Date of Award

January 2011

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)


Biological Sciences

First Advisor

Gary Ritchison

Department Affiliation

Biological Sciences


To maximize reproductive success, parents may, in some cases, differentially invest in sons and daughters, i.e., sex-biased parental investment. Preferential provisioning behavior has been reported in one population of Eastern Bluebirds (Sialia sialis) and attributed to local resource competition. To better understand this behavior, I studied the provisioning behavior of Eastern Bluebirds in Madison County, Kentucky, in 2004. I experimentally manipulated brood sex ratios in 24 bluebird nests, creating female-biased (N = 8), male-biased (N = 5), and control (N = 11) nests. Following manipulation, nests were video-taped to record adult provisioning behavior. Among experimental broods, the provisioning rates of male and female Eastern Bluebirds were not affected by brood sex ratio (P = 0.58). Similarly, for broods that naturally differed in the number of male and female nestlings (N = 9), I found no effect of brood sex ratio on provisioning rates (P = 0.34).

Female bluebirds provisioned nestlings at higher rates than males (P = 0.0046) and the provisioning rates of adult bluebirds varied with brood size (P = 0.017); with broods of 5 fed at lower rates than broods of either 3 or 4. Because surface area exposure per nestling is reduced in larger broods, nestlings in larger broods may expend energy at lower rates and require less food from adults.

Male and female bluebirds delivered a total of 2363 prey items to nestlings, with males delivering 821 prey items and females 1542 prey items. Of prey items I was able to identify, grasshoppers (Orthoptera) were the most common prey delivered to nestlings by both male and female bluebirds. Other common prey items included Lepidopteran larvae, beetles (Coleoptera), crickets (Orthoptera), worms (Oligochaetaspp.), spiders (Araneae), and cicadas (Hemiptera). Overall, male and female bluebirds delivered similar types of prey to nestlings.

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Biology Commons