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Preliminary Roost Assessment survey
A Preliminary Roost Assessment survey (often called a Bat Roost Potential survey) can be undertaken at any time of year.
This survey identifies whether a building, structure or tree has evidence of, or the potential for, use by roosting or hibernating bats. This involves a thorough search for bat droppings, feeding debris (such as moth and butterfly wings) and features that may accommodate roosting bats, such as cracks in walls, gaps under roof tiles or old woodpecker holes in trees.
It may be possible to rule out the potential presence of a bat roost at this stage.
An assessment of habitats surrounding a building, structure of tree is also carried out in conjunction with a Preliminary Roost Assessment to help determine the suitability of a site to support commuting and foraging bats. This assessment can be carried out at any time of year, and may be undertaken as part of a Preliminary Ecological Appraisal.
Nocturnal bat surveys
Nocturnal bat surveys are often required when evidence of, or potential for, roosting, commuting or foraging bats, is identified from the Preliminary Roost Assessment or habitat assessment survey.
Nocturnal static roost assessment surveys are undertaken at dusk and prior to dawn using specialised detecting equipment to determine how bats may be using a building, structure, tree or habitat, and what species of bat and type of roosts are present. Static surveys are seasonally restricted, and are generally undertaken between May and September, with the optimum time to survey being between May and August.
Nocturnal transect activity surveys may be required if a development or an activity is going to have a significant impact on potential bat commuting or foraging habitat. Nocturnal transect surveys involve surveyors following predetermined routes around a site, with automated bat detectors strategically positioned at locations along this route. Transect surveys can be undertaken between April and October; the extended survey period covering transitional periods of bat activity (spring and autumn) when bats are generally moving to and from summer and winter roosts.
Hibernation surveys
Hibernation surveys may be required if a building, structure or tree offers features that provide a stable, cool and humid environment that will allow a bat to enter into deep torpor (hibernation) throughout the colder months. In the UK bats generally enter deep torpor between December to February, however torpor bats may be present at hibernation roost sites during the months of November to March. During the hibernation period bats will rouse during warmer nights to move location and occasionally feed.
A hibernation survey involves a detailed inspection of suitable hibernation features within a building, structure or tree to search for evidence of hibernating bats. Automated bat detectors may be installed internally for a period of several weeks within buildings or structures to monitor and record bats that could be active on warmer nights.
The optimal time to carry out hibernation surveys is between December and February, although earlier or later surveys may be appropriate depending on several factors i.e. bat species likely to be roosting, prevailing weather conditions and characteristics of the roost feature(s).
Timing of surveys
- Preliminary Roost Assessment survey – any time of year;
- Nocturnal bat surveys – May to September (April to October for transects and suspected transitional roosts);
- Hibernation surveys – December to February (November to March depending on site specific factors).
All bat surveys are supervised/undertaken by Natural England licenced ecologists.
Bat surveys may take up to a year to complete if conditions are present that will allow bats to use a site all year round.
Mitigation and licencing
When surveys are complete, a full Ecological Impact Assessment of a proposed development or activity can be made and an appropriate and practical bat mitigation strategy can be devised and agreed. Even if bat activity is identified it may be possible for a development or activity to proceed following a precautionary working methodology to prevent disturbance of bats or damage/destruction of their roosts.
If this is unavoidable then a European Protected Species Licence or a Bat Mitigation Class Licence can be obtained to permit the project to proceed. The content of the licence will vary on a site by site basis but usually includes sensitive timing of works, hand capture and re-location of bats, and providing suitable replacement roost sites.
Legislation
Bats are afforded full protection under the 1981 Wildlife and Countryside Act (as amended) and the Conservation of Habitats and Species Regulations 2017.
This makes it an offence to kill, injure, capture or disturb bats, or obstruct access to their roosts/resting places or destroy roosts/resting places in Britain.
Note
The above information is based on standard guidelines and current UK legislation. Every site is unique so please contact a Torc Ecology consultant who will advise on the best survey approach in relation to the project requirements.
Facts about bats!
There are around 18 species of bat currently resident within the UK accounting for nearly a quarter of all British mammal species. Bats live or ‘roost’ in a variety of different places including buildings, trees, caves and tunnels and use different features for breeding, hibernating and resting.
Some breeding sites, known as maternity roosts, can accommodate thousands of bats, whilst bats can also roost individually or in very small numbers.
All UK bats are insectivores with the common pipistrelle bat, the UK most common bat species, eating over 3000 insects in a night.
