PARIS – Scientists curious about the wintertime vanishing act of a type of Madagascar dwarf lemur were astonished to find the animals burrowed deep into the soil, curled up for a months-long sleep.
The discovery, announced in a study published in Nature Scientific Reports on Thursday, makes the island country’s eastern dwarf lemurs the only primates in the world known to hibernate underground.
The fat-tailed lemur, a cousin from the slightly warmer, drier forests of western Madagascar, was already known to hibernate in tree holes for about seven months of the year. Researchers long suspected the eastern lemurs may be doing the same but could never find them.
“You don’t see them, trap them or find them during the dry season (wintertime) while walking the forests at night,” said study coauthor Marina Blanco of Germany’s Hamburg University. “They had to go somewhere . . . .”
And so the team fitted radio transmitter collars on 12 lemurs from two eastern species in summer, and waited. The species, Sibree’s dwarf lemur and Crossley’s dwarf lemur, live in the forest of Tsinjoarivo. Setting out in winter with signal trackers, the team fully expected to find the lemurs sleeping in tree holes.
“We were tracking the collar’s signal and pointing our antenna up in the air, toward the tip of a tree. But the signal was coming from the ground, so we thought the animal had lost the collar,” said Blanco. “We looked around and didn’t see anything, so we started to dig up the area and found a furry ball: The dwarf lemur was curled up and cold to the touch, still wearing its collar.”
The animals hibernated for anything from three to six months after burrowing 10 to 40 cm under a spongy layer of tree roots, soil and decaying plant matter. The tiny bundles weighed about 250 to 350 grams, depending on which species they belonged to.
It is uncommon for primates to hibernate — in fact, the western fat-tailed lemur was previously the only primate known to do so. It is also rare behavior for animals in tropical regions — residents of colder climes such as polar bears, hedgehogs or squirrels are usually the ones who find it necessary to hide out during wintertime.
During hibernation, the metabolism slows down and the core body temperature reaches ambient levels, meaning the body has to work less hard to stay alive. During the Madagascar winter, lemurs are exposed to drastic daily temperature fluctuations of as much as 30 degrees Celsius. In the highland rain forests, ambient temperatures can drop to between zero and 5 degrees in winter — cold for animals used to summer averages in the 30s.
In retrospect, the team wrote, underground hibernation in the tropics makes sense, as it provides better insulation than tree holes or nests.