Warwickshire Bat Group

Greater Horseshoe

The Horseshoe bats can be distinguished from other British bats by the presence of a complex horseshoe-shaped noseleaf, which is related to their 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.

When roosting they hang free with the wings more or less enfolding their body. An advantage when it comes to recording them as they do not hide in crevices making them easier to spot. The Greater Horseshoe bat is one of our largest species - the size of a small pear.

The Greater Horseshoe bat has shown a marked decline, particularly in western Europe. It is rare in Britain and now confined to south-west England and South Wales. It is estimated that the number of Greater Horseshoe bats has declined by 98% in the last 100 years. The British population is thought to number only between 4,000 and 6,000 individuals.

The decline of the Greater Horseshoe bat may due to the factors such as disturbance of roosts and intensive agricultural practices including loss of permanent pasture. They are particularly sensitive to disturbance at 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 also important. The use of pesticides has led to a decrease in availability of larger beetles, particularly cockchafers, and moths over large areas of the countryside.

Download a pdf copy of "Managing Landscapes for the Greater Horseshoe Bat" by English Nature (228Kb).

Research by Stephen Rossiter of the University of Bristol, Roger Ransome and colleagues (Proceedings of the Royal Society of London B, vol 268 pp1053-60) has suggested that the overwinter survival rates of males is related to their degree of inbreeding - less inbred individuals were more likely to survive their 1st and 2nd winters. The researchers conclude that inbred bats may have weaker immune systems and are, therefore, less able to withstand disease. These results mean that it is very important to protect the mating sites where pairings occur between bats from different colonies.

In 2003 English Nature commissioned a study to radio-track Greater Horseshoe bats in Dartmoor. They found that they did not forage much within woodland but preferred a mixture of habitats. These included tree-lined watercourses, tall bushy hedges, and tree-lines around grassland or scrub. The adult bats were happy to commute 6km to these feeding areas but the juveniles stayed within 4km of the roost. Also the research showed that an enclosed corridor of vegetation outside the roost is important as it allow them to emerge safely before it gets totally dark.

flight & ultrasound

Greater Horseshoe bats emerge from their roosts within half an hour of sunset. Between May and August they usually return to their roost after about an hour and remain there until their second feed around dawn. However, from late August they may remain away all night. They require a mosaic of woodland and pasture to ensure an adequate food supply whatever the weather conditions. For example, during a chilly Spring evening woodland is better while in the warmth of summer nights pasture provides a bountiful supply of moths and beetles.

Insects are taken in flight or occasionally from the ground. Greater Horseshoe bats often behave like flycatchers, 'watching' from a regular perch and flying out to take passing insects. Large prey is taken to a regular feeding perch; insect remains beneath such perches in trees, porches or cave entrances are most evident spring or autumn. Greater Horseshoe bats feed mainly by low-flying hunting.

Greater Horseshoe bats have an almost constant frequency call of about 82 kHz. On a heterodyne bat detector a series of continuous warbles can be heard. It is just as well that we cannot hear their calls as at a distance of 10cm they are comparable to the energy of a jet aeroplane! (27 Newtons per square metre).

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.

  Greater Horseshoe recorded on a Heterodyne bat detector

breeding

In the autumn males form separate colonies where oestrous females visit them to mate. Mating can also take place in late winter or even in spring.

Maternity colonies begin to gather in May and reach peak numbers in mid-June to July when most breeding females return. Males up to 14 years old return with breeding females in June, but most leave when the young are born in mid-July.

Birth often occurs at dusk. The female hangs from her feet and the single baby emerges into the overlapped wings. Shortly afterwards the young is left in the roost while the mother flies off to feed. The young can open their eyes at nine days of age. At first the young feed on their mother's milk, but after about 5 weeks can fly and start to catch insects. They are fully weaned at 7 weeks when the adults usually leave the colony but juveniles and some immature bats may stay until October or even later.

Females Greater Horseshoe bats are not usually sexually mature until their third year and one female did not breed until her tenth year. They may not breed every year. Males are usually sexually mature by their second or third year.

summer roosts

Greater Horseshoe bats were originally cave dwellers but few now use caves in summer as they are now too few bats of this species to generate the amount of body heat to successfully raise their young. So, most breeding females use buildings which are warmed by the sun. They choose sites with large entrance holes with access to open roof spaces as, like the Lesser Horseshoe, they prefer to fly directly into a roost site. Such sites are normally in larger, older houses, churches and barns. A range of other sites are used in Spring, and males hold territory at mating roosts in autumn.

These bats form clusters inside maternity roosts to keep warm but will spread out if the roost gets too hot. Maternity colonies can be noisy with continuous chattering, chirping and scolding calls. Males also use caves and tunnels in the summer and even the breeding females appear to need a nearby cave or tunnel to retreat to when bad weather affects their food supply.

Winter Roosts

The Greater Horseshoe bat uses caves, disused mines , cellars and tunnels as hibernation sites. These sites can be up to 50 km from the breeding roost. They may hibernate from late September to mid-May, depending on the weather and food availability. They awake from hibernation at frequent intervals and, in their search for suitable temperatures, movements of 30 km between sites are often recorded. They will feed in winter during mild weather.

Hibernation sites are much warmer than those of many other bats with temperatures varying from about 11ºC in October to about 7ºC in February, although this varies with age, sex and body condition. They will sometimes form clusters in winter sites although adult females are more solitary.

Generally, female Greater Horseshoe bats are found deep within the hibernaculum and move little throughout the winter. Females are usually much fatter and can afford to find a relatively warm place to hibernate. The males however often keep nearer to the entrance and frequently move site. Immature Greater Horseshoe bats are highly gregarious at all times and can form groups with adult males of up to 300 in winter.

Description
Head and Body Length	57 - 71 mm
Forearm Length	54 - 61 mm
Wingspan	350 - 400 mm
Weight	17 - 34 g
Colour	Adults buff-brown; juveniles greyish.
Life Cycle
Mating Period	Late September - October
Maternity Colonies	Late spring. Young: usually 1 born mid-July, weaned within 7 weeks.
Colony Size	50 - 200 (rarely 600)
Longevity	Up to 30 years.
UK Status	Endangered.
Habitat and Food
Summer Roosts	Mainly buildings.
Winter Roosts	Caves, disused mines, cellars, tunnels.
Feeding Habitat	Deciduous woodland, scrub, permanent pasture, water, along hedgerows.
Food	Chafers and dung beetles, noctuid moths, crane-flies, caddisflies.

further reading

Dietz C, Dietz I and Siemers BM: Wing measurement variations in the five European horseshoe bat species (Chiroptera: Rhinolophidae). Journal of Mammalogy, (2006).

Dietz C, Dietz I and Siemers BM: Growth of horseshoe bats (Chiroptera: Rhinolophidae) in temperate continental conditions and the influence of climate. Mammalian Biology, (2006).

Dietz C, Dietz I, Ivanova T and Siemers BM: Movements of horseshoe bats (Rhinolophus, Chiroptera: Rhinolophidae) in Northern Bulgaria. Myotis, (2006).