Genetically-based behavioural morph affects stopover refuelling performance in white-throated sparrowsZonotrichia albicollis

Abstract

Intraspecifi c competition can infl uence refuelling at migration stopover sites. White-throated sparrows Zonotrichia albicollis have genetically-determined plumage morphs that diff er in dominance behaviour and competitive abilities. Th is study examines the eff ects of plumage morph, sex and age, three likely indicators of competitive ability, on fall migration timing, body composition, and refuelling rates during stopover at Long Point, Ontario. We used quantitative magnetic resonance analysis and plasma metabolite profi ling to determine body composition and refuelling rates, respectively. We determined sex and plumage morph genetically. Competitive ability did not infl uence migration timing. Controlling for structural size, males had larger lean mass than females, but we found no diff erences in body fat or lean mass between plumage morphs. Plasma metabolite concentrations indicated that the aggressive white-stripe morph refuelled faster than the less aggressive tan-stripe morph, though there were no diff erences among sex and age groups. We suggest that increased refuelling rates did not result in increased fat or lean mass because 1) individuals categorised as less competitive had longer stopover durations to compensate for slower refuelling rates; or 2) costs of behaving more competitively off set gains from faster refuelling rates.