The life-cycle of bats and the threats to their existence

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Guest writer Ross Stevens delves into the world of bats and finds that many species are facing an uncertain future as human society continues to encroach on their natural habitat. 

There are 18 species of bat in the UK (over one quarter of all British mammal species), with 17 species known to breed.  Bats are unique amongst mammals, as they are the only group to truly fly – squirrels and possums can only glide for limited distances.  Most bats, including all of the British species, are insectivores, and do not feed on blood.  Britain’s most widespread bat, the common pipistrelle, can eat 3,000 midges per night.  Overseas, fruit and nectar feeding bats perform a vital ecological role by dispersing seeds and pollinating flowers, with many tropical plants entirely dependent on bats.

Recently, bats have been swarming together in large numbers to breed. Females generally give birth to only one offspring per year in summer, due to the mother’s need to fly while pregnant, and nurse their youngster until it has grown nearly to adult size.  This does not take long, as pups are a third of the size of the mother when born.  Female bats use a variety of strategies to control the timing of pregnancy and the birth of young, and can even pause the pregnancy when insects are scarce.

Many people believe that bats are blind, when in fact they can see almost as well as humans.  However, to fly and hunt insects in the dark, bats require a remarkable high frequency system called echolocation, which work in much the same way as sonar.  Bats make calls as they fly, and listen to the returning echoes to build up a sonic map of their surroundings.  Noctule bats, the largest of the British bats, echo-locate at such a volume (four times the legal limit of a night club) that it is necessary to disconnect the bones in their inner ear whilst calling so as not to deafen themselves!  Thankfully, these calls are pitched at too high a frequency for humans to hear naturally.  Conversely, brown long-eared bats echo-locate very quietly so as not to alert prey items, so require large ears to hear their own calls.

The threat to their existence

Like many creatures, bats are suffering as natural habitats such as hedgerows, woodlands and ponds have been declining and fragmenting.  Many bat species roost in buildings and so are extremely vulnerable to the activities of humans.  Bats in buildings are under direct threat if they are present whilst works are under-way, or if a demolition is taking place.  Bats may suffer injuries, abandon babies, or even be poisoned by toxic chemicals used for timber treatment in loft spaces.  Also, the use of pesticides and intensive farming practices have lead to a reduction in the abundance of insects which the bats rely on as their only food source.  More recently, it has been suspected that wind turbines may adversely affect bats, as pressure changes around the turbine blades are believed to cause fatal lung injuries. This is a theory that requires further research, in a time when green energy is becoming increasingly widespread.

It is important that we create new suitable habitats and manage and enhance existing habitats to aid in the recovery of bat populations in our towns and countryside.  Due to their decline, all bats are protected by law, and it is illegal to damage, obstruct or destroy a bat roost, or to disturb, capture, injure or kill a bat.  If you would like to know more about bats, information can be found on the Bat Conservation Trust website (www.bats.org.uk) and on the Total Ecology site.

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