We have many fine trees around our town, one of the things that makes Sidmouth a pleasant place for humans to live, but we are not alone in enjoying our treescape. If you go for a walk around many areas of the town at and just after dusk, you will see bats fluttering about above your head feeding on the insects that fly around the trees.
Bats are amazing creatures. They are the only mammals that truly fly, they adjust their body functions at different times of the year, they cooperate in and around their roost sites, and they can locate a small moth flying nearby even in the dark.
Despite the adage, bats are not blind but their echo location is the main sense when they are hunting. They send out series of squeaks and clicks and judge objects around them by picking up the echoes. Most of the calls are ultrasonic, well beyond the range of human hearing, some children can hear some of the calls, but most of us cannot hear them. This is where technology comes to our aid.
Bat detectors pick up the bat calls and convert them to sounds that we can hear. The latest detectors also present the signature of the calls on a screen. It still needs some expertise to listen to and identify the adjusted calls and the screen displays. Step forward AI, yes it does have some genuine uses.
Sonograms of a Common and Soprano Pipistrelle
The British Trust for Ornithology Acoustic Pipeline system has analysed many thousands of recordings, originally bird calls but now bats also, and can be used to link sounds and species. It goes further, it gives an estimate of how certain that identification can be.
Using an Echo Meter Touch 2 attached to a smart phone, we have been recording the town centre bat populations. Two of Britain’s smallest and commonest bats, the common and soprano pipistrelle can be detected almost anywhere where there are large trees including around the bus stops on the Triangle.
The table below shows the species we have recorded in the last week at various sites around the town. In each case the recordings were taken from soon after sunset at about 9.30pm until about 11.30pm. The decimal figure is the highest certainty rating for each species, those marked low should be discounted for now but might be upgraded in later recordings.
The Grey Long-eared Bat has a caution tag because, although 0.72 is a good level of certainty for the AI system, the species is rare but there are colonies known in Devon and they do range up to 6km on their feeding forays. It will be interesting to see if we make repeat recordings.
Leisler’s Bat is also not very common. They are called the ‘hairy-armed bat’ because of their long fur around the shoulders akin to a lion’s mane. Nathusius’ Pipistrelle is another rarity, a migrant visitor from eastern Europe.
The Bat Conservation Trust tells us the Serotine Bat is one of Britain’s largest bat species and usually one of the first to appear in the evening, often emerging in good light. Its broad wings and a leisurely, highly manoeuvrable flapping flight with occasional short glides or steep descents are distinctive.
Recently, I was sat on the bench in the lawn area of Glen Goyle just after sunset and a serotine bat swooped straight at me and almost parted my hair. I wasn’t worried, it just isn’t true that bats will get tangled in your hair, their echo location is too good for that to happen.
Glen Goyle is such a good site because it is the focus of more than one habitat. You have the many-tree’d gardens on Glen Road and the tree-lined Bickwell Valley close by. There is also the open space of Bickwell Meadow across the road and the running water of the brook. This last is probably why there are Daubenton’s Bats. This species specialises in skimming insects from the surface of water. They are one of the species recorded regularly in the Byes. The Friends of Glen Goyle have worked with EDDC to install a range of bat boxes among the trees of the Goyle, hopefully this will make it an even better habitat for these fascinating creatures in years to come.
As a bonus, the bat detectors also pick up the ultrasonic squeaks of other small mammals. We now know that there is a colony of common shrews active in Blackmore Gardens at night and dormice live around Sidmount in Station Road.
We will be recording in other areas around the valley and revisiting the listed sites in the next few weeks, look out for updated results here.
Update on the bats recorded so far. The decimal figure is the AI assessment on reliability of the identification, some of which are too low to be accepted, but later recordings might confirm them.
Related Posts:
