EFFECTS OF VARIATION IN NESTLING HUNGER LEVELS AND BEGGING ON THE PROVISIONING BEHAVIOR OF MALE AND FEMALE EASTERN PHOEBES (SAYORNIS PHOEBE)

Nestling birds solicit food from their parents using conspicuous vocalizations and visual begging displays, and evidence suggests begging represents an honest signal of need that adults use to determine provisioning rates. Less is known about how adult males and females may differ in response to changes in nestling begging behavior as a result of variation in hunger levels or how nestling begging and adult provisioning may vary seasonally in multi-brooded species. To examine these parent-offspring interactions, we manipulated hunger levels of nestling Eastern Phoebes (Sayornis phoebe) during the 2011 breeding season in central Kentucky. Both first and second broods were divided into three treatments: whole brood fed (n = 12), whole brood deprived (n = 16), and some fed/some deprived (split; n = 14). Food-deprived nestlings begged with increased intensity, and fed broods begged with less intensity. Adult Eastern Phoebes adjusted their provisioning rates accordingly, provisioning food-deprived nestlings at higher rates than fed and split broods. These results suggest that nestling begging is an honest signal of hunger and parents respond to variation in nestling begging by adjusting their provisioning behavior. Provisioning rates of male and female phoebes did not differ, but post-treatment responses of adults differed for first and second broods. For both first and second broods, adults reduced provisioning rates to nestlings in fed and split broods. However, food-deprived nestlings in first broods were fed at similar rates before and after treatment, whereas food-deprived nestlings in second broods were provisioned at much higher rates after treatment. Differences in the provisioning of first and second broods may represent a trade-off between investment in current and future reproduction.