First Evidence of Primates Returning Home to a Cave Every Night Uncovered [VIDEO]

Madagascar's ring-tailed lemurs prefer to sleep in their own bed, according to the first study to uncover evidence of wild primates retiring to the same caves and crevices every night.

University of Colorado Boulder anthropology Associate Professor Michelle Sauther led the study published in the journal Madagascar Conservation and Development.

"The remarkable thing about our study was that over a six-year period, the same troops of ring-tailed lemurs used the same sleeping caves on a regular, daily basis," she said. "What we are seeing is a consistent, habitual use of caves as sleeping sites by these primates, a wonderful behavioral adaptation we had not known about before."

The researchers note that while the endangered Fusui langurs, long-tailed Asians monkeys that measure roughly 2 feet tall, have been found sleeping in caves, this behavior has been documented as a direct result of deforestation, with the monkeys traveling from cave to cave.

In contrast, the ring-tailed lemur has probably been sleeping in caves for millennia, according to Sauther.

Endemic to Madagascar, the animal weighs some 5 pounds and can reach up to 18 inches in length. They are highly social, often hanging out in groups of up to 30. They are unlike their other lemur peers in that they spend a significant amount of the ground where they feed on leaves and fruit, in addition to socializing.

Sauther and her colleagues first grew suspicious of the lemur's nighttime rituals after they found them on limestone cliffs next to so-called "spiny forests" where the trees' woody stems are covered in spines, rendering them less than ideal sleeping bunks.

"They seemed to come out of nowhere, and it was not from the trees," she said. "We were baffled. But when we began arriving at the study sites earlier and earlier in the mornings, we observed them climbing out of the limestone caves."

Returning to the same cave every night has its benefits, including body temperature regulation and ensuring nearby access to water and nutrients.

There is also evidence that some early human ancestors living in South Africa may have taken to caves for protection against predators, Sauther said.

"The behavior may be characteristic of a deep primate heritage that goes back millions of years."