Date of Award

January 2020

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

Second Advisor

David R. Brown

Department Affiliation

Biological Sciences

Third Advisor

Luke E. Dodd

Department Affiliation

Biological Sciences

Abstract

To maximize reproductive output, several species of songbirds attempt to raise two or more broods in a single breeding season. The results of previous studies have revealed much variation among species in the factors that influence the likelihood of female songbirds attempting to raise multiple broods during a breeding season. As such, additional studies are needed to better understand the roles of early breeding, brood sizes, and, especially, male parental care in determining the likelihood of having multiple broods. My objective, therefore, was to examine the possible effects of breeding initiation date, brood size, and male provisioning behavior on the number of nesting attempts by female Eastern Bluebirds (Sialia sialis) during a single breeding season. My study was conducted at the Blue Grass Army Depot in Madison County, Kentucky, from mid-March to mid-August 2018. I monitored the nests of 39 first broods, 34 second broods, and eight third broods during my study. Bluebirds were captured in mist-nets and banded with unique combinations of color bands. Adult provisioning behavior was monitored with video-recorders placed from 1.5 – 3 m from nest boxes, and each nest was recorded at least every other day until nestlings fledged. Recordings were subsequently reviewed to quantify the provisioning behavior of male and female Eastern Bluebirds. The combined provisioning rates of male and female Eastern Bluebirds were similar for first, second, and third broods. For first and second broods, males provisioned young at higher rates than females during the first 5-6 days post-hatching, likely because females brooded nestlings during this period. Males did not provision young at higher rates than females during the first 5-6 days post-hatching for third broods, possibly reducing their investment in young in broods late in the breeding season. For broods one and two, the combined provisioning rates of males and females were lower during the first four days post-hatching than for older nestlings, likely because the lower energy requirements of young during the first few days post-hatching. The number of young in broods did not affect the provisioning rates of male and female Eastern Bluebirds (in terms of feeding visits per nestling), with nestlings fed at similar rates regardless of the number of nestlings in a brood. One possible explanation for such results is that young in larger broods have, collectively, less exposed surface area, are better able to thermoregulate, and, therefore, require less food. I found that differences in initiation dates (laying of the first egg), clutch sizes, and brood sizes of first broods did not influence the likelihood of pairs having second and third broods during the breeding season. Rather, differences in individual quality among male and female Eastern Bluebirds may explain differences among pairs in the number of broods they attempt to raise in a breeding season.

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