Bats make the most of late summer insects

Our local bats seem to have been busy of late. Each evening, just as dusk starts to settle over the town, two or sometimes three bats can be seen, each silhouetted against the last of evening’s light. There are two species that make use of our garden, something confirmed through chance encounters with individuals perched on walls or, in one case, caught in a mist net set for roosting thrushes. By far the commoner species is one of the pipistrelles, most likely the soprano pipistrelle. Up until just a few years ago it was thought that there was just one species of pipistrelle in Britain, then it was discovered that this one species was in fact two. One of these, the pygmy pipistrelle, tends to occur in smaller colonies in more rural areas, while the other, the soprano pipistrelle, forms larger colonies and often roosts in houses. In 2001, a third species, Nathusius’ pipistrelle, was found apparently breeding in east Norfolk. It’s presence was revealed by Susan Parsons who had picked up the species’ social calls on a bat detector used to monitor the colony of barbastelle bats at Paston Barns.

The other species using my garden is the brown long-eared bat, a highly distinctive species within the county; its close relative, the grey long-eared bat, is restricted to a small area in the extreme south of England. As their name suggests, long-eared bats can be distinguished from all other British species by their enormous ears, which are joined at their inner bases. These ears are used by the bat to pick up “reflections” which bounce back from objects caught in the bat’s weak echolocation pulses. Brown long-eared bats are leaf gleaners, typically hunting in lightly wooded areas and taking moths and other insects from the surface of leaves. The tall sycamore in our neighbour’s garden appears to form part of the hunting beat used by one or more of these bats, and they can be seeing making relatively slow passes around the tree. The flight of the local pipistrelles has a more frantic feel about it.

I have encountered brown long-eared bats on and off over the years. The species had both a breeding colony, some 40 to 60 strong, and a winter hibernaculum at Wolterton Hall in north Norfolk, where I used to live. In the summer moths, the breeding females and their young occupied the attic space above the old stable block, while in winter they were to be found in the cellars under the hall – where temperatures were buffered against outside ambient fluctuations. Nowadays, I only tend to see one close-up when it perches on the sheltered wall of my side passage to dismember a moth.