Too Cold, Too Wet, Too Bright, or Just Right? Environmental Predictors of Snake Movement and Activity
Movement and activity patterns are fundamental to the basic ecology of any organism and can be influenced by a variety of environmental factors. For snakes, which are notable for being secretive and difficult to study, environmental influences on movement are often obscure. Here, we investigate environmental drivers of terrestrial activity for 23 snake species from a temperate community in the Atlantic Coastal Plain region of South Carolina, USA. Activity was strongly seasonal, with primarily fossorial species showing unimodal activity peaks in summer, whereas several aquatic species showed increased terrestrial movements to and from a wetland in both spring and fall. After controlling for seasonal activity, temperature and precipitation had consistent effects on snake movement, with activity of snakes increasing with temperature and decreasing with precipitation. The influence of moon illumination was more ambiguous but may have a weak, negative effect on snake activity. These environmental factors likely drive snake movements because of physiological constraints and trade-offs between foraging success and predation risk. Our results contribute to general knowledge of snake natural history and ecology and may help improve sampling of these elusive organisms that are increasingly in need of conservation attention.
Snake captures vs. day of year from two snake sampling efforts. Each point represents the observed snake count for a given species, and data from all sampling years are plotted. The Land-use Effects on Amphibian Populations (LEAP) dataset (A) represents captures of six primarily terrestrial, small-bodied snakes (2,069 unique sampling date/sampling location combinations). The Ellenton Bay dataset (B) comprises observations of a suite of 20 snake species that differ significantly in their body size, habitat use, and foraging ecology (363 unique sampling dates).
Dotplot showing parameter estimates from the LEAP data global model. Parameter means (circles) and 95% highest posterior density intervals (solid black lines) are shown. The model intercept is excluded from this plot to ease visual interpretation of other parameters. Detailed description of the model structure, environmental predictor variables, and model fitting is given in the main text.
Dotplot showing parameter estimates from the Ellenton Bay data global model. Parameter means (circles) and 95% highest posterior density intervals (solid black lines) are shown. The model intercept is excluded from this plot to ease visual interpretation of other parameters. Detailed description of the model structure, environmental predictor variables, and model fitting is given in the main text.
Dotplot showing species-specific precipitation coefficient parameter estimates from the Ellenton Bay data global model. Posterior distributions for species-specific precipitation coefficient parameter estimates were generated by summing estimates for the overall precipitation coefficient and each species-specific varying coefficient at each model iteration. Parameter means (circles) and 95% highest posterior density intervals (solid black lines) are shown. Species are listed in ascending order of mean species-specific parameter estimate. The mean overall precipitation coefficient estimate (−0.49) is shown as a vertical dotted line.
Contributor Notes
Associate Editor: J. W. Snodgrass.