October 2014 - Bats

Bawburgh Pipistrelle bat, photo taken by Keith Oldrey

At dusk, in mild autumn weather, you might see one bat or more flitting across your garden. Their high pitched echo location systems enable them to have excellent 'sight' in the dark as they listen to the sounds bouncing off objects around them. Blind as a bat does not apply! 

There are about sixteen species of bat found in the UK, all of which eat night flying insects; 13 of these have been found in Norfolk. The most common bat is the Pipistrelle, which is only 4cm long and weighs less than a 2p coin.  The rarest bat in Norfolk is the Barbastrelle - we are unlikely to see this in Bawburgh! The Brown Long-eared bat is also common in Norfolk. A bat detector (and experience) can identify the various echo location sounds of flying bats and is a useful species identification tool.

Bats live in colonies in roof spaces, or cracks or holes in trees or walls of buildings. Half of known Pipistrelle bat roosts are in houses less than 25 years old. According to the Norfolk Wildlife Trust bats make good house guests: they do not chew through wood or wires; they do not bring in nesting materials and are extremely quiet. In winter, when food is scarce, they hibernate in cool damp places inside buildings, caves or in hollow trees. At this time their heart rate drops to 2 beats per minute, and they live off special brown 'hibernation' fat in their bodies. There have been reports that bats may live 20 to 30 years, although 5 years is more likely.  In summer they give birth to very large babies. An 8 gram mother Pipistrelle may produce a 2 gram baby! I bet she is pleased she only has one a year!

There is evidence to suggest that bat boxes placed in sunny positions are more likely to be occupied than ones in shady positions and darker-coloured boxes (which absorb more sunlight, hence becoming warmer), are more likely to be used than light coloured boxes. In addition, boxes on buildings are more favourable than those put on trees, and Pipistrelles prefer woodcrete (a mixture of sawdust, clay and cement) to plain wood. Studies have shown you need to be patient and possibly wait years before a box is occupied by bats. 

Bats and their roosts are protected under the Wildlife and Countryside Act 1981. It is an offence to block access to their roosting sites and an offence to kill, injure, disturb or handle a bat without a licence.



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