DHEA levels and social dominance relationships in wintering brent geese (Branta bernicla bernicla)

After testosterone, dehydroepiandrosterone (DHEA) is the main hormone involved in aggressive behaviour in birds. While the role of DHEA has been verified for wintering territorial passerines, it has not been shown for gregarious species. In wintering geese species, both sexes present very low testosterone levels and aggression in a non-sexual context is not testosterone-related. Therefore, testosterone does not seem to be responsible for aggressive behaviour by geese during winter and the role of DHEA must be explored. We used brent geese (Branta bernicla bernicla) to examine the roles of testosterone and DHEA in dominance relationships. For the first time, we highlighted the presence of plasma DHEA in free-living geese. As the level of DHEA was lower than that of testosterone, and there was no obvious impact of DHEA level on dominance status, our results failed to confirm the role of plasma DHEA in the social hierarchies of this species during winter. Nevertheless, because DHEA levels were greater in singletons than in paired birds, we discuss the need to explore hormonal and/or behavioural mechanisms implicated within dominance status acquisition and maintenance within each reproductive status class, to underline the role of the presence of relatives as a signal of dominance abilities. We also acknowledge and discuss the possibility that the long handling time may have affected DHEA levels and masked subtle differences between individuals.