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Bats

Background

There are 18 species of bat recorded in the UK of which 17 are known to breed.  Bats rely on shelter away from predators, and a constant source of water and insects to survive. They are largely nocturnal, spending daylight hours in sheltered locations before emerging at night to forage for insects.

Brown long-eared bat

Brown long-eared bat (Plecotus auritus)
Photo © Gilles San Martin

The place a bat lives is called its roost. Bats need different roosting conditions at different times of the year, and will often move around on a regular basis to find the condition that meets their needs.  Roost choice varies with species (as well as time of year) and can include trees, buildings, other built structures, bridges and underground sites such as caves, mines and tunnels.  All UK bat species will make use of buildings on occasion, but for some species, buildings are essential as roost sites. This situation has arisen over a long period of time as tree cover and availability of caves, which would have provided natural roost sites, have become scarce.  Around three quarters of British bat species are known to roost in trees. Since bats are not able to make holes or nests they will use whatever gaps in trees are available to them, made by other animals, or by the natural decay of the wood or from arboricultural actions. Bats may use different roost locations within a building or tree,  depending on time of year, ambient temperature and a variety of other reasons.

Bats are not blind, but to fly around and hunt for insects in the dark they use a high frequency system called “echolocation” that is similar to sonar. Bats make calls as they fly, sensing the returning echoes to build up a sonic map of their surroundings. The bat can tell its distance from an object by how long it takes the sounds to return to them. These calls are usually pitched at too high a frequency for adult humans to hear naturally – but they can be heard by using a device called a bat detector which ecologists can use to provide information on bat species and their activity.

During the winter (and at other times of year when weather conditions are poor) bats will slow down their metabolism, entering a period of torpor in response to cold weather and an associated lack of available insect prey .  Bats mate in the autumn, prior to their winter hibernation. Females store sperm and do not become pregnant until the spring when the weather gets warmer. Pregnant females gather together in maternity roosts to have their young and often the same individuals return to the same site each year.

Brown long-eared bat maternity roost in a Coach House in Norfolk

Pregnancy lasts 6-9 weeks depending on the species, and can be influenced by availability of food and the climate. Females usually give birth to a single pup each year.  Bats are very sensitive to disturbance during the maternity season (May-August) and may abandon their young if this happens. For 4-5 weeks the young are suckled by their mothers until they are old enough to fly and begin to venture out from the roost to forage for food.

Conservation status

Daubenton's bat caught in a mist net during roost emergence survey - Bishop's House, Ely

Daubenton's bat caught in a mist net during roost emergence survey - Bishop's House, Ely

Bats are present across the UK and the Republic of Ireland, with 18 known species of bat resident in the UK (of which 17 are known to breed) and 10 species resident in Ireland.

Bat populations are threatened by loss and fragmentation of natural hedgerow, woodland and pond habitats, loss of food due to pesticide use and intensive agriculture, and building and development work affecting roosts.  Populations have declined over the last hundred years and are still threatened into the 21st century.

Legislation

In England and Wales, bat legislation is the Wildlife and Countryside Act (1981) (as amended); the Countryside and Rights of Way Act, 2000; the NERC Act (2006); and by the Conservation of Habitats and Species Regulations (2010). In Scotland, the key legislation that applies is the Conservation (Natural Habitats &c.) Regulations 1994 (as amended). In Northern Ireland bats are listed under Schedule 2 of the Conservation (Natural Habitats etc) Regulations (Northern Ireland) 1995 and, in the Republic of Ireland, under Schedule 5 of the Wildlife Act 1976 and Schedule 1 of the European Communities (Natural Habitats) Regulations 1997.

It is an offence for anyone intentionally to kill, injure or handle a bat, to possess a bat (whether live or dead), disturb a roosting bat, or sell or offer a bat for sale without a licence. It is also an offence to damage, destroy or obstruct access to any place used by bats for shelter, whether they are present or not. Barbastelle, soprano pipistrelle, greater horseshoe, lesser horseshoe, Bechstein’s, brown long-eared and noctule bats are all priority species under the UK Biodiversity Action Plan (UK BAP) and have also been adopted as species of principal importance in England under Section 41 of the NERC Act 2006.

Licensing

Barbastelle bat droppings

Barbastelle bat droppings from a barn in Cambridge

Some bat work can be carried out without holding a licence of any kind. Both volunteers and professionals can carry out the planning stages of a bat survey and do bat detector activity surveys without requiring a licence. A licence is only needed once it has been established that bats are present.   Applied Ecology Ltd employ ecologists who hold the necessary survey licences to disturb and take bats by hand, static hand-held net, mist net and harp trap as well as to use sonic lures to attract bats to nets and traps.

Survey

In relation to UK planning and development, a bat survey would usually take the form of an initial inspection of any building, tree or other potentially suitable feature for roosting bats that could be adversely impacted by a development proposal.   A search would be made for physical evidence of bat presence such as the presence of live bats, their droppings and feeding remains.  If evidence is found, or if (in the absence of any evidence) bats are still suspected to be roosting on site, a follow up survey by a licensed ecologist may be required.

A follow-up survey would typically involve conducting an after dark bat activity survey to determine the number of each bat species present and (if possible) the exact roosting locations of those bats within the site.  Comprehensive guidance has been published on the scope and survey effort required to conduct bat survey work, with activity surveys being best undertaken to coincide with the main bat active period of April-September.

So called bat roost emergence and return surveys (at dusk and dawn respectively) are used to identify the location of features used by bats to gain access to or leave a roost, and also to identify the number of bats of each species using a particular roost.  They are also an important means of proving that bats are not roosting on site.

Soprano pipistrelle bat emerging from a maternity roost in Cornwall

We operate a range of survey equipment to assist bat activity survey on small and large scale projects.  We are equipped with a large number of state of the art electronic bat detectors, automated bat survey equipment, harp trap and sonic lure, and use infra-red video and lighting to assist with activity surveys.

 

Automated electronic bat detector in purpose-built wooden housing

Long-term automated bat detector survey of ancient woodland in Essex

Assessing the potential impact of floodlighting on bats at Lords Cricket Ground

Assessing the potential impact of floodlighting on bats at Lords Cricket Ground

 

Mitigation

From a bat conservation perspective often the best development option (and often the most economically viable) is to preserve existing bat roosts and habitats.  However, this is generally only achievable when ecologists have been involved at an early stage, and bat roosts and foraging patterns have been identified before devleopment plans are too far advanced. If a development related activity is likely to result in an adverse impact on bats and their roosts, i.e. on the basis of survey information and specialist knowledge of the species concerned, and the consultant ecologists consider that on balance the proposed activity is reasonably likely to result in an offence under Regulation 41 of The Conservation of Habitats and Species Regulations 2010, a European Protected Species (EPS) mitigation licence would be required to legally enable the work to commence.

Applied Ecology Ltd ecologists have successfully applied for EPS licences on behalf of developers across the UK, and have extensive experience in bat roost mitigation and compensation planning.

Bat roost creation as part of Ely Catherdral roof refurbishment

Bat roost creation as part of listed barn restoration at Shuttleworth College

 

Bat videos

Barbastelle bat summer roost, barn ridge beam, Cambridgeshire


Brown long-eared bat maternity roost, Cambridgeshire

Brown long-eared bat summer roost, barn mortice and tenon joint, Guildford


Daubenton’s bat maternity roost, Bishop’s House, Cambridgeshire

See Survey Calendar for survey timings.

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