Forest microenvironments and resting energetics of the American marten Martes Americana

To determine whether American martens Martes americana behaviourally thermoregulate in winter, and to estimate the energetic cost of resting in various forest microhabltats, we studied microenvironments used by martens in a coniferous forest in the Medicine Bow Mountains, Wyoming We hypothesized that martens would rest in sites that minimized energetic costs, and that the relative thermal efficiency of sites would vary as a function of snow depth and weather By measuring heat loss from a heated model and calculating operative temperature, we found that equivalent marten metabolic rates were inversely related to operative temperatures Operative temperatures were generally higher outside resting cavities than inside, except when snow was > 15 cm. outside air temperature was ≤−5°C. and wind was ≥0.3 m s −1 For the models lying on a snowy substrate, total body conductance was 0 32 W °C −1 23% higher than with the models lying on dry wood chips The microenvironments of resting sites and the preferences of martens generally are consistent with our hypothesis of behavioural thermoregulation Conductance contributed strongly to total thermal losses and to explaining selection of resting sites We propose a decision tree to predict where American martens should rest under a range of environmental conditions