Date of Award

January 2013

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Gary Ritchison

Department Affiliation

Biological Sciences

Abstract

Nestling birds solicit food from their parents using conspicuous vocalizations and visual begging displays and there is considerable empirical evidence suggesting that nestling begging represents honest signals of need, and that adults use these signals to determine provisioning rates. Less is known about how males and females may differ in their response to changes in nestling begging behavior as a result of variation in hunger levels, or how nestling begging and adult provisioning may be influenced by brood number (i.e., first versus second broods).

To examine these parent-offspring interactions, I first manipulated hunger levels of whole broods of nestling Eastern Phoebes (Sayornis phoebe) during the 2011 breeding season at the Blue Grass Army Depot in Madison Co., KY, to determine if nestling begging was positively correlated with hunger. Both first and second broods were divided into three treatments: (1) hand-feeding to satiation all nestlings in a brood (fed treatment, N = 12), (2) depriving all nestlings of food (deprived treatment, N = 16), and (3) feeding some nestlings in a brood and depriving the others (some deprived/some fed treatment, N = 14). Nestling begging and adult provisioning behavior was videotaped both before and after treatments were administered to analyze responses to experimental manipulation of nestling hunger level.

Nestling begging behavior varied significantly among treatments, but there was no significant interaction between brood and treatment, and the begging behavior of nestling phoebes was not affected by the sex of the visiting adult. When broods were food-deprived, nestling begging intensity increased. Conversely, when whole broods were fed, both begging intensity and proportion of nestlings begging decreased. For some deprived/some fed broods, the change in begging intensity after treatment was between that of fed and deprived broods. Adult Eastern Phoebes adjusted their provisioning rates in response to changes in the begging intensity of nestlings, provisioning food-deprived nestlings at higher rates and nestlings in fed and some fed/some deprived broods at lower rates. These results suggest that nestling begging is an honest signal of need and that parents respond to variation in nestling begging by adjusting their provisioning behavior, consistent with predictions of signaling models.

Although the overall provisioning rates of male and female phoebes did not differ, post-treatment responses of adults to changes in the begging behavior of nestlings differed for first and second broods. For both first and second broods, adult phoebes reduced provisioning rates to nestlings in fed and some fed/some deprived 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 by adult phoebes may be a result of environmental factors, including weather and prey availability, or may represent a trade-off between investment in current and future reproduction.

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