Until now, hibernation was thought to be a biological strategy used exclusively during cold winter months. As such, places like the Middle East, where winter months are mild, aren't ideal for discovering hibernating mammals.

But researchers from Tel Aviv University recently found two species of the mouse-tailed bat hibernating in caves in Israel's Great Rift Valley. The bats' sleeping quarters featured a constant temperature of 68 degrees Fahrenheit. It's the first time a mammal has been found hibernating in consistently warm temperatures.

The bats -- Rhinopoma microphyllum and R. Cystops -- were observed hibernating from October to February. During their time asleep in the caves, researchers found the hibernating species only breathed once every 15 to 30 minutes.

"Hibernation in mammals is known to occur at much lower temperatures, allowing the animal to undergo many physiological changes, including decreased heart rate and body temperature," lead study author Noga Kronfeld-Schor, a zoologist at Tel Aviv, said in a press release.

"But we have found these bats maintain a high body temperature while lowering energy expenditure levels drastically," Kronfeld-Schor said. "We hypothesize that these caves, which feature a constant high temperature during winter, enable these subtropical species to survive on the northernmost edge of their world distribution."

The researchers also found that the bats didn't take team to eat or drink during the hibernation period, and that the species lowered their energy expenditures without lowering their body temperatures.

"The second main finding is that hibernating animals don't need to lower their body temperatures in order to lower their energy expenditure," Kronfeld-Schor said. "These bats exhibited dramatic metabolic depression at warm body temperatures in the hottest caves in the desert."

Researchers discovered the two species prepared for hibernation by altered their diet before winter, eating only queen ants. The switch from unsaturated to saturate fats allowed for a 50 percent increase in body mass.

The study was published this week in the Royal Society of London journal Proceedings B.