The sleeping habits of a tiny bat may change our understanding of mammalian hibernation, Israeli researchers say.
Hibernation was believed to occur only in low temperatures, as mammals sleep through three to nine months of cold and hazardous winter with a very low heart rate and body temperature.
But this is not the case in two species of the mouse-tailed bat (the Rhinopoma microphyllum and the R. Cystops). Tel Aviv University researchers who were trying to find where these bats disappear every winter discovered them hibernating in warm caves with temperatures of 68°F (20 degrees Celsius) in the Syria-African Rift, a northern extension of Africa's Rift Valley.
Professor Noga Kronfeld-Schor, Chair of the Department of Zoology at the university's Faculty of Life Sciences, and doctoral student Dr. Eran Levin were surprised to discover that from October to February, these bats were in a deep sleep, breathing only once every 15-30 minutes, with extremely low energy expenditure. Most hibernating mammals usually breath more frequently.
"The surprising thing was that these animals hibernate at high temperatures. This changes the whole concept of hibernation because people consider hibernation as a strategy to cope with very cold winter conditions, with snow, no food available. And here we have bats hibernating at warm temperatures, which is really surprising," said Kronfled-Schor, whose research was published in 'Proceedings of the Royal Society of London'.
The researchers monitored the bats' behavior in a number of ways - using temperature sensitive transmitters that measured their skin temperature in the caves and then brought some back to a laboratory to measure their metabolic rates and evaporative water loss at different temperatures.
The bats also did not eat or drink during this time, the researchers said.
Their average skin temperature in the caves dropped to 71.6°F (22 degrees Celsius) and their metabolic rates reached a minimum, according to the research.
Israel's winter, although mild, was apparently too cold for the bats as it is the northern edge of their world distribution, Kronfeld-Schor said, adding that they seemed to choose specific caves with especially warm temperatures for their hibernation.
"What we found was that these bats do not hibernate in just any cave. They hibernate in specific caves along the Syrian-African Rift Valley where very hot and humid air comes from the ground. And we think that they choose these specific caves because temperature never drops below 20 degrees Celsius. This is the northern edge of their world distribution, which means that usually they are exposed to much higher temperature and probably the winter in Israel although it's very mild is still too cold for them to be active," she said.
Approximately four weeks before hibernating, Kronfeld-Schor added, the bats also changed their nutrition habits to gain more fat, feeding only on queen ants with wings to gain a 50 percent increase in body mass.
The discovery may pave the way for better conservation of this insect eating bat species, which is important for natural pest control, Kronfeld-Schor said.
"The fact that these bats need to use these warm caves in order to survive winter and perform hibernation means that we have to protect these caves and include them in nature reserves. And we've been working with the Nature Reserves Authority in Israel in order to establish nature reserves around these caves," she said.
According to the IUCN Red List of Threatened Species, human disturbance in roost sites and use of pesticides for locusts affect this bat species and should be minimized.