I love this time of year. The birds begin gathering the dead twigs and leaves from my garden, the blossom starts to form on the tree just outside my office window, and the buds on my daffodils look set to display their sunny yellow petals at any moment. I also love sunset at this time of the year, looking hopefully into the sky for signs of the first emerging bats of year from nearby rooftops and trees.
Our 18 species of insectivorous bats have been in hibernation since around October / November last year and now is the time to start watching for their return to our skies. The hibernation process is actually quite gruelling for these beautiful creatures and their ability to withstand very low temperatures with no or limited food for approximately four months each year is most impressive given their small size.
Our largest bat (the Noctule) is still small enough to sit in the palm of your hand and our smallest (the Pipistrelle) could probably fit into a small matchbox. Yet this tiny Pipistrelle bat has a very large appetite, consuming up to 3000 insect in just one night. During hibernation this sizeable appetite has to be forfeited as bats go into a state of torpor where their body temperatures drop and they are forced to use stored fat (from all those midges) to keep them alive. What an incredible feat for something so tiny!
Whilst some bats like to keep their friends close and hibernate together, some may choose to hibernate alone. Sites are generally chosen for their coolness, quietness and high humidity levels, in case of a quick drink during hibernation. The image below (by Yves Adams) shows Natterers bats during hibernation, huddling together like little cottonwool balls. Dew drops gather on some bats and although this looks relatively humorous to us, it is essential to their survival.
I will continue to look out of my window every night at dusk, searching for that first tiny black dot swooping across the sky. A sign that bat survey season is not far away. Do take the time to sit and watch the sky yourself, even if you are in the middle of London. You will be very surprised where they turn up!
If you love bats then why not contact the Bat Conservation Trust and help out with their annual National Bat Monitoring Programme or even just go along to one of their bat identification courses?