Clinal Size Variation in Canada Geese Affects Morphometric Discrimination Techniques

Abstract

We evaluated morphometric discrimination models designed to use skull length to differentiate between giant Canada geese (Branta canadensis maxima) and interior Canada geese (B. c. interior). We found significant differences in mean skull lengths of interior Canada geese from 3 areas in James Bay (Duncan's multiple range test, P < 0.05). Geese decreased in size with increasing latitude, but those from Akimiski Island did not fit this pattern, and were smaller than those from the adjacent mainland. Morphometric discrimination techniques appeared to work adequately in northwest James Bay and on Akimiski Island, but were less reliable in southern James Bay, where the largest interior Canada geese were found. Molt migrant giant Canada geese were apparent in all areas, but most were distinguishable by morphometric methods from interiors at all sites except southern James Bay. Detailed knowledge of geographic variation in body size will improve the usefulness of morphometric discrimination techniques for Canada goose research and management. We recommend the skull length models developed by Moser and Rolley (1990) for use in differentiating giant from interior Canada geese in much of the Mississippi Flyway, except where southern James Bay mainland geese occur. J. WILDL. MANAGE. 61(1):183-190