Many factors, including nestling age, brood size, and mate quality, can influence the provisioning behaviour of adult birds. Mate quality may affect provisioning behaviour because high-quality individuals may be ‘good parents’ and provision at higher rates. Alternatively, individuals paired to high-quality mates may provision at higher rates because the benefits provided by such mates ( e.g. good genes) increase the likelihood of reproductive success. We examined variation in the plumage colour of male and female Eastern Phoebes ( Sayornis phoebe) and the possible relationship between such variation and provisioning behaviour. During the 2006–2007 breeding seasons, we captured, banded, and measured adult Eastern Phoebes and collected belly feathers for spectral analyses. We also videotaped nests to quantify provisioning behaviour. Male Eastern Phoebes were larger than females, but the plumage (belly feathers) of males and females did not differ in brightness, hue, and carotenoid chroma (all P ≥ 0.37). Females provisioned nestlings at higher rates than males ( P = 0.009), but we found no significant relationship between provisioning rates of males and females and plumage colour. However, relationships between female provisioning rates and the brightness and carotenoid chroma of their mates’ belly feathers approached significance ( P ≤ 0.08). The larger size of male Eastern Phoebes suggests there is male–male competition for access to resources ( e.g. nest sites and mates), with larger size conferring a selective advantage. However, the absence of intersexual differences in plumage colour suggests limited sexual selection driven by female choice for extra-pair partners. Differences in provisioning rates of males and females may be due to male uncertainty of paternity status or to intersexual differences in foraging behaviour. The relationship between female provisioning rates and male plumage quality suggests that females may invest more in reproduction if male Eastern Phoebes with brighter, carotenoid-rich belly plumage are better able to provide quality nest sites and territories or, perhaps, high-quality genes that can potentially enhance female fitness (differential-allocation hypothesis).
Coevolution of male and female mate choice can destabilize reproductive isolation