The Science of Christmas: Why do some animals sleep all winter?
What animals do you usually find on a Christmas card? Most likely it will be white foxes, deer with antlers and robins. Why not bats or hedgehogs?
Well, at Christmas time in the northern hemisphere these mammals are (or should be) hibernating. True hibernation is when an animal drops its temperature to be within 1-2pc of the surrounding ambient temperature, its metabolism and heartbeat slows down significantly and fat stores rather than glucose are used for energy. They stay in this state for long periods of time.
Bats hold the record for mammal hibernation with some bat species only taking a breath every two hours and hibernating undisturbed in a lab for over 300 days. Essentially these animals are in suspended animation.
But why do they do this? In winter the temperatures are colder and the food resources are not available. Bats and hedgehogs feed on insects and usually there are very few insects available at Christmastime. We require food so that our cells can function. One strategy to survive a food-scarcity is to slow down all cellular processes — this is hibernation. It is an amazing physiological trait and many scientists are trying to understand how hibernation has evolved and why only some species can do it. Indeed, it has been suggested that if humans were to achieve space travel we would have to learn how to hibernate to survive the trip.
True hibernating mammals look like they are frozen dead and can take up to 30 minutes to arouse. If you were to walk into a large cave in America, where bats hibernate, and shine a torch at the ceiling, you would see hundreds of bats clustered together, completely still, looking like Christmas baubles glistening in the light reflected from the tiny ice particles on their fur. These are very special places know as hibernacula. The temperature and humidity is just right to let the bats go into hibernation, without which they cannot survive the winter.
We know very little about where Irish bats hibernate and, indeed, if all nine Irish resident bat species actually stay in Ireland over the winter.
At the Centre for Irish Bat Research at UCD we are trying to find Ireland’s hibernacula, which are key conservation areas that need to be protected and conserved.
This Christmas when we are tucking into our dinner — since we have enough food not to hibernate — we should think a little. As global temperatures are predicted to rise, in the future perhaps Ireland will become too warm to enable animals to hibernate. Maybe we will have Christmas bats and hedgehogs, which, although eye-catching on a card, would be an environmental disaster.
If we work together we can better tackle and resolve our imminent climate crisis. Let’s make a 2016 New Year’s resolution to do so.
Professor Emma Teeling, School of Biology and Environmental Science, University College Dublin