above (Figure 15), the ratio of the tips of r5 to r6 to the estimated length of r6 in the images (c/d in Figure 15) ranged from 0.093 to 0.135 (e.g., Figure 18c- d). This ratio in two specimens identifed as Red-backed x Turkestan Shrike hybrids at the Field Museum of Natural History (FMNH 200775 and 200777; see Figure 19a) was also similar, being 0.103 and 0.102, respectively (J. Engle, pers. comm.). These ratios are similar to those calculated from images of the Mendoci - no shrike and specimens of Red-backed Shrike and overlap with the lower end of the ranges from Turkestan Shrike specimens (Figure 15b- c, Table 1b). Similar variation in these ratios appears evident from a visual examination of the series of Red-backed x Turkestan Shrike hybrids shown in Figure 17.1 of Panov et al. (2011). The tip of p9 was insuffciently visible in images of these 28 hybrid shrikes, preclud - ing a comparison of wing morphologies (see Figure 15a) with that of the Mendocino shrike. However, in three specimens at FMNH identi - fed as Red-backed x Turkestan Shrike hybrids (83458, 200776, and 200777; see Figure 19), the ratio of p9-p8 to p9-primary coverts (a/b in Figure 15, above) was 0.078, 0.099, and 0.191 (J. Engle, pers. comm.), similar to or shorter than estimated ratios calculated from images of the Mendocino shrike. Ratios for both wing (a/b) and tail (c/d) morphologies from these presumed Red-backed x Turkestan Shrike hybrids all fall well below the ranges of these ratios calculated from Brown Shrike specimens (Table 1b). The remaining six hybrids were photo - graphed in Malaysia (Mun 2015; Figure 20a) and Japan (e.g., Horimoto and Watabe 2014, Young Guns 2014; Figure 20b), with most of those in Japan being identifed as Red-backed x Brown Shrike hybrids (Y. Watabe, in litt.; we have excluded the shrike documented by Furuichi et al. 2010, which may well repre - sent a pure Red-backed Shrike). We also ana- lyzed images of the specimen of Red-backed x Brown Shrike hybrid collected in 1983 in the Kuznetsk Alatau range of Russia, where both species were breeding and mixed pairs were observed (Kryukov and Gureev 1997; Figure 21). The plumage of these seven shrikes ap - peared more comparable to each other than those of the 28 presumed Red-backed x Turke - stan Shrike hybrids discussed above, showing characters more consistent with F 1 hybrids

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