The Influence of Temperature on Black-Capped Vireo Nest-site Selection

Authors: Ronnisha S. Holden, Michael L. Morrison, Heather A. Mathewson

Reproductive success is highly influenced by nest-site selection for avian species in breeding habitats, and variation in the physical environment can drive small-scale changes in the nest-site selection process. We examined the influence of temperature on Vireo atricapilla (Black-capped Vireo; hereafter Vireo) nest-site selection at Kerr Wildlife Management Area (KWMA) in Kerr County, TX (March–July 2013 and 2014). We measured ambient temperature across points that represented the continuum of vegetation characteristics used by Vireos at our study sites during the breeding season. We also found and monitored 181 Vireo nests, collected vegetation data, and compared vegetation characteristics between areas used and not used by Vireos. Finally, we investigated whether Vireo nest-site characteristics changed over the course of the breeding season in relation to the temperature profile of vegetation at our study sites. As expected, temperature increased over the course of the breeding season. Vireo nest sites had higher percent shrub cover than areas not used for nesting by Vireos. Vireos selected different vegetation characteristics for nesting as the breeding season progressed, but we did not find differences in temperature across vegetation types, suggesting that temperature is not the driving factor in Vireo nest-site selection in locations where temperatures remain consistently high throughout the breeding season. However, we could not directly measure temperature at nest-site locations. Therefore, Vireos may exhibit some degree of thermal preference at smaller spatial scales. Additionally, our results suggest that Vireos may require nesting habitat with more shrub cover than previously recommended.