There are 18 species of bat resident in the UK from two families (Rhinolophidae – Horseshoe bats and Vespertilionidae – Evening bats). The smallest is the Pipistrelle bat, which can weigh as little as 4 grams (the equivalent of 10 paper clips); and the largest, the Mouse-eared bat, which can weigh up to 45g. All British bats are insectivorous, and use echolocation to find their insect prey.

Bats are distributed throughout the UK, with greater diversity in the south-west. Species distribution is related to climatic conditions.

The abundance of bats in any given area is related to the availability of suitable roosting sites within close proximity to good foraging grounds. These can include woodland, hedgerows, lines of trees, orchards, parkland, scrub, gardens, street lights, watercourses, waterbodies, wetlands, grazed pasture and meadows.

Bats require different conditions in their roosts depending on the time of year. During the summer, females form nursery colonies in warmer sites such as buildings, trees and bridges to give birth and raise young. Bats typically give birth to only one pup per year. During the winter months both sexes hibernate in cooler underground sites such as trees, buildings, bridges or underground structures.

Different species also have varying requirements ranging from bats that are primarily tree roosters, such as the Noctule, through to bats that generally roost in buildings, such as the Serotine.


All species of British bat and their roosts are protected under British law by the Wildlife and Countryside Act 1981 (as amended), which is extended by the Countryside and Rights of Way Act 2000. Bats are classified as European Protected Species under the Conservation (Natural Habitats, etc.) Regulations 1994. Together, the legislation make it illegal to:

intentionally or deliberately kill, injure or capture (or take) bats;

deliberately disturb bats (whether in a roost or not);

recklessly disturb roosting bats or obstruct access to their roosts;

damage or destroy bat roosts;

possess or transport a bat or any part of a bat, unless acquired legally;

sell, barter or exchange bats (dead or alive) or parts of bats.

A bat roost is interpreted as “any structure or place which any wild bat...uses for shelter or protection”. As bats tend to re-use the same roosts, moving around seasonally, a roost is legally protected whether or not bats are present at the time.




Any development that could impact on bats requires survey work to be carried out and an impact assessment conducted.

Some survey work can be carried out without a licence such as dawn, dusk and activity surveys. However, any work involving disturbance to bats requires the surveyor to carry a licence issued by Natural England, the Countryside Council for Wales, Scottish Natural Heritage or the Environment and Heritage Service in Northern Ireland.

RSK Carter Ecological carry out a number of surveys including:

Initial habitat assessment – an assessment of the potential of a site to support roosting, commuting and foraging bats.

Building or bridge survey – our licensed ecologists investigate buildings and bridges for bats or signs of bat use.

Tree surveys – our qualified tree climbers investigate trees for bats or signs of bat use.



Underground site survey – ecologists with confined spaces training investigate underground sites for bats or signs of bat use.

Dawn and dusk survey – trained ecologists watch for bats leaving and returning to their roosts respectively, allowing for the identification of roost sites. This provides confirmation of species identification, population estimates, roost status and access points.

Bat activity survey – trained ecologists listen for bats commuting and foraging using bat detectors and recorders to enable analysis of bat echolocation calls, which are unique for each species.

The timing of survey work is sometimes restricted to a small window during the year therefore it is better to plan surveys in as early as possible.


A European Protected Species License, is required before the commencement of any development that might impact on bats or their roosts. A licence application includes details about bat species, population levels, roost status and a detailed mitigation strategy for the site.

The mitigation strategy outlines how the developer intends to avoid harm to bats during the works and can include avoiding sensitive months such as early May to late August, when bats are breeding, and early November to late May, when bats are hibernating. Disturbance to breeding bats can potentially jeopardise successful reproduction. Disturbance to hibernating bats can reduce survival rates through the winter. Recommended months for starting works include April and September/October. When works start it may be necessary to implement an ecological watching brief to supervise some of the works.

All mitigation strategies involve provision of bat roosting sites (or commuting and foraging grounds) for the future. This ranges from the erection of bat boxes around the site to a dedicated bat attic in a building or a purpose built bat roost. Provision of commuting and foraging grounds may include the retention of vegetation or a planting strategy.

Processing of licence applications takes at least 30 working days. License applications are determined by Natural England through consultation with the local planning authority.