The Evening Grosbeak (Coccothraustes vespertinus) is a nomadic species that ranges across North America. This species has been in decline in recent years, and the taxonomic status of its subspecies is uncertain. Five distinct variants, or types, in flight calls produced by individuals in different geographic areas have been observed. What variations occur in other vocalizations, and whether this species uses various vocalizations to identify other members of the species, has not been studied. Here I quantify variation in 240 flight calls of 24 individuals representing three western types (Type 1, Type 2, and Type 4), and 75 trill calls of 5 individuals of one of the types. I examine sex-based differences in flight calls, and compare the morphologies of these three populations to determine if any differences exist. Coefficients of variation (CV) and ANOVAs show that the flight calls vary more between types than among individuals within types. Trill calls vary both among individuals and types. These levels of variation suggest that the flight call and trill call can convey different levels of identification (population or taxon versus individual). No sex-based differences in the fight calls were detected. No significant morphological differences among birds that produce different flight call types were found in body size. Significant differences were found in female bill morphology and a nearly significant trend was found in one male bill morphology measurement. Variations in vocalizations that allow identification at different levels could have significant influence on flock assemblage and mate selection, and so contribute to speciation in nomadic species. Differences in bill morphology could indicate specialization in feeding behavior.
|Advisor:||Coombs-Hahn, Thomas P.|
|Commitee:||Eadie, John, Patricelli, Gail|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||MAI 50/03M, Masters Abstracts International|
|Subjects:||Zoology, Behavioral Sciences|
|Keywords:||Evening grosbeak, Morphological variation, Nomadic species, Subspecies, Vocal variation|
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