Animals maximize fitness by choosing their surroundings, including shelters for resting phases. Cheirogaleus medius is a small, nocturnal Malagasy lemur that hibernates in tree holes for up to 7 months a year. I compared certain characteristics of tree holes used during the active season with those used during the hibernation season to assess their relative effectiveness in reducing energy expenditure and predation risk. The tree holes chosen as hibernacula only differed from those used for diurnal rest in their tendency to be located in larger trees. Large, wellinsulated trees would allow a better controlled pattern of energy expenditure in hibernating animals rather than decreasing total amounts of energy expended.