Date of Award

Fall 11-30-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Science

First Advisor

Dr. Katie Stumpf

Second Advisor

Dr. Milnes

Third Advisor

Dr. DeSantis

Abstract

Given the critical role that temperature plays in avian reproductive biology, rising temperatures as a result of global climate change will likely impact reproductive success of many bird populations. Secondary cavity nesting birds, many of which rely on artificial nest boxes to maintain population levels, may be particularly at risk because increased temperatures inside nest boxes can determine whether nest boxes are selected, reduce nest success, and/or negatively affect the growth and survival of offspring. We examined the effect of nest box color on nest box temperature and the influence of nest box temperature, nest box color, entrance orientation, and nest site features (distance to forest cover, distance to water) on nest box occupancy, nest success, and nestling size at fledge in Eastern Bluebirds at a restored grassland in central Georgia. From March-August 2020-2022, we monitored temperature inside 50 nest boxes, recorded nest outcome, and measured nestling size (tarsus). We compared the effect of nest box color on nest box temperatures using an ANOVA and used Akaike’s Information Criterion (AICc) to determine which variables were most strongly associated with nest box occupancy, nest success, and nestling size at fledge. White painted nest boxes had significantly cooler average daily high, average daily lows, and average daily temperatures than control nest boxes. However, Eastern Bluebird females selected boxes with warmer daily lows, daily highs, and daily averages. We posit that this allowed the female to reduce energy expenditure during incubation and shorten the nesting period. Nest success was strongly associated with year, likely because of increased nest predation driven by the warmer ambient temperatures experienced during the 2022 breeding season. Unlike occupancy, cooler nest boxes were associated with increased nest success, possibly due to cooler boxes decreasing trips off the nest by incubating female and thus reducing predation risks. Nestlings that fledged from painted nest boxes, nest boxes with cooler average daily high temperatures, and nests initiated during 2021 were larger. This is likely due to a tradeoff whereby nestlings that don’t have to devote energy to cooling down their bodies can instead devote that energy to growth. These results suggest there may be an optimal temperature range where nest box temperature maximizes reproductive fitness. Determining the optimal temperature range for occupancy, success, and nestling growth may yield conflicting results, but can help target management to ensure specific goals are met.

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