The secret life of bats in spring

Natterer's bat (Myotis natteren) hanging on tree trunk.

Spring is when our rangers check how bats are faring at the places we look after. Find out more about how we monitor and track these shy creatures.

Keeping count

The bat population at the Sherborne Park Estate in Gloucestershire is booming. This is because our rangers undertake painstaking work to count and track bats during the spring and early summer. The right measures can then be put in place to help bats find food and shelter. 

The first of three bat counts on the estate takes place at the end of May and sees a team of volunteers and rangers counting the creatures as they emerge at dusk from two maternity roosts. It’s thought there are as many as 160 bats hanging out in a disused kennel and a further 60 hiding out in a former Victorian bothy, both located in Sherborne. 

The final count in August will indicate how much the bat population at Sherborne has grown. By this time all the baby bats will have been born and many will be flying out of the roost for the first time.

Bechstein's bats can be found at Sherborne

The bat detectors

Special detectors are used to identify different species of bat by recording their calls, which are pitched at too high a frequency for the human ear. There are several different species of bat at Sherborne including lesser horseshoe bats, pipistrelles, bechsteins and serotines. Lesser horseshoe bats are the easiest to identify using bat detectors because of their distinctive warbling.

Staying on track

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.  

Mike Robinson, the area ranger at Sherborne Park Estate, monitors the flight paths of lesser horseshoe bats so that the right steps can be taken to help them.

The river is a good place to start tracking bats' movements as it is full of insects. Mike also waits patiently for bats to emerge from hollowed out trees and old abandoned buildings, both of which make ideal roosting sites. 

“The lesser horseshoe bat has a very light structure – its bones are like honeycomb. If they store too much fat they are too heavy to fly – not enough and they will exhaust easily and burn out," says Mike. "There’s a fine balance between using energy and storing it.”

The A303 passing close to Stonehenge

No easy road

Life can be hard if you’re a bat. Building developments and roads can destroy their roosts or disrupt flying routes, forcing them to take long and exhausting journeys to find food. Changes to the landscape, coupled with slow reproduction rates, means that bat numbers are falling in many areas of the country.

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.

Female lesser horseshoe bats typically give birth to one baby a year. A new born baby is around 20% the size of its mother and the birthing process can take several hours. 

Playing dead

To get winter-ready before the cold sets in, bats fatten up on insects – they are big beetles fans. They will then live off their fat reserves throughout the winter months. To conserve energy, these warm-blooded mammals drop their body temperature from around 34ºC to between 7ºC and 10ºC. They then look for a cool, dry place to roost and maintain the lower body temperature required for hibernation. Once settled, their metabolism slows right down and their heart rate falls to around ten beats per minute.

Group of Brown long-eared bats (Plecotus auritus) in loft space

Hanging in there

Sleeping upside down is easy for many types of bat. Their hand-like wings can grab onto surfaces, while their claws 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.