When I think about hibernation, I picture a squirrel nestled in a tree or a bear in a cave, waiting out the winter. Primates don’t hibernate, and there would especially be no reason for tropical ones to do so, right? But in 2004, scientists discovered a lemur in western Madagascar that did, breaking the no-primate and cold-winter-only rules. The fat-tailed dwarf lemur uses hibernation — the state in which metabolic rates are lower, the animal’s core body temperature matches that of its environment, and certain physiological functions cease — to survive the dry season. The animals hide out in tree holes while temperatures are hot, water dries up, and food disappears, emerging months later when conditions are more friendly.
Now a group of scientists, from the United States, Germany, and Madagascar, report that they have found two more species of lemurs — Sibree’s dwarf lemur and Crossley’s dwarf lemur — that also hibernate. Their study appears in Scientific Reports.
These two species of dwarf lemurs live on the east side of Madagascar, in high-altitude rainforest. This area of the country also experiences wet and dry seasons, but the temperature variations here are greater. It never gets warmer than 85 degrees Fahrenheit and it sometimes reaches temperatures below freezing, making this one of the coldest places in Madagascar.
During the cold winters, the researchers found, the two eastern dwarf lemur species dig burrows into the moist, soft soil and wait out the cold. “Underground shelters provide effective insulation during cold winters, when the ground is frozen or covered by a thick layer of snow,” the researchers write. “In Madagascar’s eastern forests, burrows provide more insulation — i.e., more stable hibernaculum temperature than tree holes or nests.”
That stable environment helps the lemurs keep a more stable body temperature throughout the winter, when ambient air temperatures can fluctuate wildly. The hidey holes might also keep them safer from predators, the researchers hypothesize, particularly if the lemurs are most likely to get eaten when exiting or entering their places of rest.
Unlike the fat-tailed dwarf lemur, these eastern species have a hibernation that looks more familiar, like that of a squirrel or chipmunk. It’s not so surprising, though. The researchers even admit this in their paper. But it can be hard to give up the assumptions we make, especially about things we learn when we’re kids. (And by the way, bear hibernation isn’t as straightforward as you were taught either.)
Image of Non-hibernating Crossley’s dwarf lemur from Tsinjoarivo forest courtesy of K. Dausmann