Brown long-eared bats are a medium-sized bat, with a head and body length of approximately 45mm long. However, it’s ears are nearly as long as the body.
Head & body length: 37mm – 52mm
Forearm length: 34mm – 42mm
Wingspan: 230mm – 285mm
Weight: 6g – 12g
Thumb: More than 6.2mm (in comparison with grey long-eared)
Tragus: Greatest width less than 5.5m (in comparison with grey long-eared)
Colour: Adults have light brown fur, pale underneath; juveniles greyish –
beware confusion with grey long-eared!
Brown long-eared bats are slow-flying and highly manoeuvrable bats, with short broad wings. This means that they are able to pick off insects from trees and foliage, a behaviour called ‘gleaning’. They are even known to be able to hover in flight.
Often called ‘whispering bats’ they echolocate at a very quiet level. They have evolved the ability to do this thanks to their oversized ears, which allow them to hear both the faint echolocation pulses as well as the minuscule sounds produced by their prey itself. This means that they can hunt without even echolocating at all.
Although, like a lot of bats, they will eat insects on the wing, they also often consume larger insects from ‘feeding perches’, locations where bats can hang and eat prey safely . Perches can often be found inside barns, porches, or even pergolas. You can recognise these perches by the accumulation of insect remains, in particular moth and butterfly wings. One of their favourite prey item is the yellow underwing.
Brown long-eared bats are very closely linked to woodland, their roosts usually being found within 250 metres of woodland. Their summer roosts are often found in old buildings, typically barns, churches, old houses and sometime trees. They select locations with large loft spaces or similar open internal spaces. This is due to their habit of ‘light-sampling’ before emerging from their roosts. This is a behaviour whereby they fly within the roost building before emerging outside, so that they can test to see if it dark enough to emerge (Brown long-eared bats emerge late, up to an hour after sunset). This pre-emergence flight may also serve to warm them, and their huge ears, up before foraging. During the day, in order to retain heat, brown long-eared bats drain the blood from their ears and tuck them under their wings, often giving the appearance of a bat with much smaller ears.
They form relatively small colonies of about 20 animals. However, they can be quite obvious, as they roost amongst the wooden beams of a loft space, and therefore can be easily seen, when present.
In the winter, they roost in caves, tunnels, and other underground places, as well as tree crevices. We often find them in Link Pot, in the Easegill system on the eastern border of the county.
Brown long-eared bats echolocate from 25 – 50kHz and peak at around 35kHz. When listening on a bat detector, the calls are very quiet and sound like a series of dry, light clicks.
Brown Long-eared bats are found throughout the UK and are common in Cumbria. The presence of many stone barns and old buildings with large loft, as well as the large areas of woodland in the county mean that they are widespread in the South Cumbria area.
However, brown long-eared bats have declined in Britain as a consequence of changing land use, modern agricultural practices, and the fashion of converting barns and old houses They can be particularly susceptible to pesticides, especially their use in roofs where it often roosts on exposed timbers.