Spatial and Temporal Variation in Feather Corticosterone in House Sparrows (Passer domesticus) and Eurasian Tree Sparrows (Passer montanus)

Abstract

We currently lack knowledge of how the hormone corticosterone (CORT) varies across broad spatial and temporal scales. In birds, CORT acts to make energy available for routine tasks and is also secreted in response to stressors. Evaluating CORT physiology is a powerful tool for determining how individuals are coping with their environment. While CORT has traditionally been measured instantaneously, from plasma, a novel technique for measuring CORT deposited into feathers during growth (CORTf) provides a more holistic, integrated measure of hormone secretion over days to weeks. In addition to exploring how CORT varies in space and time, the present study shows that CORTf is associated with weather variables, corroborating previous findings obtained using plasma CORT. House sparrow (Passer domesticus) CORTf was high in individuals sampled in the hot, dry, north-central region of Mexico. In this population, CORTf was also negatively related to measures of temperature and precipitation. Weather conditions outside of the moult period were stronger predictors of CORTf than conditions experienced during feather growth, indicating that past energetic challenges may have lasting effects on CORT physiology. Over 27 years, variation in CORTf of Eurasian tree sparrows (Passer montanus) in Illinois was not linear, and showed a notable increase in the early 1980s. Tree sparrow CORTf was consistently negatively related to temperature. However, as CORTf was positively associated with spring precipitation and negatively associated with late summer precipitation, temperature-precipitation interactions appear to influence overall energetic requirements. This is the first macrophysiological study using CORTf and these results provide valuable data that can be used as a reference point in future CORTf studies. These findings bring us closer to understanding what habitat conditions are energetically challenging and conversely what conditions are ideal for bird populations. This information is critical for identifying causes of population declines and developing effective conservation measures. The ability to retrospectively analyze CORT using feathers is a highly innovative approach, and by understanding past responses to variation we can more accurately predict how future environmental change will impact populations.