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Llanelli Naturalists Newsletter - Summer 1993 - No 55
A.M Hutson and S Mickleburgh

Greater horseshoe bat Rhinolophus ferrumequinum and Lesser horseshoe bat R. hipposideros

Horseshoe bats can be distinguished from all other British bats by the presence of a oomplex horseshoe-shaped nose-leaf. The greater horse¬shoe bat has a head and body length of about 60mm (2W'), a wingspan of about 350mm (14") and a weight of about 22g (less than 1 oz). The lesser horsesnoe bat is one of the smallest British species with a head and body length of about 35mm.(11/4"), a wingspan of about 240mm (9%2") and a weight of about 6g (1/40z). Horseshoe bats are the only British bats that, when roosting, hang free with their wings more or less en folding their body; at rest the lesser horseshoe is about plum- sized, while the greater horseshoe is about pear- sized. Juveniles are greyish in colour, while adults are generally bull brown.

Numbers of both species have declined markedly, partic¬ularly in western and northern Europe, and they are now extremely rare in Britain. The greater is now confined to south-west England and South Wales while the lesser is more widespread, being found throughout Wales and most of western England and western Ireland.

Horseshoe bats begin to emerge from their roost within half an hour of sunset. Between May and August, greater horseshoes return to the roost after the dusk feed and remain there until they leave for a second feed around dawn. From late August they may remain away from the roost all night. Lesser horseshoes often remain active all night throughout the breeding season. They feed amongst deciduous woodland or scrub and perm¬anent pasture, close to suitable roost sites. Greater horseshoes feed mainly on chafers, dung beetles, moths and crane-flies. Lesser horseshoes feed on crane-flies and probably take other small flies and moths.

Both hunt by flying low and fairly slowly, occasionally taking food from the ground. The horseshoe bat's complex nose-leaf is related to the particular type of echolocation system it uses while hunting. Greater horseshoes often like flycatchers, that is, they 'watch' from a regular perch and fly out to take passing insects. They take large prey to a regular feeding perch; insect remains beneath these perches in trees or cave entrances are most evident in spring and autumn.

Breeding

Greater horseshoe bats normally mate' in late September or October, though they may do so later in the winter or even in spring. Mating in lesser horseshoes takes place from late Sept-ember to November or sometimes later. In both species the maternity roosts are occupied from May, though most breeding females do not arrive until June. The usual size of maternity colonies is 50 - 150 for greater horseshoes and 30 - 50 for lesser horseshoes. Initially, adult males are present in these colonies, but they normally depart in mid-July when the young are born. At first, babies are suckled on their mothers' milk, but within four weeks they can fly from the roost and catch insects. Juvenile greater horseshoes are fully weaned at about seven weeks, lesser horseshoes at about 4 - 5 weeks. The breeding horseshoes at about 4 - 5 weeks. The breeding females leave the maternity roost after weaning in September, but juveniles and some immature bats stay until October. Lesser horseshoes are sexually mature within 15 months but greater horseshoes do not reach maturity until their second or third year; one female is known not to  have bred until its tenth year. Female greater horseshoes may not.breed every year. Greater horseshoes have been known to live 25 years in the UK, and 31 years is recorded in France. It is likely that lesser horseshoes will not live quite so long.

Roosts

Summer

Horseshoe bats are traditionally cave dwellers, but very few breed in caves now. Most breeding horseshoes use buildings in the summer months. These tend to be sites where the bats can fly freely into large open roof spaces warmed by the sun, but lesser horseshoes can be found in small attics only accessible by crawling. Some horseshoes, particularly males, use caves and tunnels in the summer. Horseshoes form clusters inside the maternity roost when they need to conserve energy, but will spread out if the roost gets hot. Maternity colonies are sometimes noisy with continuous chattering.   

 

Winter

Horseshoe bats use caves. disused mines. cellars and tunnels as hibernation sites. Greater horse shoes hibernate from late September to mid-May, depending on the weather and food availability. Lesser horseshoe hibernation starts later and ends earlier. Both species feed in winter if suitable mild weather occurs. They awake from hibernation regularly during winter and move ments of 30km (17 miles) or more between hibernation sites are recorded for greater horseshoes in search of suitable temperatures. Hibernation sites are much warmer than those of other bats, the preferred temperature varying between about 11°C in October to 7°C in February though  this varies with age and between the sexes. Greater horseshoes sometimes form clusters in winter sites.

Further Reading

Corbel. G.8 S. Southern. H.N. 1977. The Handbook of British Mammals. Mammal Society/Blackwell Scientific Publications, Oxford. 520pp. £15.00 (3rd Edition expected 1988).

Hutson, A.M. In press. Bats in Houses. Fauna and Flora Preservation Society, !croon. (expected 1987)

Ransome, R. 1980. The Greater Horseshoe Bat. Blandlord Press. Poole. 43pp (out of print).

Richardson. P.W 1985 Bats. Whittet Books. London. 128pp. £5.95.

Schober, W. 1984. The lines 01 Bats. Croom Helm. Kent. 2000P. £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.