Comparative morphology among northern populations of breeding Cooper's Hawks

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Few studies at a broad geographical scale have characterized intraspecific variation in morphology of woodland hawks in the genus Accipiter. From 1999 to 2007 we investigated morphological variation in large samples of live Cooper's Hawks (A. cooperii) nesting in four study areas: coniferous woodland around Victoria, British Columbia, Canada, isolated deciduous woodlands in short-grass prairies of northwestern North Dakota, towns and rural deciduous woodlands along the border of North Dakota and Minnesota, and urban and rural mixed deciduous and coniferous landscapes of Wisconsin. These sites span 2660 km across the northern part of the species' breeding range. We measured body mass (i.e., size), wing chord, tail length, tarsus diameter, hallux length, and culmen length of breeding adults, finding significant and clinal variation in body mass (or size). The smallest and most similar-sized birds occurred in British Columbia and western North Dakota, larger birds along the border between North Dakota and Minnesota, and the largest birds in Wisconsin. Several other characters varied significantly when mass was used as a covariate. Variation by study site in mean indices of sexual size dimorphism was negligible and not significant. We speculate that the morphological differences we found, in part, are the result of geographic isolation, where diets, migratory behavior, and structural characteristics of nesting habitats vary across landscape types.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Comparative morphology among northern populations of breeding Cooper's Hawks
Series title Condor
DOI 10.1525/cond.2010.090148
Volume 112
Issue 2
Year Published 2010
Language English
Publisher Cooper Ornithological Society
Contributing office(s) Coop Res Unit Leetown
Description 9 p.
First page 347
Last page 355
Country Canada, United States
State British Columbia, Minnesota, North Dakota, Wisconsin
City Fargo, Grand Forks, Milwaukee, Stevens Point, Victoria
Online Only (Y/N) N
Additional Online Files (Y/N) N
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