Meeting Abstract

15-3  Monday, Jan. 4 10:30  Testosterone as a potential mediator of migration distance and migratory timing in song sparrows Melospiza melodia KELLY, T. R. *; LYMBURNER, A. H.; MACDOUGALL-SHACKLETON, E. A.; MACDOUGALL-SHACKLETON , S. A.; The University of Western Ontario; The University of Western Ontario; The University of Western Ontario; The University of Western Ontario tkelly43@uwo.ca http://tosharkelly.wix.com/toshakelly

In seasonally migratory animals, migration distance often varies substantially within populations, such that individuals breeding at the same site may overwinter different distances from the breeding grounds. Shorter migration may allow earlier return to the breeding grounds, which may be particularly advantageous to males competing to acquire a breeding territory. However, little is known about potential mechanisms that may mediate migration distance. We investigated naturally-occurring variation in androgen levels and its relationship to migration distance in male and female song sparrows (Melospiza melodia). We used stable isotope analysis of hydrogen in winter-grown claw tissue to infer relative overwintering latitude (migration distance), combined with 14 years of capture records from a long-term study population to infer the arrival timing of males versus females. Relative to females, males had higher circulating androgen levels, migrated shorter distances, and were more likely to be caught early in the season. Males that migrate short distances may benefit from early arrival at the breeding grounds, allowing them to establish a breeding territory. Even after controlling for sex and date, androgen levels were highest in individuals that migrated shorter distances. Our findings suggest that androgens such as testosterone may mediate variation in migration distance within and between sexes. If so, selection on androgen levels may therefore have correlated effects on optimal migration strategies.