The role of the tail in temperature regulation of the cotton rat, Sigmodon hispidus

1. Metabolism, colonic temperature, body weight, water loss and temperature selection of normal and tailless cotton rats were measured at temperatures ranging from 4 to 36°C. 2. The metabolic rate of normal rats is significantly different from rats without tails at temperatures between 4 and 20°C. 3. Mean lower critical temperature of rats with tails is 30·8°C, while for rats without tails it is 30·0°C. 4. Colonic temperatures differ significantly between rats with and without tails at ambient temperatures from 4 to 20°C; rats without tails possess higher values. 5. Temperature selection was a significant inverse function of temperatures to which rats had been previously exposed. 6. Analyses of metabolic rate and temperature tolerance indicate that cotton rats are sensitive to low temperature extremes, and that other factors, i.e. changes in habitat or climatic temperature are playing a role in recent range expansion.