What are bats?
Bats are the only true flying mammal and belong to the order Chiroptera
How many species of UK bats are there?
There are 17 breeding species of bats in the UK. An additional species, greater mouse-eared bat, is represented by one known individual that has been turning up at the same hibernation site in Sussex virtually every year since 2002.
We don’t know whether it spends the whole year in the UK or whether it spends the summer in mainland Europe where this species is more widespread. A few other species turn up as occasional visitors but with climate change it seems likely that at least one or two of these might become resident breeding species in the UK. The species most commonly encountered are common pipistrelle and soprano pipistrelle, but most parts of the UK will have a range of different species.
What is a group of bats called?
A “colony” of bats is used for a large grouping of roosting bats. One colony may be spread across several roosts. A large number of bats in flight is known as a “cloud” of bats.
How do bats fly?
There are a few other mammals that can glide from tree to tree, for example flying squirrels, but bats are the only mammals with true flight.
Their wings are formed from modified hands with elongated fingers which have a wing membrane stretched across them (bats comprise an order of mammals called Chiroptera which means hand-wing). This gives them extremely manoeuvrable flight. The thumbs are not part of the wing and are kept free for grooming and hanging the right way up (from a human perspective!).
Why are bats protected?
Bats are protected due to evidence of long-term declines, both in terms of numbers and the range of some species, with the biggest changes thought to have occurred over the last 100 years. According to the UK IUCN red list, four of the 11 mammal species native to Britain classified as being at imminent risk of extinction are bats.
Bats are still under threat from building and development work that affects roosts, loss of habitat, the severing of commuting routes by roads and threats in the home including cat attacks, flypaper and some chemical treatments of building materials. Without legal protection we would almost certainly see the decline of more bat species.
Do bats have any predators?
Natural predators include owls and birds of prey, the latter probably increasingly so as light pollution enables them to hunt after dark. However, the biggest killer of bats is the domestic cat - here are some tips for stopping your cat hunting wildlife
Do bats carry disease?
Globally, bats are considered natural hosts of a number of viruses, most of which are not harmful and cannot be passed to humans. Bats don’t host any more disease-causing viruses than any other groups of animals (mammals and birds) of similar species diversity.
Do British bats carry rabies?
The only known zoonotic disease (disease that can impact human health) associated with bats in the UK is rabies caused by European Bat Lyssaviruses (EBLV). There are two known types: EBLV1 and EBLV2. These are not the classical rabies virus, which has never been found in a bat in Europe. EBLVs have only been found in a small number of bats in the UK. There is no risk if you do not handle bats.
Are bats blind?
No, bats are not blind and in fact have good vision. The myth that bats are blind probably came about because many species use sound to navigate around their environment at night, a system known as echolocation. While they use their night vision to get a general impression of their surroundings, they need to use echolocation to pick out finer details including their insect prey.
What is echolocation and how do bats use it?
Echolocation involves shouting very high-pitched (ultrasonic) sounds several times per second and listening to the echoes bouncing off objects around them. This enables them to form a very detailed “sound picture” of their surroundings. They can identify the distance to an object, its size and details, what type of object it is and whether it is moving (e.g. an insect in flight). With their echolocation, horseshoe bats can even identify different species of flying insect based on the speed of the insect’s wingbeats.
Where do bats live?
Bats are incredibly diverse, each species is unique so it’s difficult to make generalisations. Around the world, bats use a wide range of different roosts from carnivorous pitcher plants to hibernating in snow. In the UK, roosts will typically be in trees, buildings, other built structures such bridges and tunnels, and caves and mines.
They will use different types of roosts at different times of year. In the summer, breeding female bats gather together in warm roosts as this will help development of babies in the womb and after they are born. At this time of year male bats tend to roost on their own or in small groups, with a less specific need for warmer roosting locations.
In the winter, when there are few invertebrates for bats to feed on, they move to sites with a cool, stable temperature and high humidity, where they can go into long periods of torpor. This enables them to avoid burning off the fat reserves they have built up before going into hibernation.
How long do bats live?
Relatively speaking, bats are long-lived for mammals of their size. Some can live more than 30 years and the record is 41 years for a Brandt’s bat. This is thought to be partly due to their nocturnal habitats keeping them relatively safe from predators and could also be linked to hibernating for part of the year.
Probably most importantly, bats seem able to avoid many of the ageing processes that other mammals are subject to, and it is thought that studying the reasons behind this could help humans achieve healthier old age.
How do bats reproduce?
Bats usually mate in the autumn but implantation is delayed until the spring. Around April/May time, female bats start to form large maternity colonies within roosts that have the required degree of warmth. In the UK bats typically only have one baby in a year, though occasionally twins are born. Bat babies are known as “pups”.
Birth typically occurs in June. As bats are mammals, they give birth to live young, which at birth are typically 20-30 per cent of the mother’s weight. Bats can give birth while hanging upside down but more typically they will be in a head-up or horizontal position, using their wings and tail membrane to cradle the pup. The pups are suckled by their mothers for four to five weeks until they are old enough to fly. They then begin to venture out from the roost to forage for food.
What do bats eat?
Globally, different species of bat have evolved to eat a wide variety of foods, including nectar, pollen, fruit, invertebrates, blood (the three species of vampire bat found in South and Central America), frogs, fish, birds, scorpions and other bats! All the species found in the UK feed mainly on insects but a few other types of invertebrates, such as spiders, can be included in their diets.
When do bats hibernate and for how long?
Bats begin preparing for hibernation in the autumn, foraging closer to their hibernation sites and depositing large reserves of fat in their bodies, either through increased feeding or going into torpor after feeding.
Torpor is a controlled reduction of body temperature and slowing down of breathing rate, heart rate and metabolic rate. This enables bats to survive cold weather when there are few insects to feed on, relying on their stored fat reserves for their survival. The onset of cold weather will prompt them to start spending longer periods of torpor within their hibernation sites.
Typically this occurs from November to March but bats will arouse from torpor periodically throughout the winter to drink, forage (during milder spells) or change location (within the site or to another site) in response to changes in temperature. Bat hibernation sites typically have a cool, fairly consistent temperature, high humidity and low levels of disturbance. They include tunnels, caves, mines, cellars, outbuildings and trees.
Why do bats hang upside down?
One major reason why bats hang upside down is that their forelimbs have a completely different specialisation: they are wings for flying! Bats can hang the right way up by their thumbs (for example, when giving birth) but it is their feet that are specialised for hanging. The weight of the bat pulls the toes tightly shut meaning that the bat expends no energy in gripping on and can sleep in this position. It will take a small amount of exertion to open the toes in order to let go. Hanging upside down at height gives the advantage of being relatively safe from predators and, in the event of any danger, quickly launching into flight to escape.
What do bats sound like?
It depends on the species but as described earlier, bat echolocation is largely ultrasonic, meaning that most of these sounds are beyond our hearing range. However, we can convert their echolocation calls to our hearing range using a heterodyne bat detector, which enables us to hear the sounds in real time but converted to distinctive smacks, clicks, chips, chops and warbles, depending on the species.
With other types of bat detector we can make recordings of bat calls and slow them down which makes them sound like chirps, whistles, long beeps, or rapid downward sweeps. Bats also emit social calls which are used for communication with other bats and some of these are just within our hearing range, at least when we are younger, and we may hear faint squeaks when bats are flying around close to us. The most audible sounds bats make is when they are chattering inside a roost, particularly as they prepare to emerge around sunset. Recordings of bat calls heard on different bat detectors can be found here
How much do bats help to control pests?
We don’t like using the term pest but if you mean insects that damage crops or gardens, we know that over 70% of all bat species feed on insects and as such play an important role in controlling insect numbers. UK bats do not suck your blood – but they will help clear the air of bloodsucking mosquitoes and midges!
There are many studies demonstrating the “ecosystem services” that bats provide. For example, the Brazilian free-tailed bat has been recognised as an important “insect management service” in cotton farming, resulting in an estimated $740,000 per year reduction in costs of pesticides and loss of crops in Southern Texas.
Why do bats swarm?
Bats have complex social lives that we are still uncovering. Swarming is a form of breeding behaviour, which in Britain and other temperate regions usually occurs in late summer. As maternity roosts disperse, bats congregate at caves, tunnels and other sites that will later be used for hibernation.
These gatherings are noisy affairs (though you wouldn’t know it unless you have a bat detector) and bring together bats from many colonies for breeding, making them important for gene flow within populations.
Other bats gather at mating arenas called leks, where multiple males display with wing flaps and calls to advertise themselves. If they catch a female’s attention, they may try and endear themselves by grooming her, as a prelude to wrapping wings around her and mating. But in some bat species, each male maintains his own territory. He’ll patrol it with frequent song flights to lure passing females.
This Q&A originally appeared in BBC Wildlife Magazine, and was answered by Laurie Jackson.
Do bats use song for courtship?
Male bats do sing to woo potential mates, but unlike most birds they can also use sound to navigate and hunt food. In fact, bats use noise for many types of communication – for example, distress calls, chittering within a roost, and pups calling for their mothers. Social calls tend to be much lower in frequency than the ultrasonic ‘tweets’ of echolocation calls. In some species calls are even low enough for humans to hear. Social calls also tend to be more complicated, sounding like a series of undulating trills that are quite beautiful to hear.
In the UK the most common time to hear bat social calls is in early autumn when bats start mating and preparing for winter. One West African species, the hammer-headed fruit bat (Hypsignathus monstrosus), has some of the loudest bat courtship calls, where males gather in groups or ‘leks’ and use their huge noses and voice boxes to produce deafening honking sounds to attract the ladies.
What is the farthest a British bat has flown?
This accolade goes to a female Nathusius’ pipistrelle, which flew a whopping 2,018km from London to the Russian village of Molgino, setting a new British record. It’s one of the longest known bat travels globally, and the furthest known from Britain across Europe. The pip weighed just 8g, and despite her Herculean effort, fell prey to a cat.
This Q&A originally appeared in BBC Wildlife Magazine.
How does the Bat Conservation Trust (BCT) help bats?
The Bat Conservation Trust supports local bat groups across the UK and over 5,000 members. It works with volunteers, scientists, businesses and government locally, nationally and internationally on a range of projects.
Key activities include running the National Bat Helpline, which handles thousands of enquiries per year from members of the public seeking advice; the National Bat Monitoring Programme, a long-running citizen science project which tracks changes in many of the UK’s bat populations; biodiversity policy and advocacy, including developing best practice guidelines for bat conservation, responding to policy and lobbying government; working with different sectors of industry such as building, agriculture and woodland management to help conserve bats and their roosts; education and outreach; training volunteers and professionals in bat survey methods; supporting and collaborating on scientific research; and collaborating on projects to improve landscapes for bats.
What can the public do to help?
Anyone can make an important contribution to bat conservation. There are many actions you can take if you think bats are under threat in your local area, you find a bat that needs some help, or you simply want to do the right thing if you have bats on your property or in your garden (bats.org.uk/advice).
There are many rewarding ways of supporting bats, for example, making your garden more bat-friendly, or becoming a member of the Bat Conservation and/or your local bat group (bats.org.uk/support-bats). There are various ways you can volunteer your time to support bat conservation, for example becoming a bat carer, taking part in local bat group projects, or discovering and counting your local bats through the National Bat Monitoring Programme.
