Effect of Nest Box Temperature Mitigation Treatments on Nest Success and Nestling Condition in a Southeastern Population of Eastern Bluebirds (Sialia sialis)

Understanding behavioral responses of wildlife to climate change will be important as global temperatures continue to rise. Effects of rising temperatures may impact many species, including those that breed in seemingly protected nests, such as cavity nesting birds. Variations in nest cavity microclimate during the early development of secondary cavity nesting passerines may affect the growth of offspring and impact nesting success and survival. We examined the effect of two heat mitigation treatments (white exterior, n=11, and an internal foil heat shield, n=16) and nest box opening orientation (north, south, east, west) on internal nest box temperatures and the effect of internal nest box temperature on nest success and nestling development in a population of Eastern Bluebirds (Sialia sialis) at a restored grassland in central Georgia. We predicted that nest boxes receiving a heat treatment would experience cooler internal temperatures and fledge more offspring of higher body condition compared to control next boxes (n=23). Nest boxes were checked approximately every 3 to 4 days between April and mid-August 2020 and 2021 to record nesting activity and nestling measurements (tarsus and weight). Internal nest box temperature was recorded hourly between April 1st and June 28th using remote data loggers installed on the inside wall of each box. We calculated the maximum daily, minimum nightly and overall averages per nesting attempt and examined the relations of each variable with nestling weight and tarsus length to test the effect of temperature on nest success. White paint applied to the exterior of nest boxes was effective in producing cooler thermal environments compared to control and foil boxes. However, both painted nest boxes and boxes that experienced cooler nightly low temperatures were less likely to be successful. This study highlight the importance of investigating species-specific responses to increasing temperatures before implementing wide-scale habitat modifications