Cornwall Mammal Group

One of the smaller British bats, weighing less than 9 g and with a wingspan of 250 mm, the lesser horseshoe is confined to Wales and the west of England. Lesser horseshoes hunt in sheltered valleys and
woodland, often near water. During

daylight hours they roost, usually in old buildings, hanging upside down, with their wings wrapped around their teaspoon-sized bodies. Seen close-up, this tiny bat has greybrown fur and large triangular ears which, unusually for a bat, are very
mobile.

 

The complex U-shaped noseleaf, which gives the horseshoe bats their common and scientific names, is a key part of their echolocation system - emitting and controlling a cone of ultrasound. It also allows horseshoe bats to echolocate 

even when they are carrying prey in their mouths. As with most bats, they are most likely to be identified using a bat detector to pick up the sounds that
they use for navigation and hunting. The lesser horseshoe produces a constant high
frequency warble at 110 kHz. The bats use the Doppler shift, detecting a change in
frequency of the sound reflected by moving prey. Heard on a heterodyne bat detector the lesser horseshoe sounds rather like a Dr Who sound effect!

During the summer lesser horseshoe bats spend their days roosting in old, undisturbed
buildings, particularly old churches and farm outbuildings. They fly directly to their roosting site where they hang upside down, so they need suitably large entrances and roof spaces. Mating occurs in the autumn and the female stores the sperm until the spring. Pregnancy takes about 78 days and the young are born in July/August. While males are often solitary, females congregate into maternity colonies and they may huddle together in cold weather. At first the mother may carry the single pup with her whilst foraging, but older juveniles stay in the roost. From October the bats move to winter roosts (usually within 5 km of the summer roost), 

where they hibernate in groups of up to several hundred. Hibernation sites need to have constant low temperatures but high humidity. In Cornwall many horseshoe bats use old mine
workings, but natural caves and old cellars are also used. Lesser horseshoe bats eat a range of
insects, predominantly flies, which they hunt flying low beneath the tree canopy, sometimes
gleaning insects from leaves or branches. 

 

Although lesser horseshoe bats can live for up to 21 years they are particularly vulnerable to human impacts. The requirement for winter and summer roost sites often results in conflicts with property owners seeking to develop old barns or close dangerous mine adits. Modern agricultural practices reduce the number of insects available for the bats to feed on and timber treatments used carelessly in property
maintenance are directly toxic to bats.