Date of Award

January 2011

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

Most songbirds are visually sensitive to ultraviolet (UV) wavelengths and, in some species, variation in the extent to which plumage reflects in the UV range provides information about individual quality that influences mate-choice decisions. Less is known about the possible importance of plumage UV reflectance in parent-offspring relationships. The lower breast and belly plumage of nestling Eastern Phoebes (Sayornis phoebe) reflects in the UV and adults may use variation in this reflectance to evaluate nestling quality and vary their provisioning behavior accordingly. To examine this possibility, I manipulated UV reflectance of nestling plumage by applying preen oil that either did or did not contain UV-blocker. After treatment, nestlings were placed in an experimental apparatus with individual chambers for each nestling and the provisioning behavior of adult phoebes was monitored over a two-day period by videorecording. I conducted experiments with 25 broods of Eastern Phoebes at the Blue Grass Army Depot in Madison County, Kentucky, in 2010, including 13 first broods and 12 second broods. Control and UV-blocked nestlings were fed at similar rates (P = 0.72) by male and female Eastern Phoebes, indicating that variation in UV reflectance of nestling lower breast and belly plumage does not influence adult provisioning behavior. The color of the yellow breast and belly feathers of nestling phoebes may be a selection neutral trait that is correlated with adult plumage characteristics that have other signaling functions. I found that first broods were fed at higher rates than second broods during both pre- (P = 0.001) and post-treatment time periods (P < 0.0001). Young in first broods may survive at higher rates than those in second broods. As such, adult phoebes may invest more in those young that are most likely to contribute to their reproductive fitness. However, reduced provisioning rates for second broods may also result from decreased thermoregulatory demands of nestlings hatching later in the summer when ambient temperatures are higher. Finally, female Eastern Phoebes fed nestlings at higher rates than males during post-treatment time periods (P = 0.001). Differences between the sexes may be due to sex-specific differences in the costs and benefits of investing in young or to sex-specific differences in parental roles. For example, male phoebes may spend more time in other activities, such as territory defense, while females spend more time provisioning nestlings.

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