What to expect from a bat survey?
You may have been asked by the local council, your architect or planner for a bat survey but what does this mean?
A bat survey is broken into two parts, an initial inspection called a preliminary roost assessment and emergence/re-entry surveys.
Preliminary roost assessment
A preliminary roost assessment can be undertaken at any time of the year. The assessment is an internal and external inspection of the building which is subject to planning. An experienced bat surveyor will look at the condition of external features on the building such as roofing tiles/slates, eaves and chimney and assess the potential for roosting bats. An internal inspection of any lofts and cellars will also be undertaken. Within the loft, all areas will be inspected for the potential presence of bats and any evidence of bats such as droppings, feeding remains or staining. This includes searching the ridge and looking around any hanging felt or within brick cavities.
The building will have been classed as having ‘potential for bats’ if bats or bat evidence is found or if there are features such as gaps in roofing tiles that are suitable for crevice dwelling bats (which cannot be adequately inspected). If the building has potential for bats, further surveys may be required in the form of emergence and re-entry surveys. Where droppings are found, these are collected as a complementary method to the emergence/re-entry surveys, the droppings are sent off to a laboratory for DNA analysis to tell us the species of bat present. This is often used because bat poo can be difficult to identify to species level and some species such as the Long-eared bats require analysis to differentiate them if not physically caught by hand.
If no evidence of bats or no potential for bats is found, then no further surveys are required and we will provide you with a letter based report to submit alongside your planning application.
The aim of the emergence/re-entry surveys is to observe and record bats emerging or re-entering from features identified during the preliminary roost assessment. Emergence and re-entry surveys can be carried out from May to September, following guidance from the Bat Conservation Trust Bat Surveys for Professional Ecologists: Good Practice Guidelines. If the building has high potential i.e bat evidence has been found or the building has multiple features suitable for roosting bats, then three surveys are required. Buildings with moderate suitability will require two surveys and buildings with low suitability will require one survey visit. Emergence surveys are undertaken 15 minutes before sunset and last for up to two hours after sunset, re-entry surveys start two hours before sunrise and last until sunrise or for 15 minutes after sunrise depending on the level of bat activity. The number of surveyors needed to carry out bat surveys will depend on the building size and number of features to be surveyed. Where sites are complex we utilise modern technology such as the use of thermal imagery, automated detectors and drones.
Although surveys can be undertaken between May and September, for buildings with low and moderate suitability, at least one survey has to be between May and August. Buildings with high suitability have to have two surveys between May and August. The levels of bat activity are highly dependent on weather, types of roost and season. It is best practice to spread bat surveys out across the survey period, this will allow us to detect and identify the different types of roosts present on site.
Once the survey has been completed we will provide you with a report which will contain the survey findings, analysis and recommendations on how to progress with the development.
More complex issues such as if the building offers hibernation potential will be discussed with you and additional surveys may be needed. Bat activity surveys may be recommended on larger sites where bat foraging and commuting is predicted.
Why do I have to do a bat survey?
A bat survey is required to provide information on the species of bat, type of bat roost and the features used by the roosting bats. We collate the information from across the bat survey season to then provide pragmatic mitigation proportionate to the roost type and the species present.
Bats are fully protected by both UK and European legislation. Therefore, where a bat roost is to be affected by a development then a Natural England, Natural Resources Wales or Scottish Natural Heritage licence will be required.
A licence to undertake works that may disturb or destroy a roost cannot be applied for until a full bat survey has been completed.
What if I have planning?
Although planning may have been granted, bat surveys may still be required. Planning permission does not override legislation and therefore there is still a legal requirement to ensure bats are not impacted by the new development.
If you have planning and the proposed development may risk bats or there is a condition for a bat survey the first stage is to appoint an ecologist to carry out a preliminary roost assessment.
Class Q permitted development
There are certain circumstances where planning permission is not required for the change of use of a building. Advise should be sought from an ecologist as early as possible.