Correlations between body temperature and environmental factors and their variations with activity in garter snakes (Thamnophis)

Abstract

The aim of this study was to determine the extent to which several environmental variables were associated with body temperatures of three species of garter snakes (Thamnophis) on Vancouver Island, and whether or not these associations changed with different activities of snakes. Perhaps because the data set was quite heterogeneous, no differences were observed between body temperatures of different species or sexes. In all activity groups, environmental temperatures were the variables most highly correlated with body temperatures; factors such as visible light intensity and cloud cover also were correlated with body temperature in some cases, but added little to the "explained" variation of body temperature. There was little evidence of seasonal or diel fluctuation in body temperature, but more careful data collection may be required to detect these. The correlation between body and environmental temperatures was highest for snakes under cover and lowest for moving snakes. Basking snakes in general were intermediate between these two groups, but snakes basking in the sun under sunny skies showed low correlation between body and environmental temperatures. Snakes, therefore, had body temperatures relatively independent of environmental temperatures under certain circumstances, but conclusions about thermoregulation could not be drawn from these data.