The Hormonal Control of Territorial Aggression in Tropical Birds

Abstract

Investigations of the hormonal control of avian territorial aggression have focused on temperate zone species where typically only males sing and defend territories in the breeding season, and have implicated testosterone in the control of these behaviors. However, most avian species are tropical and in many such species both sexes sing and defend year-round territories. We have examined the mechanisms underlying territoriality in the White-browed Sparrow Weaver Plocepasser mahali, in Zambia, and the Bay Wren Thryothorus nigricapillus, in Panama. In both species, we found low circulating levels of steroid hormones and no evidence for the regulation of territorial aggression by testosterone even in the breeding season. However, there were preliminary indications of a role for luteinizing hormone in maintaining territorial aggression. Thus, in contrast to temperate zone species, territorial aggression in these two tropical species is either independent of control by steroid hormones or is mediated by a non-gonadal hormone. These results, and the few data from other tropical species, suggest that the general assumption that androgens maintain territorial aggression may apply only to temperate species.