Llanelli Naturalists Newsletter - Winter 1992/1993

Serotine bat Eptesicus serotinus

The serotine bat is one of the largest British species with a head and body length of about 70mm (3") and a wingspan of up to 380mm (15"). Serotines weigh about 25g (less than 1 oz). They have long dark-brown fur and are slightly paler underneath. Their face and ears are black.

Serotines are usually one of the first bat species to appear in the evening and can be seen feeding over pasture, parkland, along woodland edges and tail hedgerows, and along roads. They have broad wings and a leisurely, highly manoeuvrable flapping flight with occasional short glides or steep descents. They fly around trees up to a height of 30m, often very close to the vegetation and will even flop. wings outstretched, on to the foliage to catch large insects In open pasture they may fly very low and occasionally take insects from the ground. Early in the year they teed on a variety of flies and moths, but later they teed mainly on larger beetles, such as chafers and dung beetles, and moths. Most of their food is caught within two kilometres of the roost. Serotines are not believed to be particularly migratory, although movements of up to 330km (200 miles) are recorded in Eastern Europe.

Breeding

The maternity colonies, consisting almost ex¬clusively of female bats, start to build up in May. Numbers in the smaller maternity colonies are often very stable from the end of May. A colony usually remains at a single roost site during the breeding season, but some, particularly larger, colonies change roosts frequently. Maternity colonies usually contain between 15 and 30 bats. but there may be as few as eight and occasionally as many as 60. The males probably remain solitary or in small groups, but are occasionally found with females in the spring or autumn. Females normally give birth to their single young in early July, though births as late as mid-August have been recorded. The babies are fed on their mothers' milk and are occasionally carried by their mothers for their first few days. Within three weeks the young are able to make their first flights and within six weeks can forage for themselves. The maternity colony usually disperses by early September, but a few bats remain active at some roosts until early October. Mating normally takes place in September or October. Males and females reach sexual maturity in their first summer. Bats the size of serotines generally live for up to 20 years, although the oldest recorded serotine is six years old.

Roosts

Summer

Serotines roost mainly in buildings, particularly those built around 1900 with a high gable apex and cavity walls. They can be found in much older buildings, but are rarely found in modern buildings. The access to the roost is usually at or near the gable apex or the lower eaves. They roost in crevices around chimneys, in cavity walls, between felt/boarding and tiles/slates, and sometimes in the open roof space at the ridge ends or occasion¬ally elsewhere along the ridge. Droppings are often present in large amounts at the gable ends or around the base of the chimney, although some long established sites show no obvious signs of occupation. The point of access is not well marked, though sometimes it is slightly dis-coloured and there is likely to be a few droppings underneath.

Once the colony has built up, there is often much squeaking before the bats emerge at night. Most of the colony emerges in the first 10 minutes and the total emergence time never exceeds 40 minutes. In the early part of the season the bats return after about 30 minutes and groups of bats will circle around the roost before entering. As the season progresses, more time is spent away from the roost and there may be a secondary peak of activity around dawn. The roost building is sometimes shared with pipistrelle and/or long-eared bats, and serotines have also been known to associate with Natterer's, whis¬kered and noctule bats.

Small numbers of serotines often occur in churches and individuals have been found to usea temporary night-time roost such as a house porch. They are rarely found in trees, which must have provided their natural roost sites.

Winter

Very few serotines are found in winter, but it is likely that most hibernate in buildings. It is possible that at least part of the summer colony may remain at the same site for some, if not all, of the winter period. They have been found inside cavity walls and disused chimneys. Very rarely, they have been found hibernating in the coldest parts of caves, either in roof crevices or in accumulations of boulders.

Further Reading

Corbel. G.B. 8 Southern. H.N 1977. The Handbook of British Mammals. Mammal Society/Blackwell Scientific Publications. Oxford. 520pp. (3rd Edition expected 1988).

Hutson, AM. In press. Bats io Houses. Fauna and Flora Preservation Society. London. (expected 1987). Richardson. P.W. 1985. Bate. Whittet Books, London. 128pp £5.95

Schober, W. 1984 The line of Bats. Groom Helm. Kent. 200ppe £13.95.

Stebbings, R.E 1986. Bats. Anthony Nelson, Shropshire (Mammal Society Series). 32pp. £2.50

Bats and the Law

Bats and their roosts are protected under the Wildlife and Countryside Act 1981. Should any work be planned that may disturb bats or their roost, the Nature Conservancy Council must be consulted. Local bat groups will also be happy to give help or advice.