Greater horseshoe bats may leave evidence of their presence even when they are away from the roost. They are particularly fond of dismembering moths and beetles near the entrance to the roost, leaving a tell-tale scattering of wings and wing
cases. The droppings are large, up to 13 mm long, and vary in colour and texture according to the diet. Like all bat droppings they crumble to dust very easily, unlike rodent droppings which tend to be hard when dry.
Colonies of greater horseshoe bats are scattered across Cornwall, mainly in less exposed areas, but there are only 4 known breeding roosts. Many of the hibernation sites are associated with old mine workings. The UK is at the northern limit of the greater horseshoe’s
range and it occurs from the Mediterranean to the far east.
Monitoring of summer maternity and hibernation roosts by licensed bat workers. Mist net trapping by licensed bat workers. Emergence surveys. Bat detector monitoring. Cat kills and incidental reports.
One of our largest bats (weighing up to
34 g, with a wingspan of 40 cm), and also one of our rarest, the greater horseshoe
bat has an elaborate nose-leaf which is critical to their particular system of echolocation. Whereas most British bats emit their echolocation sounds from the mouth, horseshoe bats use the nose.
The tablespoon-sized body is covered in buff-brown fur above and below and when the bats are roosting they hang upside down and wrap their wings around their bodies. They are conspicuously larger than the only other British bat to roost in this fashion, the lesser horseshoe.
During the summer greater horseshoes emerge from their roosts soon after sunset and hunt close to the ground. As with the majority of British bats,
they are most readily identified with the use of a bat detector. Greater
horseshoe bats use long constant frequency echolocation calls at about 82 kHz which is picked up on a heterodyne bat detector as a continuous warbling.
Greater horseshoe bats hunt low over old pasture, parkland, woodland and scrub. Their summer roosts are often in old buildings. In Cornwall they use some of the old mine shafts and adits, where they can fly directly to the roost site.
The bats mate in autumn but fertilisation only takes place in the spring. Female bats assemble at maternity roosts of up to 600 bats from April onwards. The bats require sites that provide warmth and space and are free from disturbance. Births occur from late June to July with the blind and almost naked pups weighing only about 6 g at birth. Pups are left clustered together whilst the mothers leave the roost to hunt, each searching out their own pup to suckle them on their return. Pups are weaned at about 7 weeks, after which the mothers leave the roost, although the youngsters remain there until October before moving to hibernation sites.
Greater horseshoe bats breed at 2 or 3 years of age. During the summer males are usually solitary, but occupy traditional mating roosts in the autumn where they may mate with the same group of females over many years, leading to strong genetic connections within colonies.
Winter hibernation roosts are often close to the summer roosts, although bats have been recorded travelling over 100 km from their summer sites. The roosts are relatively warm, about 11ºC, in old mines, caves, or unheated cellars and tunnels. Males often wake up and feed, or even move to different roosts, during mild spells.
The bats feed up to 12 km from their roosts, although usually within 4 km, flying low to hunt for larger moths and beetles such as cockchafers and dung beetles and even picking them off the ground. They may also scan for prey while hanging from a convenient branch. Loss of roost sites and the impact of changing agricultural practice on their insect prey are probably responsible for falling numbers.
Did you know?:
When roosting, the bat’s weight locks its claws to grip; to release itself the bat must first flex its knees. Greater horseshoe bats living further south have their maternity roosts in caves,
in the UK they often need to use the sun’s heat in the roofs of old buildings to keep warm enough.
Greater horseshoe bats, their roosts and hibernation sites, are the subject of extensive legal protection, specifically the Wildlife & Countryside Act 1981 and the European Habitats Directive. This bat is threatened with extinction across northern Europe and has declined dramatically across central Europe. Numbers in the UK are barely a tenth of what they were 100 years ago, although the population is thought to be stable and possibly increasing this is still less than 5000 individuals in the whole country. The greater horseshoe bat is a UK BAP priority species and classified as endangered. Agri-environment schemes are targeted to improve feeding areas for the bats by reducing pesticide use and encouraging sympathetic land management. Roosts are particularly threatened by development of old barns and houses, and the closure of old mine shafts for safety reasons.
Bats are often difficult to see, but the greater horseshoe bats at Pentire Head in North Cornwall are a regular attraction for visitors to the National Trust bat events on this beautiful headland. On warm summer evenings 60 or more female bats emerge from
their maternity roost in the old
drainage adits of an abandoned medieval lead and silver mine and swoop low across the clifftop
meadows in search of insects, often
passing within inches of spectators.
© David Chapman