Year-round territorial aggression is independent of plasma DHEA in the European nuthatch Sitta europaea

► We examine the seasonal DHEA profile in a year-round territorial songbird. ► We test effects of DHEA treatment on non-breeding territoriality in autumn. ► Plasma DHEA shows no seasonal variation and is often undetectable. ► DHEA treatment does not enhance non-breeding aggression or its persistence. ► We report that DHEA does not relate to non-breeding territoriality in this species.