| Mouse lemurs (Microcebus) are members of the nocturnal, small-bodied family Cheirogaleidae, the only primates currently known to use torpor and hibernation, a trait which seems to be more plastic in this clade than in other small mammals. All habitats of Madagascar go through a dry season from April to September each year, which can result in a period of fruit scarcity lasting up to 6 months, creating high selection pressure for adaptation to seasonal fluctuations in food availability. Previous capture-recapture studies have suggested a pattern of biased sex ratio throughout the dry winter as a result of females hibernating while most males remain active, with significant variation between species, study sites, and years. I have studied dry austral winter activity patterns in wild populations of Microcebus rufus in and adjacent to Ranomafana National Park, Madagascar as well as a captive population of a closely related species, M. lehilahytsara, at Zoo Zurich, Switzerland, using capture-recapture methods, radio tracking, and monitoring of habitat quality and ambient temperature, in order to determine how this behavior varies with sex, environment, and age in eastern mouse lemurs. Results suggest that the "ideal" winter behavior for both male and female mouse lemurs is hibernation, which is triggered by changing day length but hindered by high temperature and low food availability in the wild. The ultimate cause of hibernation in this clade appears to be avoidance of seasonal food scarcity. The proximate trigger of hibernation in captivity was photoperiod, as unlimited resources allowed fattening to occur in all individuals. In the wild, resources were limited, and hibernation was more plastic. Despite the abiotic changing of photoperiod at these sites, most mouse lemurs did not hibernate, likely because they had not put on sufficient fat. In both wild and captive conditions, most non-hibernators were offspring less than one year old, which likely have the most difficulty gaining enough fat for hibernation as they were born only a few months prior. Although eastern mouse lemur populations appear to be robust in disturbed habitats, temperatures and light levels in disturbed areas were higher, and preferred thermally insulated sleeping sites were less available, which may create conditions unsuitable for hibernation. |
