Meeting Abstract

109.2  Sunday, Jan. 6  Effects of testosterone on spring nocturnal migratory restlessness and body composition in Zonotrichia albicollis VANDERMEER, C.L.*; BEZNER KERR, W.; GUGLIELMO, C.G.; MACDOUGALL-SHACKLETON, S.A.; Univ. of Western Ontario, London; Univ. of Western Ontario, London; Univ. of Western Ontario, London; Univ. of Western Ontario, London cvande67@uwo.ca

Photoperiod influences a number of hormonal cascades that modulate seasonal changes in behaviour and physiology. In the spring, many bird species migrate to breeding grounds, where androgens and estrogens promote courtship and territory defence behaviours. Testosterone also increases muscle mass and fat deposition rates via hyperphagia, supplying migrating birds with additional fuel. Captive birds exposed to photoperiod cycles display migratory restlessness in the form of nocturnal hopping activity (Zugunruhe). Precise endocrine modulation of this migratory behaviour and physiology is unclear, however castrations decreased the rate of spring Zugunruhe in prior experiments. Our study compared Zugunruhe and body composition in castrated and intact white-throated sparrows (Zonotrichia albicollis) following photoperiod and hormone manipulation. Intact sham-operated males kept on short days (non-migratory) did not exhibit Zugunruhe behaviour, while those switched to long days did. Long-day castrates implanted with androgen blockers (flutamide) and an aromatase inhibitor (ATD) displayed minimal nocturnal activity intermediate to that of short-day and long-day intact males. Long-day castrates given testosterone replacement exhibited higher levels of nocturnal activity than the three other groups. Flight muscle, heart and liver mass differed among the four treatment groups, generally showing greater size in the testosterone replacement group. Our results indicate that long day exposure in spring will elicit Zugunruhe, but that testosterone enhances photoperiod-induced migratory restlessness and organ changes.