Please note: All views and opinions expressed in this article are purely those of the author. The content cannot necessarily be taken to represent the specific policy of any of JP Associates’ developer clients.

As a protected species bats require due consideration on development sites. Forward planning of the necessary surveys can save time and money.


There are 16 species of bat which are currently known to breed within the British Isles. All of these species have been subject to population declines to differing levels and are subject to high levels of legal protection to benefit their conservation.

The South West is especially important for bats as all 16 species can be found there, including both species of horseshoe bat which are subject to much targeted conservation work due to their restricted range and significant declines over the past 100 years.

Basic ecology

Bat species vary in their habits, and it is essential to take these into account where their presence affects a proposed development. However there are general similarities that are important to know.

Bats are nocturnal mammals, and all British bats feed upon insect prey. Bats use echolocation by emitting ultrasonic pulses in order to navigate and detect prey in the dark.

There is a marked seasonal variation in their activity and behaviours. During winter months bats will select roosting sites suitable for hibernation that are buffered against rapid temperature changes and that can maintain relatively high humidity levels. During the winter, activity is much reduced and bats will fly less often. Activity levels increase during the spring and they are much more likely to be seen flying from April through to October. Female bats often gather in maternity roosts to have their young, and peak numbers of births occur in mid to late June. Usually a female bat will have a single pup which is dependent for between three and five weeks. Favoured roosts vary between species, local habitats and the time of year, but may include man-made structures such as buildings, bridges, tunnels and mines as well as trees and caves.

Bats are relatively long-lived creatures, with some British bats known to have lived in excess of 30 years. Their roosting and foraging habitats are often used year after year and can be extremely important for a given local population.


All bat species within Britain are listed within Schedule 5 of the Wildlife and Countryside Act 1981and Schedule 2 of the Conservation (Natural Habitats & c.) Regulations 1994. Under these pieces of legislation (and their subsequent amendments) it is an offence (amongst other actions) to:

  • intentionally or deliberately kill, injure or take bats
  • deliberately disturb bats (within a roost or not)
  • recklessly disturb roosting bats or obstruct access to their roosts
  • damage or destroy roosts (whether bats are present or not).

For the purposes of the legislation a ‘roost’ is any structure or place which any wild bat uses for shelter or protection. Roosts are protected irrespective of whether bats are present or not at a specific time, due to the seasonal nature of many roosting sites.

There are exceptions to these rules, but in almost all development situations these statements must be adhered to. Prohibited actions can only be made legal if a European protected species licence (EPSL) is issued by Natural England.

Determination of presence

Bats have been shown to use many different locations to roost, and therefore a wide variety of sites must be considered as potential bat roosts. Thought should be given to bats being present in, for example, buildings, trees, caves, mine workings, cellars, tunnels and bridges.

Other habitat features important for bats such as hedgerows, woodland, water courses and permanent pasture which may have importance as commuting or foraging routes should be considered too. Removal or degradation of important habitat can have significant negative effects upon local bat populations.

Surveys are important to deduce whether bats use a site as a roost or a particular habitat for commuting and foraging. The type of survey used will largely depend on the time of year, the individual site features and the ultimate purpose of the survey. In many cases more than one type of survey, at different times of day or year, are required. Some of the most common surveys where developments are concerned are bat roost surveys and flight activity surveys.

1. Bat roost surveys

Surveys of buildings, bridges, specific trees and underground sites may be targeted for the presence of a bat roost. Survey methods will vary depending upon the site, but will basically look for particular signs that show bats are using the site, including bat droppings and feeding remains. From these indicators it is sometimes possible to tell which type of bat species uses the site. As well as determining the presence of a roost surveys also aim to make informed opinions as to how the site is used by bats and the level of importance the roost represents to the local population. Surveys of roosts can be carried out at anytime of year, as signs of bat presence will often remain even if it hasn’t been used for several months. Sites which are suspected to be used as hibernation roosts require extra care and attention when surveying, as arousing bats in torpor can have detrimental effects upon their survival.

2. Flight activity surveys

Where potential roosts cannot be surveyed directly, such as roosts that are within extensive habitat or where bat usage of habitat is being determined, it is necessary to carry out a flight activity survey, including dusk emergence and dawn re-entry surveys. Survey methods will vary depending upon the site and survey purpose, but generally involve surveyors using bat detectors to detect ultrasound emitted by bats and by visually monitoring bat movement. Bat detectors convert ultrasound emitted by bats into a series of audible sounds. It is often possible to determine the species or group of bats present based on the type of sound and frequency that is detected. Flight activity surveys are limited to months when bats are usually seen flying (typically May through to September), as well as when weather conditions are suitable – they are less likely to fly when it is wet, cold or windy.


Where proposed developments are deemed to affect bats, a European protected species licence (EPSL) must be obtained from Natural England before construction works may take place. Licences may be issued for reasons of overriding public interest (which may include a development) on the basis that there is no satisfactory alternative, and that the actions will not be detrimental to the overall conservation status of bats.

Licensing processes may take a considerable time to complete and forward planning is recommended. Strategies to mitigate and compensate for the impact of the development should be planned early in the proceedings. The aim of such measures should be to maintain and preferably enhance populations affected by development. Mitigation and compensation measures should be proportionate to the impact of a development, and based upon adequate knowledge. Good initial surveys and impact assessments are extremely important when planning such measures. A method statement outlining a developer’s plan to mitigate and compensate with regards to bats will be required in any application for an EPSL.

Potential impacts of developments on bats include:

  • loss of roosts and potential roosting sites
  • loss or degradation of commuting and foraging habitat (hedgerows, woodland, permanent pasture, trees), leading to habitat fragmentation
  • the effects of illumination. Bats can be extremely sensitive to artificial light and may avoid illuminated areas or become susceptible to higher levels of predation.

Impact level will vary depending on the species of bat, the way the site is used by bats, the number of bats using a site, and the amount of habitat affected.

Considerations when planning mitigation and compensation:

  • adjusting plans and layouts of developments to reduce impacts on bats to include
    • avoidance of impact on existing roosts
    • maintenance and enhancement of existing corridors of habitat for commuting bats
    • maintenance and enhancement of foraging habitat
    • incorporating lighting sensitive to the needs of bats.
  • timing of works to limit disturbance to any roosts
  • incorporating existing roosts into plans
  • providing new habitat and roosting opportunities and ensuring long-term management so that populations will persist
  • informing all construction workers of bat presence and their responsibilities.

It is extremely important to remember that mitigation and compensation may take some time. Some works may need to be completed outside certain times of year, or new roosts colonised before existing ones can be destroyed or modified. Early planning should avoid delays to proposed work schedules.


  • All bat species in Britain are European protected species and afforded high levels of legal protection, including from killing, injuring, and damage to their roosts.
  • Bats have been found to roost in a wide variety of locations including buildings, trees, bridges, tunnels and caves.
  • Bats have marked variations in their seasonal activity, which will affect where they roost, when they can be surveyed and when certain construction works are likely to be allowed to take place.
  • Licences can be obtained from Natural England to allow actions which are usually deemed illegal.
  • Mitigation and compensation measures must be considered where bats are affected, and should be proportional to the impact of any development and based upon knowledge gained from surveys.



BAT CONSERVATION TRUST. 2007. Bat Surveys – Good Practice Guidelines. Bat Conservation Trust, London.

MITCHELL-JONES A.J. 2004. Bat Mitigation Guidelines. Natural England, Peterborough.

MITCHELL-JONES A.J, AND MCLEISH A.P (eds.). 2004. Bat Workers Manual, 3rd Edition. JNCC.

SCHOFIELD H.W, AND MITCHELL–JONES A.J. 2003. The Bats of Britain and Ireland. The Vincent Wildlife Trust.