We are all used to the onset of winter bringing on a quieter season in wildlife watching, with many birds disappearing south to warmer climes, reptiles heading underground to escape the frost and invertebrates overwintering as larval forms or queens hidden from view. But on a warm winter day, sometimes wildlife can surprise you…
Some of our mammal species sleep the winter away, such as Hazel Dormice, Hedgehogs and bats, which enter hibernation for the cold winter months, surviving on fat reserves built up over the summer months. During this time, body temperature and metabolic rate are far lower than when they are active.
However, on a warm winter day, sometimes the rules go out of the window! If the temperatures are mild enough, it is fairly normal for mammals to stir from hibernation and even come out to feed. My colleagues and I from the Wildlife Trust of South and West Wales this winter have seen a large adult hedgehog out on Christmas Eve and bats flying during the day on the 29th of December.
As temperatures begin to lower, reptiles such as Adders and Common Lizards will head to sites called ‘hibernacula’, where they will spend the winter underground, sometimes in quite large numbers. They enter a state called ‘brumation’, which is similar to hibernation but they do not go into true sleep. Brumation is still typified by a decreased heart rate, temperature and metabolic rate.
It may surprise you to learn that even reptiles can be spotted in the winter if you know where to look! Adders are fairly hardy reptiles and on a sunny winter day with mild temperatures, they can be seen basking on the doorstep of their hibernaculum. A colleague of ours, Peter Hill from Amphibian and Reptile Conservation Trust, has even seen an Adder out on Boxing Day back in 2013!
For healthy individuals, occasional rousing from hibernation or brumation should not be harmful, but it does use up valuable energy. If winters are too mild, and animals are roused from hibernation too often, it can even be fatal. This is one reason why the potential for milder winters as a result of global warming is rather worrying.
How many of you have been surprised by winter wildlife that you didn’t expect to see? Let us know on our Facebook page.
Harris, S. and Yalden, D.W. Mammals of the British Isles: Handbook, 4th Edition. The Mammal Society.