Bats are the second largest mammalian group after rodents, representing about 20% of all mammalian species. Regardless of their association with Halloween and the supernatural, bats are a remarkable group of animals. The only truly flying mammal, a life span exceptional for their size, complex social interactions, echolocation of their prey and a metabolism capable of sustaining flight and entering torpor to conserve energy.
Truly remarkable animals
All bats belong to the order Chiroptera, meaning 'hand-wing' - the bat’s wing is comprised of a membrane of skin stretched from the foot across the extended tips of the fingers. Bats are divided into two sub-order; megachiroptera, comprising fruit bats and flying foxes, and microchiroptera which includes all other species. All UK bats are microchiroptera.
In the UK there are 18 species of bats, 17 of which breed here - this represents almost a quarter of our mammal species. The number of species found is greatest in the south and west and gradually reduces further north and east, so that in Scotland there are just nine species, with just tiny pipistrelle bats making it as far north as the Orkneys.
What do bats eat?
All UK bats are insectivorous, although each species has its feeding preferences, from gnats to moths, and hunting techniques and adaptations to match. Whilst the broad wings and often almost hovering flight of lesser horseshoe bats is adapted to hunting among the cluttered vegetation of scrub and woodland edge, Daubentons bats have specially adapted large feet for ‘trawling’ insects by flying close to the surface of still water.
Flying uses a lot of energy. The tiny pipistrelle can eat over 3,000 insects in one night including mayflies, lacewings, small moths, midges, caddis flies and mosquitoes.
Are bats blind?
Despite the saying 'blind-as-a-bat', bats have quite good sight. Bats may use their vision for locating roosts or for spotting predators. Nonetheless echolocation is what bats are known for and provides a way in which they are able to navigate in the dark and to locate prey.
Echolocation is achieved by producing an ultrasonic pulse emitted through the bat’s mouth or the nose which is reflected back from any object it strikes. The timing and frequency with which the signal returns allows the bat to identify the distance and any movement in the object with great accuracy, and to distinguish between an insect and the surrounding vegetation.
The exact frequency and pattern of the echolocation is adapted to the prey of each bat species and the habitat within which they hunt. Bats which feed on small prey in cluttered habitats tend to have a higher frequency emission than those which hunt larger prey over more open habitats. The frequency of the echolocation is a key to identification using a bat detector which is able to pick up the ultrasonic emissions.
Do bats hibernate?
In winter bats hibernate, entering a state of torpor to conserve energy and reducing their heart rate to as low as four beats per minute - which is incredible considering that in-flight the oxygen demand may mean that their heart rate reaches over 1000 beats per minute.
Winter hibernation roosts need to have a constant low temperature, but free from frost, and damp to prevent the animals desiccating. Caves and old mine shafts often provide the conditions for many bats species to over-winter.
Bats enter hibernation during October and may not fully leave the hibernation roost until mid-May, although they may regularly arouse from torpor during hibernation when conditions are suitable for them to feed.
Where do bats live?
In the summer months, bat roosts are normally in buildings, trees holes and under bridges and similar structures. Bats will also use artificial bats boxes where there is a shortage of tree holes or other crevices in old trees. Bats may make use a number of different roosts over the summer, including night roosts where they rest to digest food before resuming hunting.
The presence of bats is a good indicator of the health of the woodland environment, demonstrating the presence of a number of ‘trophic’ levels – tiers in the food chain including plants and insects as well as the higher insect feeders. Equally, woodland with old trees providing niches for roosting, well-structured woodland edge with shrubs and insect life and vigorous hedges, riparian woodland, field and hedgerow trees connecting woodland are all important to the survival of many bat species.
Many species of bats depend on trees and woodland – to provide roosts and hibernation sites (around three quarters of British bat species use trees for roosts), for feeding and as a way of navigating around the landscape. Two species in particular – Bechstein’s bats and Barbastelle bats have a strong association with broadleaved woodland.
How do bats hang upside down?
The ability of bats to hang upside down is made possible by a locking mechanism in their feet which is triggered by the weight of the bat pulling on a tendon which locks by friction to a surrounding sheath. In this position the bat is capable of suspension even during torpor. As the bat flies off, the weight is relieved from the tendon and it unlocks, releasing the grip.
Most bats are capable of crawling after landing on a surface and so can secrete themselves in nooks and crannies. The two species of horseshoe bats however are unable to crawl and so must fly and turn upside down, hanging free hand from the roost in open view.
How long do bats live for?
Bats are very long lived compared to other mammals of a similar size. Many species live for more than 30 years and a ringed Brandt’s bat has been recorded at 41 years old, remarkable when they only weigh 5-7 grams. This compares to just one to three years for most small rodents.