LANDYS, M.M.*; GOYMANN, W.; SOMA, K.K.; SLAGSVOLD, T.; Univ. of Oslo, Norway; Max Planck Institute of Ornithology, Andechs; Univ. of British Columbia, Vancouver; Univ. of Oslo, Norway: Dehydroepiandrosterone (DHEA) and territorial aggression in the European nuthatch

During breeding, territorial aggression in male birds is closely linked to secretion of gonadal testosterone (T). However, hormonal regulation of territoriality outside of the context of reproduction, when T circulates at basal levels, is not as clear. Recent studies propose that the steroid dehydroepiandrosterone (DHEA) may support territoriality during non-breeding. DHEA can be synthesized by the adrenals and converted to androgens and estrogens in the avian brain. We examined the role of DHEA in the regulation of non-breeding aggression in the European nuthatch (Sitta europaea). This species defends food caches throughout the year and shows aggressive responses to conspecifics during both the breeding and non-breeding periods. Because female nuthatches are as aggressive as males, this species serves as an excellent model to also investigate the hormonal correlates of female aggression. Our field studies demonstrate that plasma DHEA is detectable during breeding and non-breeding in both sexes, while plasma T is detectable only in breeding males. We also experimentally treated free-living male birds with DHEA during autumn and examined aggressive responses to simulated territorial intrusion. DHEA-treated birds showed increased aggression in comparison to controls. Our results support previous findings and suggest that plasma DHEA may serve as an important alternative to T in the regulation of territorial behavior, especially because circulating T also stimulates costly physiological and morphological changes. Minimizing costs associated with territoriality may be especially important in the examined population of nuthatches given the harsh winter conditions in Oslo, Norway (avg. temp. of -4� C, snow cover ≥20 days/month).