CLINAL SIZE VARIATION IN CANADA GEESE AFFECTS MORPHOMETRIC DISCRIMINATION TECHNIQUES

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 significa nt differences in mean skull lengths of interior Canada geese from 3 a reas in James Bay (Duncan's multiple range test, P < 0.05). Geese decr eased in size with increasing latitude, but those from Akimiski Island did not Bt this pattern, and were smaller than those from the adjacen t mainland. Morphometric discrimination techniques appeared to work ad equately in northwest James Bay and on Akimiski Island, but were less reliable in southern James Bay, where the largest interior Canada gees e were found. Molt migrant giant Canada geese were apparent in all are as, but most were distinguishable by morphometric methods from interio rs at all sites except southern James Bay. Detailed knowledge of geogr aphic variation in body size will improve the usefulness of morphometr ic discrimination techniques for Canada goose research and management. We recommend the skull length models developed by Moser and Rolley (1 990) for use in differentiating giant from interior Canada geese in mu ch of the Mississippi Flyway, except where southern James Bay mainland geese occur.