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Geographic Variation in Leach's Storm-Petrel

David G. Ainley
The Auk
Vol. 97, No. 4 (Oct., 1980), pp. 837-853
Stable URL: http://www.jstor.org/stable/4085756
Page Count: 17
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Geographic Variation in Leach's Storm-Petrel
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Abstract

A total of 678 specimens of Leach's Storm-Petrels (Oceanodroma leucorhoa) from known nesting localities was examined, and 514 were measured. Rump color, classified on a scale of 1-11 by comparison with a series of reference specimens, varied geographically but was found to be a poor character on which to base taxonomic definitions. Significant differences in five size characters indicated that the presently accepted, but rather confusing, taxonomy should be altered: (1) O. l. beali, O. l. willetti, and O. l. chapmani should be merged into O. l. leucorhoa; (2) O. l. socorroensis should refer only to the summer breeding population on Guadalupe Island; and (3) the winter breeding Guadalupe population should be recognized as a "new" subspecies, based on physiological, morphological, and vocal characters, with the proposed name O. l. cheimomnestes. The clinal and continuous size variation in this species is related to oceanographic climate, length of migration, mobility during the nesting season, and distances between nesting islands. Why oceanitids frequenting nearshore waters during nesting are darker rumped than those offshore remains an unanswered question, as does the more basic question of why rump color varies geographically in this species.

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