UPDATE
The law protecting bats has changed and the legal references in this booklet are now out of date. Now, before starting any works in a dwelling-house which may disturb bats or a bat roost, such as building work or remedial timber treatment, or which may damage, destroy or obstruct access to a bat roost, you must be licensed by the Scottish Executive. Please contact your local SNH office for further advice or refer to the Conservation (Natural Habitats, &c.) Amendment (Scotland) Regulations 2007 which you can see online at http://www.opsi.gov.uk/legislation/scotland/ssi2007/20070080.htm

What's special about bats?

Bats are highly specialised and remarkable animals with some amazing features. They are the only true flying mammals. Like us, bats are warm-blooded, give birth, and suckle their young. They are also long-lived, intelligent, and have complex social lives. Although they're often called flying mice, bats are not closely related to mice but form a special group of their own: the Chiroptera.

World-wide, there are almost 1000 different species of bat, ranging from the tropical flying fox, with a wing-span of almost 2 metres (6'), down to the hog-nosed bat of south-east Asia, which is little bigger than a large bumble-bee. In Britain there are 16 species of bats, nine or ten of which occur in Scotland.

In many parts of the world, including Britain, the number of bats has declined significantly in recent years - some species have declined to the point of extinction. Although we don't have much historical information, it's clear that many of our bats are under threat and some species are now much less common than in the past.

Wings

Bats' wings are made out of a soft, elastic membrane of skin stretched over their arms and legs and which continues to meet the tail. Bats have the same bones in their arms as humans but their hand bones are much longer and support their wings; the group's name comes from the Greek for hand (chiro) and wing (ptera). The structure of bats' legs enables them to hang upside down whilst roosting without needing any energy to hold on, although many bats prefer to roost in small holes and crevices.

Sonar

Although bats certainly aren't blind, their sight is not used for hunting insects in the dark. They have developed a highly sophisticated echolocation system that allows them to catch tiny insects and avoid obstacles, even in complete darkness. When they're flying, bats produce a stream of high-pitched squeaks and listen to the echoes to produce a sound picture of their surroundings.

It was only discovered in 1793 that bats could avoid obstacles in the dark, and only 50 years ago that their echolocation system was detected. Bat squeaks are too high-pitched for humans to hear, so many bat-enthusiasts use electronic bat-detectors that pick up these high-pitched squeaks and turn them into audible sounds that can be used to identify different species in the field.

Feeding

Different species of bats around the world feed on a variety of foods including fruit, nectar, small mammals, fish and frogs, but Scottish bats eat only insects which they catch in flight or pick off water, the ground or foliage. Some specialise in catching large insects such as beetles or moths while others eat thousands of very small insects, such as small moths and the ubiquitous biting midge, a single bat may consume over 3000 of these in a night. Bats feed where there are lots of insects, so their favourite feeding areas include traditional pasture, woodland, marshes, ponds, and slow moving rivers. Typically, bats will feed for two or three hours around dusk and dawn when insects are most active.

Hibernation

There are very few insects around in winter, so animals that eat insects have to adopt different strategies in order to survive. Birds migrate south to warmer climates, but our bats have evolved a different technique - hibernation. During the autumn, bats put on weight. Then as the weather gets colder, they let their body temperature drop to close to that of their surroundings and slow their heart rate to only a few beats per minute. By entering this state known as torpor, bats can make their food reserves last much longer.

Surprisingly, bats don't sleep right through the winter; they may wake up and go out to feed and drink on mild evenings when some insects are found. Even on very cold nights, bats may be seen on the wing as they move to more sheltered roosts. Flying in the winter uses up energy that bats can't easily replace and so their chances of surviving the winter might be affected if they are disturbed while hibernating. In Scotland, bats are spotted so rarely in winter that it has been suggested that they migrate in the same way as many birds do (and some bats in continental Europe).

Bats have good control over their body temperature. Even during the summer, bats can enter torpor during cool spells. This helps them to conserve energy and to survive periods of bad weather when food is scarce.

Breeding

Our bats have a unique and fascinating way of combining their breeding cycle with hibernation. Mating takes place during the autumn. The female stores the sperm in her body throughout the winter and only becomes pregnant the following spring. Pregnancy lasts between six and nine weeks and can vary in length depending on the weather. Usually bats have only one baby each year and it is looked after very carefully. The baby bat lives on its mother's milk for four to five weeks until it can fly and hunt for itself. A mother may fly to another roost site and carry her baby with her. Bats don't bring food back to the roost to feed their young.

Life span

Compared with other small mammals such as shrews and mice, which often live for less than a year, bats are amazingly long-lived. They can live over 25 years in the wild - a remarkable feat for an animal weighing less than 10 grams! Perhaps this is because they spend more than half their lives asleep.

Bats and their roosts

A bat's choice of roost depends upon, amongst other things, its species and sex, the time of the year and the availability of food. In any one year several different roosts are used on a seasonal basis, where conditions meet the bats' social and reproductive requirements at the time. As bats cannot always rouse themselves quickly to escape from danger the roost must be safe and free from disturbance. Summer roosts are generally close to good feeding habitats which are rich in insects.

Most bats form social groups for at least part of the year and it is at these times that bat roosts are most obvious.

Adult females gather together in maternity roosts in late May to early June to give birth and rear their babies. As soon as the young start to fly these maternity colonies begin to break up and the bats move to other roosts. Bats may congregate from a large area to form these colonies, so any major disruption at this summer breeding site could potentially wipe out all the females from this area. In contrast, male bats typically prefer to live alone or in small groups in cooler sites. This may be another adaptation to help them save energy. During late summer male bats set up territories around a mating roost to which they attract females.

Although bats can be found in all sorts of places, there are three main types of roost: Buildings such as houses, churches, farms, bridges, ancient monuments, fortifications, schools, hospitals and all sorts of industrial buildings. These are most important in summer, though some are used throughout the year. Caves, mines and other underground places like cellars, ice-houses and tunnels. These are most important for hibernation as they give the cool, sheltered and stable conditions that bats need during winter. Tree holes - these are used by bats throughout the year.

Some favour buildings throughout the year while others rely on buildings during the summer and caves or abandoned mines during the winter, and yet others prefer tree holes. Bats have well established traditions and tend to return to the same sites, at the same time, year after year.

If bats are present during the summer, it's often possible to see them fly out at dusk or even hear them inside the roost on hot days or before they emerge in the evening. Frequently, though, only signs of bats will be seen rather than the animals themselves. The most characteristic signs are their droppings which are composed of the indigestible remains of their insect prey. These are roughly the size and shape of mouse droppings but they crumble to a powder when dry and are usually found stuck to walls or in small piles below roosting bats or below the roost exit.

Because bats come back to the same roost year after year, their roost is legally protected even when the bats are not there.