New research suggests lemurs use limestone caves as bedrooms.

"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," University of Colorado Boulder anthropology Associate Professor Michelle Sauther, who led the study, said in a news release. "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 caves could protect the lemurs from predators and humans as well as providing them with a temperature-controlled environment.

Researchers believe these animals have been using the caves as shelter for centuries but this is the first time it has been officially recognized.

The lemurs sleep in the canopies of trees when in a "gallery forest" near a river but in areas with spikier trees they turn to caves at bedtime. Spiny trees are not only more uncomfortable than other types, but are easier for predators to climb as well.

The team used field observations taken in a 104,000-acreTsimanampesotse National Park to make their findings. They took footage of 11 lemur tribes using motion-activated camera traps.

They noticed the lemurs' strange behavior when conducting their study near a spiny forest and limestone cliff.

"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," Sauther said.

Fusui langurs ("long-tailed Asian monkeys roughly two feet tall") and South African baboons have also been known to sleep in caves.

We think cave-sleeping is something ring-tailed lemurs have been doing for a long time," Sauther said. "The behavior may be characteristic of a deep primate heritage that goes back millions of years."