Bats

Earlier this month, I had the chance to try something different at the nature reserve. An opportunity to join a guided walk, in search of bats. I enjoy seeing bats flitting about in the evening. But I hadn’t appreciated quite how interesting they are.

 

Bats are long time residents of the planet. Bat fossils dating back 52 million years have been discovered in the Green River area of Wyoming. Scientists believe that pressure of resources forced them to evolve into predominantly nocturnal creatures. While birds such as swifts and swallows had their fill of insects by day, bats became nighttime hunters.

There are over 1400 known species of bat in the world. Eighteen of these live in the UK, of which seventeen species are known to breed. Bats represent a quarter of the UK’s mammal species. The greater mouse-eared bat which used to reside in the south of England now number just two.

Fourteen varieties of bat live at the nature reserve. We hoped to see at least two of these on our walk, and possibly hear more. May is a time of high activity as the females start to form maternity colonies. Males are banished to their own roosts, leaving the females in the areas of highest food availability.

As sunset coloured the sky, we began our walk, sound monitors and speakers ready to capture ultrasonic calls.

Noctules

The first bats we heard were noctules. Flying higher than some bats, noctules are the UK’s largest bat. Owing to their flight path (high and straight, before diving for food), their size, and their visibility before sunset, they are sometimes mistaken for swifts. The noctule call is loud and low, compared to other bats, meaning children can sometimes hear them unaided.

Pipistrelles

Next, and slightly later, we heard and saw the pipistrelles. Common pipistrelles are the smallest bats in the UK. Their cousin, the soprano pipistrelle, is slightly larger but it is otherwise very hard to distinguish visually between the two. The soprano’s ultrasound call is at a lower frequency than the common pipistrelle making it possible to differentiate using bat detecting equipment. A soprano pipistrelle can eat up to 3,000 insects a night! Where noctules fly high and straight, pipistrelles dart in smaller movements at a lower height.

Hearing

The monitoring equipment we used translates bat calls to a lower frequency, meaning they may be heard distinctly from one and other. The frequency of the call varies between species, and is adapted to suit the bat’s environment. They do this to differentiate between objects, and prey.

Each bat has its own unique call so they avoid confusing one and other through echolocation interference. A few milliseconds before calling, a muscle of the middle ear contracts to dampen the effect of the strong sound. Shortly afterwards, it relaxes, and the bat can receive the echo of the call through its specially shaped ears. The bat translates the sound into information about the size, shape, and direction of its surroundings and prey.

Daubenton’s

Finally, we left the darkness of the woods and returned to the lake. It was almost ten o’clock by now, and the Daubenton’s bats were about. Named after 18th century naturalist, Louis-Jean-Marie Daubenton, this bat is also known as the ‘water bat’. The Daubenton’s flew fast and low over the water, their pale coloured bellies catching the torchlight.

Having thoroughly enjoyed my first bat walk, I have joined the local bat group and signed up for the next walk. If you’re interested in bats, I recommend booking onto something similar if you have the opportunity.

Links

Find your local bat group: https://www.bats.org.uk/support-bats/bat-groups
More information about bats is available through the Wildlife Trusts, and the Bat Conservation Trust.