HORMONES AND TERRITORIAL BEHAVIOR DURING BREEDING IN SNOW BUNTINGS (PLECTROPHENAX-NIVALIS) - AN ARCTIC-BREEDING SONGBIRD

We examined hormonal profiles and behavior associated with maintaining a single-purpose territory in an Arctic-breeding songbird - the snow bunting (Plectrophenax nivalis). Snow buntings differ from many other Arctic-breeding passerines by using nest cavities, an uncommon and def ended resource, but not relying upon the surrounding territory for for age. Circulating levels of testosterone in males were high when territ ories were established and then decreased over the breeding season. LH secretion was enhanced in females while laying eggs, followed by dete ctable levels of estradiol during incubation. Both sexes showed equiva lent corticosterone responses to the stress of being captured and held . Male snow buntings vigorously defended territories in response to a simulated territorial intrusion both when initiating breeding and when feeding young. Exogenous testosterone implants surprisingly inhibited physical aggression but enhanced singing when birds were feeding youn g, thus suggesting that song and physical aggression are mediated by d ifferent hormonal mechanisms at this time of year. Together, these res ults contrast with hormonal profiles and behavior in other Arctic-bree ding passerines. (C) 1998 Academic Press.