These are gregarious birds, but less social than other "Aythya" species but where common it can form large flocks in winter, often mixed with other diving ducks, such as tufted ducks and common pochards. Forms pairs from January onwards and during courtship the male often curls his tail so that it dips into the water forming a triangular white patch of the undertail coverts. In areas where it is common it will form colonies at protected sites such as islands, often in association with gulls. Where scarce it nests singly, in dispersed and concealed sites.