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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Identification and sex determination of Bicknell's Thrushes using morphometric data
Auteurs :	Sarah J. K. Frey, Auteur ; Christopher C. Rimmer, Auteur ; Kent P. McFarland, Auteur ; Stephane Menu, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (79(4) DEC 2008)
Article en page(s) :	408-420
Langues:	Anglais
Résumé :	The similar plumage of Bicknell's (Catharus bicknelli) and Gray-cheeked (C. minimus) Thrushes have hindered attempts to better understand the nonbreeding biology of these species. We used morphometric data, specifically primary formulae, from Bicknell's Thrushes of known sex and age throughout their breeding range in the United States and Canada to examine possible differences between sex and age classes. We compared these data with similar data from Gray-cheeked Thrushes in Alaska, United States and Newfoundland, Canada to examine mensural characters for distinguishing the two species. We performed a discriminant function analysis (DFA) for each age class to examine morphometric differences between male and female Bicknell's Thrushes. For second-year (SY) and after-second-year (ASY) birds, wing chord was the strongest differentiator, in conjunction with tarsus length. Wing chord and tail length were used to create a discriminant function to differentiate between the two Catharus species. The discriminant functions for both age classes did not permit unambiguous separation of male and female Bicknell's Thrushes nor did the DFA enable unequivocal species identity, but most individuals were correctly classified. Significant differences in the p8-p1 measurement of Bicknell's and Gray-cheeked Thrushes and of male and female Bicknell's Thrushes suggest that this character may be useful to augment published wing chord criteria for species identification and sex determination. Our results indicate that wing chord, in combination with tail length, is the most useful measurement for distinguishing Bicknell's from Gray-cheeked Thrushes and, when augmented with tarsus length, to differentiate between male and female Bicknell's Thrushes outside the breeding season.

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