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Abstract

Given the critical role of temperature in avian reproduction, rising global temperatures will likely impact reproductive success of many bird populations. We examined the effect of nest box temperature, nest box color, entrance orientation, distance to forest cover, and distance to water on net box selection, nest success, and nestling size in eastern bluebirds (Sialia sialis) in central Georgia. White painted nest boxes had significantly cooler temperatures than control nest boxes (P < 0.05). However, model selection revealed that eastern bluebird females selected control boxes, despite their overall warmer temperatures. Nest success was associated with year, likely because of high nest predation during the warmer 2022 breeding season (P < 0.05). Nest success was also associated with cooler nest boxes, possibly because incubating females spend more time incubating which can reduce predation risks. Larger nestlings fledged from painted nest boxes, nest boxes with cooler temperatures, and nests from 2021, which we attribute to decreased thermoregulatory demands enabling faster nestling growth in cooler boxes and years. These seemingly opposing results suggest there may be an optimal temperature range where nest box temperature maximizes reproductive fitness while minimizing energetic demands on incubating adults. Determining this temperature range can help target management efforts to ensure specific goals are met.

Acknowledgements

We thank Charlie Muise and Mathew Gordon for assisting with field research, and the Panola Mountain Bluebird Network for granting access to their nest boxes. We thank Georgia State Parks who allowed access to their property. Thank you to D. DeSantis and M. Milnes for helpful comments on earlier drafts. Georgia College & State University provided materials and support.

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