What do bats get up to during the winter?
Step into the secret world of bats this winter by tuning into the BBC's Winterwatch series filmed at the National Trust's Sherborne Park Estate. Here are five intriguing bat facts to whet your appetite.
How do bats prepare for the winter?
Bats fatten up on insects – they are big beetles fans – before the cold sets in. They will then live of their fat reserves during the winter months.
To conserve energy these warm-blooded mammals will drop their body temperature from around 34ºC to between 7ºC and 10ºC. They then look for a cool and dry place to roost and maintain the lower body temperature required for hibernation. Their metabolism slows right down and their heart rate falls to around ten beats per minute.
Asleep all winter? Fat chance…
Most bats start hibernating from September to March but only the lucky ones will have long periods of unbroken sleep.
While these adaptable mammals, which can drop their body temperatures to as low as 7 ºC to conserve energy, are pretty hardy they can only hibernate for long periods if their roosts maintain a cool and constant temperature. But if it gets too cold bats will have to use precious energy to find a new roost.
The lesser horseshoe bats at the Sherborne Park Estate in Gloucestershire love sleeping upside down inside the crevice of a tree or off the rocky ceiling of a mine in the disused quarry on the grounds.
Those that hibernate in cellars and old houses run the risk of having their roosts destroyed by human activity. Be extra careful when insulating your home and doing building work.
Bats are also occasionally woken up by their bodily functions, and are known to fly from their roosts to wee and poo before returning and settling back into a deep sleep, often referred to as a torpor.
Hanging on in there
Sleeping upside down is easy if you’re a lesser horseshoe bat. This is because they have hand-like wings that can grab onto surfaces and claws that lock them into position. Hanging upside down is not only a great way to hide from predators it's also the easiest position to take off from.
Getting ready for baby bats
Lesser horseshoe bats mate during the autumn but the babies are not born until the following June. The female bats store the sperm from the males inside their bodies throughout the winter and fertilise their eggs in April when the weather is warmer. But fertilisation is only successful if the female stays in tip top condition during the winter months.
Helping bats survive the winter
Loving bats means loving the landscape. The rangers at the Sherborne Park Estate take a number of measures during the winter to ensure the bats they love continue to thrive. Bats rely on echolocation (listening to the echoes of their calls coming back from nearby objects) to get around so the rangers work to ensure that landscaping is done with this in mind. Planting hedgerows and creating field margins can help bats orientate themselves and also attract the insects they like to eat.
You can help bats this winter by making a bat box in your garden and creating woodpiles to attract tasty bugs.
" Bats are a key indicator of how the landscape is coping. If there are lots of bats then there are lots of insects and we can tell how the whole ecology of the estate is getting on. "
Tune into BBC Two for Winterwatch to find out more about the secret life of bats, as well as a number of other fascinating animals, including tawny owls, badgers, red kites, skylarks and otters.
Chris Packham and Michaela Strachan are based at a barn on the estate, bringing updates from the remote cameras rigged throughout the surrounding countryside. Martin Hughes-Games hunts out harder-to-find animals, while Gillian Burke tracks down the animals that spend the winter on the island of Islay off the west coast of Scotland.
Winterwatch is broadcast on BBC Two on 29 Jan (2100); 30 and 31 Jan (2000); 31 Jan (2100); and 1 Feb (2100).