Genetically-based behavioural morph affects stopover refuelling performance in white-throated sparrows Zonotrichia albicollis
J. Morgan Brown, Brendan J. McCabe, Lisa V. Kennedy, Christopher G. Guglielmo
Intraspecific competition can influence refuelling at migration stopover sites. White-throated sparrows Zonotrichia albicollis have genetically-determined plumage morphs that differ in dominance behaviour and competitive abilities. This study examines the effects 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 profiling to determine body composition and refuelling rates, respectively. We determined sex and plumage morph genetically. Competitive ability did not influence migration timing. Controlling for structural size, males had larger lean mass than females, but we found no differences 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 differences 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 offset gains from faster refuelling rates.