Interspecific Mate Choice Following Cross‐fostering in a Mixed Colony of Greylag Geese ( Anser anser ) and Canada Geese ( Branta canadensis ). A Study on Development and Persistence of Species Preferences 1

The role of early experience in mate choice and species preference of geese was studied in an experiment where young greylag geese ( Anser anser ) were cross‐fostered by Canada geese ( Branta canadensis ). In two successive years, all eggs from 9 nests of wild Canada geese were removed and replaced by greylag goose eggs. The young greylag geese then followed their Canada goose foster parents on their southward migration in autumn, to return with them in spring. Of 35 returning birds, all 16 females paired with greylag goose males (100%) whereas of 19 males 5 paired with Canada goose females (14%) and the remaining 14 with greylag goose females (74%). The pair bonds generally persisted as long as both birds were present, but after loss of a partner, the remaining bird usually re‐mated. Even when this happened several times during the lifetime of a male, the new mate was always a Canada goose female, showing that the males were sexually imprinted to this species. The Canada goose females which had mated with the greylag ganders also remated when widowed, but their new mate could be either a Canada goose or a greylag goose.