Sunday, 6 April 2008

Bats

The purpose of this article is to dispel any superstitions and misconceptions associated with Bats, and to present you with the real facts about these interesting mammals.

I will write about some of the different species that can be found in the British Isles, and I'll be describing their habitat and behaviour.

I'll also be looking at practical ways in which we can help protect them and prevent their extinction.


Big eared townsend bat (Corynorhinus townsendii)

Almost everybody has encountered bats at one time in their lives. Usually via the media, portrayed as the popular anti-hero in the Batman series of films and comics, or in the 19th century Bram Stoker novel Dracula.

People living or working in rural areas, or those walking in the countryside, will often observe bats in flight, and on very rare occasions may even encounter them at close quarters.

Bats are the only mammals that can fly, unlike the Flying Squirrels that simply glide and are unable to actually fly upwards.

Bats belong to the taxonomic order Chiroptera, which roughly translated means "Hand Wing". The bone structure of their wings is almost identical to that of the human hand, but with very long, thin fingers, joined together by a stretchy membrane of almost hairless skin.

Chiroptera can be split up into two sub-orders: Microchiroptera and Megachiroptera. The former are found in Britain, and predominately feed on insects. They have quite small eyes and rely on echo-location to find food and navigate. The latter generally have larger eyes, which they use instead of echo-location, and usually feed on fruit.

Bats range in size from the diminutive Kitti's Hog-nosed Bat , which is indigenous to Thailand and about 30mm long, weighing around 2 grams.


Kitti's hog-nosed bat (Craseonycteris thonglongyai)

All the way up to the Flying Foxes or Fruit Bats commonly found in tropical climates, which have an impressive wingspan of almost 6 feet and weigh over 2 pounds.


Malayan Flying Fox (Pteropus vampyrus)

Nectar Bats such as the Dekeyser's Nectar Bat also belong to the Megachiroptera sub-class, but instead of eating fruit they use their long tongues and snouts to reach inside flowers and feed on the nectar and pollen within.

The Fish-Eating Bat is one of only a few species of bats that eat fish. It has very long feet and large toes which it uses to grab small fish near the surface of the water.

There are only three bat species that feed on blood: The Common Vampire Bat (Desmodus rotundus), the Hairy-Legged Vampire Bat (Diphylla ecaudata), and the White-Winged Vampire Bat (Diaemus youngi).

The Vampire Bat is a blood drinking bat (sanguivore) that usually feeds on the blood of horses, donkeys, pigs, goats, cattle and birds.


Common Vampire Bat (Desmodus rotundus)

Contrary to popular belief, Vampire Bats do not have fangs which they use to pierce the skin. They actually have razor-sharp upper incisor teeth, with which they make a small, painless incision, and then lap up the blood.

As with many other sanguivores, their saliva contains several ingredients that prevent the blood clotting and prolong bleeding. One of which, a Glycoprotein called Draculin, is of particular interest to pharmacists for its remarkable anticoagulant properties which may be beneficial to heart attack and stroke patients in the future.

Vampires: The Real Story contains a wealth of information for anyone interested in finding out the truth about vampire bats. It's written by two well-known experts in the field and does an excellent job of debunking the myths associated with vampire bats.

Bats can be found almost everywhere on Earth, but not in very hot or very cold climates. They inhabit all continents except Antarctica.


Indiana bat (Myotis sodalis)

Bats generally try to find a shelter that offers some form of protection from predators, usually somewhere high up or with a narrow opening.

The most common roost sites are to be found in trees and caves, where bats seek out cavities and crevices to squeeze into. They also roost in buildings, tunnels, walls, mines and bridges.


Little brown bats (Myotis lucifugus) in Endless Caverns, Virginia, USA

There are two major factors which influence their choice of roosting site:

  • Temperature
  • Humidity
Female bats tend to choose hot sites when pregnant because bat embryos develop much more slowly when cold. Males prefer cooler roosting sites in summer, where they can conserve their stored energy.

When a bat has found a roosting site, it enters and hangs upside down from a suitable surface by its feet. In highly populated roosts it is not uncommon for bats to be found clinging to one another.

In temperate climates, bats usually mate in the autumn or winter. The females then carry the males' live sperm inside them through the hibernation period, ovulate in spring and then become pregnant. In more tropical areas, fertilisation occurs immediately after mating, followed by development of the embryo and birth.

Mother bats typically give birth to only one offspring per year, but some species can have up to four. A baby bat is referred to as a Pup, and although the ability to fly is congenital, at birth the wings are too small so they cling to their mother for transport.

Young microchiroptera become independent at the age of 6 to 8 weeks, megachiroptera around four months old. At the age of two years, bats are sexually mature.

In temperate climates, bats hibernate between October and April. During this period, their metabolism and internal organs slow down, their body temperature decreases, and they become torpid. They do this in order to save energy when food is scarce. It is very important that they are not disturbed while hibernating, otherwise they may use up some of their fat reserves when they wake up.

The hibernation site is referred to as a Hibernaculum, and is carefully chosen by the bat. It has to have just the right amount of humidity (otherwise the bat will dehydrate), be inaccessible to predators, and not have any extremes of temperature.

Contrary to popular belief, bats have excellent eyesight which they supplement with a sophisticated high frequency echo-location system. They emit a series of inaudible (to humans) ultrasonic chirps, clicks, and barks, which usually sweep from high to low frequencies, or vary around a particular frequency. By looking at these frequencies and other characteristics of their calls, we can identify the species of bat.

This can easily be achieved with the use of a heterodyne detector such as the Magenta Bat4. I would also recommend purchasing The Bat Detective which is a guide to identifying bats. It includes an excellent audio CD containing 48 tracks of 13 British bat species.

There are over 900 different species of bats throughout the world, but only 17 of those are found in the British Isles:
Six of these are designated as rare, two as endangered, and six vulnerable.

There have been one or two sightings of the Greater Mouse-Eared since it was declared exctinct in the UK in 1990. Sadly, there have been no further reports.


Skeleton of a Greater Mouse-Eared Bat (Myotis myotis)

The following bats can be found in Suffolk:
  • Common Pipistrelle
  • Soprano Pipistrelle
  • Lesser horseshoe
  • Natterers
  • Daubentons
  • Whiskered
  • Brandts
  • Noctule
  • Leislers
  • Serotine
  • Barbastelle
  • Brown long eared
Pipistrelle are the most common species found in the county, and the most frequently encountered roosting in buildings.


Common Pipistrelle (Pipistrellus pipistrellus)

The Pipistrelle is Britains smallest bat and appears to be abundant and widespread throughout the rest of the country.

I often observe Soprano Pipistrelle flying over the River Lark, where they hunt for small insects which are caught and eaten in flight. They echo-locate at a peak frequency of around 55KHz, whereas Common Pipistrelle echo-locate at a peak frequency of 45KHz.

Habitat plays an extremely important role in bat ecology, of particular importance is Arboreal habitat. Bats are very dependent upon having a wide variety of roosting sites, research suggests that bats may occupy over 30 different sites during the summer. Not only do trees provide a roosting site for bats, they also serve as shelter for the insects that bats feed upon.

We can all do something to help conserve bats and their habitats, here are some ideas:
  • Put up bat boxes
  • Make your garden attractive to wildlife
  • Don't cut down dead trees
  • Join your local bat group
  • Take part in the European Bat Weekend
  • Take part in the National Bat Monitoring Programme
  • Join the Bat Conservation Trust
Bats need a wide variety of roosting sites, you can give them more choice by putting up a simple bat box. Building a bat box, Bat Boxes, and How to make a bat box (PDF) are all excellent tutorials. Always remember to use untreated wood, because many wood preservatives can kill bats.

On a much larger scale, Hibernaculums like this one at Thetford Forest can be built to provide a winter home for the bats. It will allow bat numbers to be closely monitored, and may help to protect some of the rarer species such as the Barbastelle.

By making your garden attractive to wildlife you'll be encouraging a wide variety of insects, which in turn, will attract bats. The insects will pollinate your plants, the plants will reproduce and attract more insects, and the bats will keep the insect population in control. Your garden will also become a home for other natural predators such as garden birds, hedgehogs, ladybirds, and spiders. It's the ideal way of encouraging biodiversity! How do I attract bats to my garden? (PDF)

Dead trees are an ideal habitat for insects, as well as providing a roost site for bats. They encourage a large diversity of different insects including moths, caterpillars, centipedes, beetles, aphids, and other invertebrates. Some species of bat have been known to roost beneath the exfoliating bark commonly found on dead trees.

If you join a local bat group you'll have an opportunity to meet other like-minded individuals, to attend conferences, and to take part in surveys and guided walks. You'll usually receive a regular newsletter keeping you up to date with your groups activities. Take a look at Local bat groups to locate a group near you.

The Suffolk Bat Group is one of 90 bat groups nationwide whose primary aim is to protect bats. They achieve this remarkable feat by advising the public, carrying out surveys, enhancing and creating hibernation sites, and establishing bat box projects.

By taking part in the European Bat Weekend you'll be able to learn more about the problems facing bats, and to find out how you can help. There will be hundreds of organised bat walks and talks. Look here for an update

When you sign up to the National Bat Monitoring Programme you'll be assisting with a nationwide survey. The data collected is analysed to discover any trends or fluctuations. This information allows us to assess the conservation needs of British bats, and to focus our efforts more efficiently. Regardless of your current knowledge or experience, the NBMP will have a survey suitable for you.

By joining the The Bat Conservation Trust you'll be helping to raise much-needed funds for a variety of bat conservation projects. With your help they can monitor bat populations, support local bat groups, provide training, teach the public about bats, and operate a bat helpline.

So what do bats do for us? Bats are beneficial in a number of ways:
  • Bats control insect populations
  • Bats are helpful to farmers
  • Bats pollinate plants and trees
  • Bats have been used in the development of vaccines
  • Vampire bat saliva has pharmaceutical properties
  • Echolocation has been used to develop navigational aids for the blind
  • Bat droppings (Guano) are an excellent fertiliser
  • Bats have been used in the study of space science
I'm sure you'll agree that bats are very helpful creatures, but most of what they do for us usually goes unnoticed, or gets taken for granted.

If you'd like to find out more about bats I would suggest reading some of the following books:

Bats (Life) - by Phil Richardson - ISBN 0565091670
Bats: Biology and Behaviour - by John D. Altringham - ISBN 0198503229
Bat Ecology - by TH Kunz - ISBN 0226462072
British Bats - by John D. Altringham - ISBN 0002201402
Bats (British Natural History) - by Phil Richardson - ISBN 1873580509

All species of bats are protected by the Wildlife and Countryside Act 1981, please read Bats and the law for further information.

All images courtesy of Wikimedia Commons

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