Echolocation
Calls range from about 25 to 50 kHz, with the peak frequency at around 25 to 27 kHz, or higher when close to the ground. Calls sound like ‘smacks’ on a bat detector. The repetition rate is very irregular, and can be confused with noctules or Leisler’s in certain environments.
Habits
Parkland, pasture and woodland edge are important foraging sites for this species, especially where cattle graze. In spring it feeds on flies and moths but in summer chafers and dung beetles are an important part of its diet.
It relies heavily on buildings for roosting in summer, in disused chimneys, under ridge tiles, inside cavity walls and other small crevices. Access points to the roost are generally high up at about six to eight metres above the ground. Most roosts are in older buildings from around 1900. Very few serotines are found in winter; only occasionally have they been recorded in caves, and it is likely they hibernate in buildings.
Reproduction and life cycle
Reproductive females usually remain at a single roost during the summer, but other roosts nearby may also be used by non-breeding females. Almost nothing is known of the mating behaviour.
Distribution, status and conservation
One of our less common species, monitoring data collected as part of the National Bat Monitoring Programme (NBMP) indicates potential long-term decline, especially in south-east England. There is also some suggestion of regional differences, with this species faring better in the south west than in the east. Loss of both feeding habitat where large insects can be found, and of buildings for roosting, have made it vulnerable.
In Kent the decline has given cause for concern for over a decade. A number of summer roosts holding these bats over the last 20 years appear not to have been used recently. Numbers at roosts monitored each summer have declined, some to single figures. One roost in east Kent has been monitored since 1986, when 62 adults were counted out; in 2012 only 23 adults emerged. More recent monitoring shows continuing losses and further roost abandonment.
The conservation of serotines depends on the effective management and protection of the farmed landscape around maternity roosts and other sites used by bats. Permanent grazing pasture is crucial.
