Primates Called Pygmy Slow Lorises Take Long Wintertime Naps, Making Them First Hibernating Primates Outside Madagascar

As cold weather sets in, bears crawl into their dens, bees fly into their hives and groundhogs burrow underground as part of a survival process knows as hibernation. Basically, hibernation represents a state of energy conservation during which body temperature and metabolism are drastically reduced. While hibernation is common for many animals, it is rare among primates.

Previously, researchers believed the only primates capable of hibernation were three types of lemurs that exclusively live on the island of Madagascar and tend to bunker down during the dry season to conserve water. However, a new study has confirmed that another primate, the pygmy slow loris (Nycticebus pygmaeus), takes an unusually long nap in the wintertime, too.  

"Our new finding of a hibernating primate species outside Madagascar sheds new light on the evolution of hibernation," Thomas Ruf, first author of the recent study from the Research Institute of Wildlife Ecology at the Vetmeduni Vienna, explained in a news release. "Possibly, hibernation as an overwintering strategy was lost in other primates in Africa, Asia, and the Americas. However, perhaps hibernation is also used by further primate species, which have not been studied yet."

For their study, researchers monitored body temperatures of five pygmy lorises, residents of a Vietnamese primate reservation, during the fall, winter, and spring. As it turns out, both males and females partook in repeated hibernation episodes lasting up to 63 hours between December and February. Any resting state lasting longer than 24 hours is considered hibernation. Researchers believe this behavior is triggered by an internal clock that induces energy conservation when food resources and local temperatures decrease.

"In Vietnam, where we studied the animals, there are pronounced seasons. Ambient temperature can drop to five degrees centigrade. This is exactly when the probability of animals entering a hibernation episode was highest," Ruff explained. "There had been anecdotal observations of pygmy lorises that remained inactive for several days. Occasionally animals were encountered that felt cool to the touch. However, we discovered only now that the lorises actually hibernate."

The pygmy slow loris is a relatively small animal that belongs to the so-called wet nosed classification of primates. Typical facial features include large eyes, a white stripe running from the nose to forehead, and a dusting of silvery gray fur over an otherwise all-brown coat. The tree-slinging animals are also nocturnal and native to Southeast Asia.

Their findings were recently published in the journal Scientific Reports. 

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