The gray mouse lemur (Microcebus muriosus) can also hibernate for months, but in this species only adult females do it. Like their fat-tailed cousins, female gray mouse lemurs go through their reproductive cycle between late December and early February, aquiring impressive amounts of fat and increasing body mass by more than 40 percent. As the nights begin to get cool, these two-ounce lemurs resort to another remarkable strategy to reduce energy expenditure: night-time torpor. When the temperature falls below a certain point, they enter a tree hole and reduce metabolism, thus lowering body temperature close to the level of air around them. (Some of our colleagues have reported body temperature as low as 48°F in torpid animals.) Huddling together in well insulated holes further enhances their energy savings. When the ambient temperature rises during the morning, body temperature follows passively up to about 82°F, at which point the metabolism kicks in again and heats the lemurs up to a normal level of about 100°F. As the dry season progresses, adult females stop leaving the tree hole altogether, remaining inactive for the next four months or more. Males, however, continue venturing out to forage (mainly on gum and the few remaining insects) for at least a few hours almost very night. Why they forgo the substantial energy savings enjoyed by females and expose themselves to owls and other predators every night is something of a mystery to us. However, the mating season begins soon after the female emerge, and we think the males may be taking advantage of these months to establish dominance hierarchies.