Hormone-Behavior Adaptations in Arctic Birds

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Arctic breeding birds arrive on their nesting grounds at a time when weather conditions may still be extreme (low temperature, snow). However, the brief arctic summer requires that they begin nesting as early as possible to take advantage of the ephemeral abundance of food to feed young. Failure to adhere to this rigid schedule results in drastically reduced reproductive success. Hormone-behavior adaptations that maximize survival and reproductive success under the extreme conditions of the Arctic are the focus of this proposal. It has been shown that the interrelationships between testosterone and territorial aggression are diverse, especially as birds arrive on the arctic breeding grounds. In some species territoriality is extremely brief, following which birds apparently become refractory to the effects of testosterone. Others are territorial throughout the breeding season, but the dependence of these behaviors upon testosterone activation remains unclear. Aggressive behavior of between four and seven arctic breeding passerines displaying different types of territoriality will be compared. Temporal patterns of testosterone in relation to patterns of aggressive behavior and the effects of manipulating testosterone level will also be determined. Additionally, these species will be compared with their closest relatives breeding at mid-latitudes (i.e. matched pairwise comparisons to avoid confounding issues relating to phylogenetic relationships). In this way it is possible to determine the ecological bases of different types of territorial behavior and interrelationships with testosterone, as well as indicate potential specializations of arctic breeding birds. The same spectra of species in the Arctic and at mid-latitudes will be used to compare adrenocortical responses to stress. Extensive data now indicate that arctic birds modulate the secretion of corticosterone in response to a standardized capture stress protocol as a function of latitude and stage in the breeding cycle. This is thought to be an adaptation to allow onset of territorial behavior and breeding in the face of potentially stressful conditions. Both arctic and mid-latitude species will be compared. Behavioral and physiological responses to corticosterone treatment will be determined within these species comparisons to indicate how endocrine mechanisms may vary in relation to latitude and other ecological factors. Finally, laboratory experiments will assess the number and distribution of receptors for testosterone (and possible metabolites) and corticosterone in the central nervous system. This unique approach of field experiments to compare types of territorial behavior in arctic and mid-latitude passerines, effects of hormones and stress, and ultimately the related distribution of hormone receptors in the brain will not only pinpoint specific adaptations for birds breeding in the Arctic, but will have significance for the regulation of reproductive processes of vertebrates in general.