Water metabolism of wolves in winter: Effects of varying food intake and exercise

Abstract

The only free water available to wolves during arctic winter is snow. Snow consumption involves an energy cost due to melting the snow and increasing the temperature of the resulting water to deep body temperature. Wolves are subject to negative energy balance when prey availability is inadequate. When negative energy balance is prolonged, the energy cost of snow consumption could shorten the time to death by starvation. It was therefore hypothesized that during negative energy balance in winter, wolves reduce energy expenditure by suppressing snow intake. The goal was to determine whether wolves conserve a significant quantity of energy by suppressing snow intake during negative energy balance in winter. The hypothesis was tested by varying food intake and exercise of captive wolves during winter in arctic Alaska. Experimental negative energy balance was imposed in three ways: (1) undernutrition, (2) fasting and (3) forced exercise on a treadmill with no change in food intake. Results of testing the hypothesis varied among experiments, but overall the findings refuted the hypothesis. When the wolves were undernourished, there was indirect evidence of suppressed snow intake. When the wolves were fasted, there was indirect evidence of enhanced snow intake. When the wolves were exercised with no change in food intake, there was indirect evidence of both suppressed and enhanced snow intake, but the evidence of enhancement was more conclusive. The indirect evidence of enhanced snow intake during either fasting or the exercise trial was sufficient to refute the hypothesis. The wolves did not conserve a significant amount of energy by suppressing snow intake. When snow intake was suppressed during undernutrition, less than 1% of the calculated daily energy expenditure was saved. There was no unequivocal evidence of snow intake suppression in any other experiment. It is concluded that when energy balance is negative during winter, wolves do not suppress snow intake to conserve energy.