The effects of feeding and ecdysis on temperature selection by young garter snakes in a simple thermal mosaic

Abstract

Temperature selection by five young common garter snakes, Thamnophis sirtalis, was studied using a simple, two-choice thermal mosaic. The animals were housed in an arena (60 × 120 cm) within an environmental room, where they were exposed to a photoperiod of 12 h light: 12 h dark and a general ambient temperature of 20 °C. The arena contained two shelters (20 cm × 20 cm), one at ambient temperature and one heated to 30 °C. On a given day, we determined the snakes' locations in the arena twice an hour for several hours. Observations were made in this manner on most days over a period of 19 weeks. Within 1 h following a late afternoon feeding, use of the hot shelter increased from about 5–20% of observations to above 80%. Occupation of the heated shelter remained at a high level the next day and then decreased, reaching a background of 10–40% by the 3rd day after feeding. The animals displayed a higher background use when maintained on a weekly feeding regime than they did when on a biweekly regime. During a 5-day period preceding ecdysis, occupation of the hot shelter again exceeded 80% of observations; decline to a background of 0–10% began about the day of molt. Runs tests performed on the daily records of individuals indicate that hot-shelter use tended to occur in bouts. There was no suggestion of diurnal variation in thermoregulatory behavior.