We might consider sleeping in the same bed every night as part of our natural routine, but the act of utilizing the same sleeping place has never been documented in primates — until now, that is. Scientists studying ring-tailed lemurs have now documented the first case of wild primates using the same caves and crevices for their nightly snooze.

"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," said Michelle Sauther, an anthropology associate professor at the University of Colorado Boulder who led the study.

"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 provide protection from potential predators, and they can provide water and other essential minerals. They also offer shelter from weather, as well as deforestation and other human activities that encroach on their habitats. Ring-tailed lemurs usually sleep high up in treetop canopies, but in forests with "spiny" trees, cave sleeping is preferable due to the comfort and added protection from predators that can easily scale the spiny trees. 

The study is the result of six years of observations on ring-tailed lemurs in the Tsimanampesotse National Park and the Tsinjoriake Protected Area in southwestern Madagascar. 

"They seemed to come out of nowhere, and it was not from the trees," Sauther 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."

Although this is the first documented case of primates using the same sleeping spots, the scientists are confident the behavior is more widespread, and that it has been going on for hundreds of years in Madagascar. 

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

You can read the full published study detailing the findings in the journal Madagascar Conservation and Development.