Orientation affects nest temperature of ground-nesting birds

Abstract

Temperature of avian nest sites is a critical component of reproduction because thermal environments influence both fitness and survival of incubating adults and developing embryos. Given that the orientation of nest sites can alleviate or intensify thermal extremes through exposure to solar radiation and wind effects, it is important to quantify the mechanistic role orientation has on thermal conditions. Moreover, identifying how nesting decisions (i.e., orientation) influence nest site temperature may also provide insight into the adaptive responses of species commonly exposed to thermal extremes. Therefore, to better understand the relationship between nest orientation and nest site temperature, we examined nest sites of 2 ground-nesting sympatric species, Northern Bobwhite (Colinus virginianus) and Scaled Quail (Callipepla squamata), in the Southern Great Plains, a region prone to high thermal variability. Specifically, we measured temperature of nest sites by nest orientation using black bulb temperature (Tbb) data loggers. We found that, despite uniform distribution of nest orientations, orientation was a major driver of nest site temperature during peak heating periods (1200–1830 h) with temperatures of south- and west-facing nests on average 6 °C warmer for Northern Bobwhite and 2 °C warmer for Scaled Quail when compared to the temperature of north- and east-oriented nests. However, no significant differences were observed in nest vegetation characteristics between nest orientations, and orientation failed to predict nest success for either species. This is contrary to similar studies and suggests that nest site selection is an interaction between multiple drivers (i.e., thermal environment, predation risks) with the importance of factors varying between years and locations.