Lesser Horseshoe

The Lesser Horseshoe is one of our smallest British species. At rest it hangs with the wings wrapped around the body and is about the size of a plum. Like the Greater Horseshoe bat, it has a complex noseleaf which is related to its particular type of echolocation system. Instead of using their larynx to produce sonar they use their nose and emit a 90 degree cone of ultrasound through their noseleaves.

Like the Greater Horseshoe bat, this species has shown a marked decline in numbers and distribution particularly in western and northern Europe although there is evidence of a recent increase in some areas. The Lesser Horseshoe bat is rare in the British Isles and is confined mainly to Wales, western England and western Ireland.

Lesser Horseshoe UK distribution However there is some good news - the BCT's NBMP (National Bat Monitoring Programme) reported in January 2001 that Welsh populations have increased by a rate of 6.2% per annum in the years 1993 to 1999. Overall the UK population has risen by 4.8% over the same period, but the English population may be increasing very slowly or even declining. It is thought that their success in Wales is due to the preservation of hedgerows and other wildlife corridors, the amount of traditional pasture available and less intensive farming practices.

Lesser Horseshoe hanging The decline of the Lesser Horseshoe bat is attributable to several factors including disturbance to roosts and intensive agricultural practices. Lesser Horseshoe bats are particularly sensitive to disturbance especially of their nursery and winter roosts. These sites need to be specifically protected and entrance holes left unobstructed. The conservation of their feeding habitats and food sources is of paramount importance. The use of pesticides has probably led to a decrease in their available food source.

flight & ultrasound

Lesser Horsheshoe flight path

In the summer months Lesser Horseshoe bats emerge about half an hour after sunset as it is getting quite dark The emergence follows a period when the bats fly around within the roost with some appearance outside the roost entrance; presumably they are testing the conditions outside before emergence. Although there are peaks of activity at dusk (and also at dawn) bats are active all night throughout the breeding season. Lesser Horseshoe bats are sensitive to disturbance and twist their bodies as they scan their surroundings before flying off.

Lesser Horsheshoe Lesser Horseshoe bats feed amongst vegetation in sheltered lowland valleys. They fly close to the ground, rarely more than 5m high, with frequent circling over favoured areas and often 'gleaning' their prey off stones and branches. Large prey is often taken back to a temporary night roost or sometimes dealt with whilst hanging in trees. Feeding remains are found in such places, particularly in porches and the entrance to tunnels.

Lesser Horseshoe bats have an almost constant frequency call at about 110kHz. On a heterodyne bat detector a series of continuous 'warbles' can be heard.

Horseshoe bats rely on the apparent change in frequency caused by the relative movement of a sound source and receiver. This change called Doppler shift, is the same phenomenon that appears to make the pitch of the siren on an approaching police car grow higher as it approaches and then deepen as it passes by. The Horseshoe bats compare the pitch that they emit from their noses to that which returns to their ears. In this way they can distinguish a stationary tree from a flying insect. So they are very insensitive to the emitted frequency and exceptionally sensitive to frequencies just above and below it.

Lesser Horseshoe call on a Heterodyne bat detector

breeding

Lesser Horseshoe head Mating takes place during autumn, sometimes later. maternity roosts are almost always formed in buildngs and may be occupied from April, though most breeding females do not arrive until May.

Maternity colonies of the Lesser Horseshoe bat are of mixed sex, with up to a fifth of the colony being male. Approximately half to two-thirds of the females in the nursery roost give birth to a single young between mid-June and mid-July.

Lactation probably lasts four to five weeks, by which time the young can fly from the roost. They are completely independent at six weeks and nurseries disperse between August and October (occasionally November). Most young are sexually mature in their second autumn.

summer roosts

Lesser Horseshoes in roof space Lesser Horseshoe bats were originally cave dwellers but summer colonies are now usually found in the roofs of larger rural houses and stable blocks offering a range of roof spaces and a nearby cellar, cave or tunnel where the bats can go torpid in inclement weather. They prefer access through an opening that allows uninterrupted flight to the roof apex but they are capable of using more inconspicuous gaps. The colony may shift between attics, cellars and chimneys throughout the summer depending on the weather. The whole colony may form a dense cluster, especially in cooler weather during lactation but if the roost gets very hot they hang spaced slightly apart.

winter roosts

The Lesser Horseshoe bat uses caves, mines, tunnels and cellars as hibernation sites. They hibernate from September or October until April and frequently into May. Lesser Horseshoe bats are often active in the hibernacula in autumn and spring especially towards dusk in warm weather when feeding is more likely to be successful. They appear to select places with similar temperatures to Greater Horseshoe bats, preferring temperatures of up to 11ºC and with a high humidity.

Males tend to arrive earlier than females and are often more numerous. Many sites only have one or a few bats hibernating in them and it is rare to find large number in a site. Even when aggregated, Lesser Horseshoe bats do not cluster but hang a little apart from their neighbours, usually exposed but sometimes in open crevices. They may be found from almost ground level to over 20m and venture much further into underground sites than other bats.

Description
Head and Body Length	35 - 45 mm
Forearm Length	35 - 42 mm
Wingspan	200 - 250 mm
Weight	5 - 9 g
Colour	Adults pinky buff-brown, juveniles greyish (until first summer after birth).


Life Cycle
Mating Period	September to November.
Maternity Colonies	Established late spring. Young: 1 born mid-June to mid-July, weaned at 6 weeks.
Colony Size	30 to 70 bats (occasionally 400).
Longevity	Up to 21 years.
UK Status	Endangered.


Habitat and Food
Summer Roosts	Originally cave dwellers, now roofs of larger houses and stable blocks.
Winter Roosts	Caves, mines, tunnels, cellars.
Feeding Habitat	Open deciduous woodland, scrub, parkland, wetland and permanent pasture.
Food	Flies (mainly midges), small moths, caddisflies, lacewings, beetles, small wasps, spiders.

Lesser Horseshoe

flight & ultrasound

breeding

summer roosts

winter roosts

further reading