The Thermal Dependence of Locomotion, Tongue Flicking, Digestion, and Oxygen Consumption in the Wandering Garter Snake

The body temperature ($T_{b}$) of garter snakes (Thamnophis elegans) can vary considerably in the course of a day (e.g., 4-33 C), and information on how $T_{b}$ affects physiological and behavioral processes is required to evaluate the significance of that variation. We measured crawling speed, swimming speed, tongue-flicking rate, digestive rate, and oxygen consumption at $T_{b}'s$ of 5-35 C in snakes collected in eastern Washington and acclimated to September field photoperiod and temperature cycles. All functions were strongly dependent on $T_{b}$. The maximum speed of crawling ($\bar{X} = 0.74 m s^{-1}$) occurred at $T_{b} = 34.5 C$; that of swimming ($\bar{X} = 0.69 m s^{-1}$) occurred at $T_{b} = 28.5$. At $T_{b} < 30 C$, the snakes crawled more slowly than they swam, but the reverse was true at higher $T_{b}$. At $T_{b} = 30 C$, the snakes moved their tongues up and down at a maximum rate of 22 Hz. Digestion rate increased sharply above 20 C, to a maximum of 0.45 mice/day within the $T_{b}$ range of 25-35 C. All snakes regurgitated their meal at 10 C. The $Q_{10}$ values for mass-specific oxygen consumption over the 5-15, 15-25, and 25-35 C $T_{b}$ ranges were 2.4, 1.3, and 5.0, respectively. Among the performances studied, swimming speed was the least sensitive, and digestion rate the most sensitive, to $T_{b}$. Field $T_{b}$ data indicate that all functions would be near maximum levels during the day but would be significantly reduced at night. We conclude that no single $T_{b}$ is best for the ecological tasks of prey capture, predator avoidance, and energy conservation.