Experts say climate change and deforestation mean the mammals are struggling to hibernate properly.
A group of Russian volunteers are caring for homeless bats who have woken early from hibernation. Experts say climate change and deforestation mean the mammals are struggling to hibernate properly.
One woman is leading a team in caring for the sleepy mammals and making sure they have enough to eat until spring arrives.
Elena Sherstyanyh keeps hundreds of bats in her apartment in Voronezh, Russia.
"It takes a lot of energy, a lot of time to nurse a bat. It needs specific knowledge. We can keep a bat only for a short period of time during the winter or while recovering from an injury. It is nearly impossible to create proper conditions for them, they need places with different moisture and temperature levels. Eating rations should have much in common with what they have in the wilderness," explains Sherstyanyh.
Sherstyanyh has been looking after bats for the last ten years. A biologist by training, she devotes her evenings and weekend to the tiny animals. She started by nursing around 50 bats a year, but those figures have now quadrupled to more than 200.
Warm winters without snow mean bats wake up from hibernation and, once awake, without enough food their chances of survival are diminished, says Sherstyanyh.
"Bats inhabit human buildings reluctantly. Deforestation is growing nowadays. In Voronezh, there have been wildfires and deforestation in recent years. The natural habitat for bats is rapidly declining," she said.
She adds that human disturbance is also disrupting bat hibernation. "The same is happening with those species that live in caves. Before only speleologists were going into the caves, they were trained and knew that it is forbidden to disturb bats, now everyone may enter caves."
A large bat colony was found inside the Voronezh hospital during repair work at the end of November 2018. Around 400 bats were found, but half were dead. All of those which survived were transported to Sherstyanyh's flat, and her neighbours donated three old refrigerators to make houses for them.
The refrigerators must be kept at 5 degrees Celsius and the doors can only be opened occasionally in order to maintain the temperature, but they are not airtight so the bats can breathe. Sherstyanyh says the main problem is maintaining the correct level of humidity, without which they will not sleep properly.
Bats in captivity should eat almost the same rations as in the wilderness, volunteer Anna Burkut explains: "We have trouble with some of them because they refuse to eat. We force them to eat as if they are children."
Every two or three weeks the bats are weighed to check whether they have enough fat for hibernation. Those who don't meet the weight requirement are taken out of the fridges and fed.
Olga Ilchenko is a fellow at Moscow Zoo's bat rehabilitation centre, who agrees that humans disturbing hibernating bats in caves is an issue.
"Natural habitats where they [bats] can freely live, eat and hibernate are violated. Humans are everywhere, tourists or others are interested to go to new places including caves," she explains.
"Speleologists know caves where bats are hibernating and they try not to disturb them, but unfortunately not everyone is behaving like that. As a result, many bats die when they are disturbed during hibernation."
Sherstyanyh releases her bats in springtime, when there is enough food for them to survive in the wild once again. All of the animals are fitted with metal rings so that they can be tracked after their release.