Cornwall Mammal Group

The serotine is a large brown bat that occurs
across the south of England. It has been only occasionally recorded in east Cornwall, and then only from bat detector evidence. No roosts have been identified in the county.
This robust bat has dark brown fur on its
back, sometimes with a hint of purple, with a
pale belly. The wings extend to 380 mm and are relatively broad. The triangular ears are twice as long as they are wide and there is a small triangular tragus. The ears and face are dark and there are conspicuously large canine teeth. Serotines are strong and agile flyers and hunt over and around trees for large insects. They will snatch prey from leaves, and may swoop low across grassland or be seen hunting around streetlights.
Their echolocation calls range from 15 to 65 kHz but are strongest at around 28 kHz
when they sound like irregular hand claps. These may be interrupted by occasional
short feeding buzzes as the bat homes in to a beetle or moth.

Serotine bats are perhaps the British bat most dependent on buildings. They roost
high in man-made structures all year round and are therefore highly vulnerable to
disturbance by building work. They show a strong preference for roosting in houses
and churches built in Victorian times, using the easy access to roof spaces and
cavities, and are rarely found in modern buildings.

Serotines hunt for flies and larger moths as well as large beetles such as cockchafers,
usually within 2 km of their roost, although they may travel further to forage. They
emerge from the roost at dusk. The bat’s large teeth are needed to deal with the tough
wing cases of the beetles but have been known to make an impression on careless bat
workers as well.

Maternity roosts,established in May, usually consist of up to 30 individuals, occasionally
more. Males are usually solitary. The single pup is born in early July and weighs about

5g. Most females seem to breed in their first year and possibly every year afterwards but about 30% of the young die in the first week of life and this can be worse in poor weather. Once the young are able to fly at 4 to 5 weeks of age the mothers soon leave the roost and most maternity roosts have dispersed by early September.

The serotine seems to be quite tolerant of colder temperatures and will hibernate in
buildings or near cave entrances. Few hibernating serotines are found - it is thought
that most will find roosting spots in cavities and crevices within the buildings that
they inhabit during the summer.

Serotines, like all bats, are dependant on reliable sources of insect prey and are
therefore vulnerable to changes in agricultural practices which reduce insect numbers. The routine use of cattle-worming drugs together with other changes in cattle management has drastically reduced the numbers of dung-feeding insects on which serotines, and other bats, depend.