title: Testosterone, migration distance, and migratory timing in song sparrows Melospiza melodia.
abstract: 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 at the time of arrival to the breeding site and its relationship to overwintering latitude in male and female song sparrows (Melospiza melodia). We used stable isotope analysis of hydrogen (δ(2)H) in winter-grown claw tissue to infer relative overwintering latitude (migration distance), combined with 14years 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 breeding 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 indicate that androgens and migration distance are correlated traits within and between sexes that may reflect individual variation within an integrated phenotype in which testosterone has correlated effects on behavioral traits such as migration.
authors.affiliation: Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5B7, Canada.
authors.forename: Alannah H
authors.initials: AH
authors.lastname: Lymburner
authors.affiliation: Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5B7, Canada.
authors.forename: Tosha R
authors.initials: TR
authors.lastname: Kelly
authors.affiliation: Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5B7, Canada.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hobson
authors.affiliation: Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5B7, Canada.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: MacDougall-Shackleton
authors.affiliation: Advanced Facility for Avian Research, Department of Biology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5B7, Canada; Advanced Facility for Avian Research, Department of Psychology, University of Western Ontario, 1151 Richmond Avenue, London, ON N6A 5C2, Canada. Electronic address: smacdou2@uwo.ca.
authors.forename: Scott A
authors.initials: SA
authors.lastname: MacDougall-Shackleton
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D005260:Female; D006702:Homing Behavior / Q000502:physiology*; D008297:Male; D010641:Phenotype; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D012727:Sex Characteristics; D046370:Sparrows / Q000097:blood / Q000502:physiology*; D013739:Testosterone / Q000097:blood*; D013997:Time Factors
chemical_list: D013739:Testosterone
keywords: Androgens; Deuterium; Differential migration; Isotope ecology; Migration; Protandry; Testosterone