干旱区生态环境知识资源中心

Geographic variation in external morphology of one subspecies of Red-tailed Hawk (Buteo jamaicensis calurus) in western North America was analyzed by comparing measurements of 249 museum specimens from seven ecoregions. Male and female Red-tailed Hawks showed substantial regional variation within the geographic range of this single subspecies. We used exploratory and confirmatory data analysis to investigate relationships between morphological and environmental variables. Canonical correlation indicated associations between morphology and continuous environmental variables. Five of six morphological measurements varied concordantly and were taken, collectively, to indicate size. In general, largest hawks occurred in the arid southwestern deserts and California grasslands, and smallest in the cool, humid Pacific Northwest. Tarsus length showed a pattern of variation opposite from other measurements, with longest tarsi in the Pacific Northwest. The traditional ecogeographic rules of Bergmann and Allen were not supported. nor did size appear to be related to availability of food. Our results were found to be consistent with some other ecomorphological hypotheses, such as James’ "Neo-Bergmannian" hypothesis and those involving niche breadth, prey size and water conservation. Studies of the development, quantitative genetics and functional significance of size and shape are needed to understand the causes of ecogeographic variation.