Isolating weather effects from seasonal activity patterns of a temperate North American Colubrid.

Forecasting the effects of climate change on threatened ecosystems and species will require an understanding of how weather influences processes that drive population dynamics. We have evaluated weather effects on activity patterns of western ratsnakes, a widespread predator of birds and small mammals in eastern North America. From 2010-2013 we radio-tracked 53 ratsnakes in the fragmented region of central Missouri. We relocated each snake 4× per week and used movement frequency as an index of activity. We used generalized linear mixed models within an information-theoretic approach to evaluate temporal and weather variables as potential predictors of snake activity. While snakes were generally sedentary, activity showed a linear response to relative humidity and a quadratic response to air temperature, peaking near 30 °C. Seasonal activity patterns differed between sexes and among years, but snakes were generally least active in mid-summer, regardless of weather. Our findings provide strong evidence that air temperature and relative humidity differentially affect activity patterns of an important predator and are the mechanism explaining increased nest predation rates with warmer temperatures.