Although spring may be springing for our Northern hemisphere readers, animals in the Southern hemisphere are preparing for winter. For nocturnal fat-tailed dwarf lemurs (Cheirogaleus medius) living in Madagascar’s western dry forests, winter means one thing: time to hibernate! Dwarf lemurs (Genus Cheirogaleus) are the only primates known to hibernate for long periods of time, and the fat-tailed dwarf lemur can hibernate for up to 8 months ! Hibernation refers to long periods when normally endothermic animals (animals that control their body temperature by generating body heat) drastically decrease their body temperature and metabolic rate. These periods of torpor are interrupted with “arousals” where the animal warms back up. While many animals go into torpor for short periods of up to one day, fewer animals engage in long-term hibernation like the fat-tailed dwarf lemur.
The stark seasonality characteristic of Madagascar’s western dry forests governs the timing of hibernation for fat-tailed dwarf lemurs. All of the rain for the entire year, which can be as little as 500 mm, falls within a 3–4 month span between mid-December and mid-March. This means that flowers and fruit, main food sources for dwarf lemurs , are only available during the rainy season. Thus, in order to conserve energy during periods of food shortage over the long dry season, the fat-tailed dwarf lemur goes into hibernation. To prepare for such a long hibernation, fat-tailed dwarf lemurs must fatten when fruit is abundant. Adults have been known to almost double their body mass—going from 130 g to 250 g (4.5 oz to 8.8 oz) in several months! As their name suggests, a lot of the fat is stored in their tail, which can increase from 10 mL in volume to 50 mL in volume  during this time.
Fat-tailed dwarf lemurs hibernate in tree holes , which keep them sheltered from the elements and from predators, such as birds of prey  and fossa . In poorly-insulated holes, the lemurs’ body temperature tracks the ambient temperature, much like ectothermic animals (often called “cold-blooded”, ectothermic animals rely on environmental heat to maintain their body temperature). In well-insulated holes however, the lemurs’ body temperature can remain more or less stable, with periodic spikes during arousals [7-8]. Interestingly, males emerge from hibernation first and begin patrolling their territory, which may serve to defend coming food resources from other groups .
Fat-tailed dwarf lemurs generally live in pairs (one adult male and one adult female), and offspring continue to stay with the parents for several years. These male-female duos are thought to be stable social pairs, despite a high rate (up to 44%) of extra pair copulations during the December–January breeding season . About two months later, 1–2 babies are born. Unlike many primate species, male fat-tailed dwarf lemurs engage in active care of the infants through babysitting, guarding, and accompanying them on initial foraging trips .
Fat-tailed dwarf lemurs still live in abundant numbers throughout the western forests of Madagascar, although like most lemurs, their populations are in decline. As fruit-eaters, they have an important ecological role in seed dispersal for the continued survival of the forests they inhabit . But until the fruits are ready to be eaten in the southern hemisphere’s summer, you’ll have to peer inside tree holes to find this unique, hibernating primate!
Meredith Lutz is a PhD candidate in the Animal Behavior Graduate Group. She’s interested in behavioral plasticity and social behavior. Her current research focuses on drivers of social plasticity in primates and takes her to Madagascar frequently.
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