The Sid Valley is home to twelve different species of bat and the Biodiversity Group is helping to locate these amazing creatures as the bats fatten themselves ready to hide away in hibernation.

Ed Dolphin writes for the Sid Valley Biodiversity Group.

Bats are aerial acrobats, the only mammals that can truly fly, but they are not as blind as the common idiom would have you believe. We on the other hand usually have real trouble seeing them because our night vision is so poor and we become ‘as blind as bat’ after dark when most bat activity takes place.

Bird watchers can often identify a bird by its call without seeing the bird. Bats have distinctive calls and bat watchers would like to copy the bird watchers but our hearing is as useless as our night vision because most bat calls are ultrasonic, outside of our hearing range.

Luckily, we have technology and we can record the bat calls and then translate them into audible sounds or visible patterns on a screen. The Devon Bat Survey, coordinated by Devon Wildlife Trusts and the Devon Biological Records Centre (DBRC), has been doing just that for the last eight years tracking the various populations around the county.

An ultrasonic sound recorder is left out for three nights at a likely location. Bats like to hunt in places away from civilisation with good hedgerows or lines of trees, or near the banks of a river, places with a good population of flying insects. A tiny Pipistrelle, half the size and a quarter of the weight of a wood mouse, can eat as many as 3,000 insects in a night.

The recorded calls, often several thousand over the three nights, are then scanned by an AI program that sorts the different calls, assigning a level of certainty to each one. If the program is more than 70% certain, the identification is accepted as reliable by the DBRC.

This year, volunteers from the Sid Valley Biodiversity Group have taken part in the survey. At the end of September, a recorder was left out on an organic farm just above Sidbury. The site had everything a bat could ask for, plenty of trees near the river and some very old barns with lots of nooks and crannies for roosting.

We were worried that the poor weather might restrict the bats’ activity but we were delighted by the results, with over 1,200 calls recorded, there are obviously plenty of bats in the area. Not just plenty of bats but a wide range of species. The AI picked out nine different species of bat but three will need to be verified by an expert listening and looking at the call pattern on a screen.

The bulk of the calls were identified as the two commonest UK species, Common and Soprano Pipistrelles. Also Natterer’s, Serotine and Lesser Horseshoe bats were picked up with some certainty. Other recorded calls suggest the site is visited by Greater Horseshoe, Noctule and Brown Long-eared bats.

There was one call that sounded like a Daubenton’s bat. These are river specialists, flying just above the water and picking insects off the surface. There are several that feed regularly in The Byes and they are probably found further upstream, but the farm is some way from the river and so Daubenton’s bats will not visit very often.

Up until the Millennium several UK bat species were suffering because of roosting habitat loss and the decline in flying insects that many people have written about. Fortunately, national monitoring projects of the last few years have seen an increase in most UK bat populations. New legislative protections for the bats themselves, and other projects promoting insect biodiversity such as leaving grass areas uncut seem to be working. Let’s hope our beautiful valley can continue to support these mysterious but amazing creatures.