Common Bat Survey Questions


Bats are protected under EU and UK law meaning that if you have a bat roosting within your property or if the county ecologist has flagged your property up to be in an area good for bats, then you will have to apply for a European Protected Species Licence (EPS). This allows you to gain permission to conduct your development. To get an EPS licence, you need to have your property assessed for bats by a professional ecologist.

The ecologist will then produce a report for you to submit to the planning authority, once this is approved you will need to apply for an EPS licence, this will be approved by Natural England/Natural Resources Wales. The licence is a break down of the report originally issued to the client and will then allow you to start your development works and is a legal document allowing you to do so. If you destroy a bat roost to build a development without a licence you are committing a crime.

The assessment for bats conducted by the ecologist is often in two phases.

Horseshoe bat
Lesser horseshoe bats roosting

The first phase is a preliminary roost assessment, where an ecologist will look at the external features of your property and any loft or attic spaces internally looking for potential and evidence of bats. If the property has potential and/or evidence of bats living there then the second phase is bat activity surveys.

Bat activity surveys can comprise either transects and remote monitoring for areas of land with potential for foraging and commuting, or dusk emergence/dawn re-entry surveys for properties/trees.

  • The dusk emergence/dawn re-entry surveys are where a number of surveyors (depending on the size of the property) will record bats emerging from your property (a dusk survey) or re-entering the property (a dawn survey). The maximum number of dusk/dawn surveys that can be required is usually three. It is recommended that at least one of these should be during the bat maternity season in mid-June/mid-July where there is a possibility of a maternity bat roost.
  • Transect surveys are where surveyors walk around the site at night with a bat detector and record all bats they observe. In addition to this, some bat detectors will be left securely on site for remote monitoring to record for a minimum of 5 nights of good weather. These surveys take place between April and October, and the frequency of surveys during these months depends on how important the site is predicted to be for bats.


A preliminary roost assessment is ONLY looking for potential or evidence of bats, even if droppings or actual bats are found. This stage can usually be done in a few hours or in a day depending on the size of the development.

St Tewdrics - fresh LHS droppings in bat loft

To apply for the EPS licence, you need to know the exact numbers and species that are potentially roosting within your property. However, it is difficult – if not impossible – to find out this information during the preliminary roost assessment. The bat activity surveys allow this to be recorded – ecologists will use bat detectors to identify species flying out of the property/tree, observe where the roosting locations are and any vital commuting and foraging routes that they may use in that area.


Preliminary roost assessments can be conducted at any time of year. It is during this phase that the ecologist can assess whether the developer needs further surveys, how many they need and how many surveyors will be needed to meet the guideline requirements. Activity surveys cannot be conducted at the same time as we need to know the exact numbers of surveys and surveyors needed so as that we can provide an accurate cost to our client. Activity surveys are seasonal; this is because bats hibernate during the other months and are not active. Why not check out our Ecological Survey Calendar to see what surveys can be undertaken throughout the year?


Bats can enter a crevice that is about the size of your little finger.

Many people get confused when an ecologist says that they found no bats, no evidence of bats in the form of droppings or feeding remains but that the client needs further surveys due to the property having potential. Bats have many different types of roosts. These are not used all year round – different species of bats have different roosting requirements meaning that just because a bat is not utilising the building at that point in time, it does not mean that they do not use the building as a roost in the summer, or in the winter, or at any point in the future.

An ecologist will record any crevices, raised tiles, raised fascias, barge boards, lead flashing, any features that a bat can squeeze into. However, they may not be able to physically inspect every feature for evidence.

So further surveys are needed to know exactly what species are using the building, where they are roosting and how many are there. This is to allow for the development to not have any negative impacts to the bats during the development and for appropriate mitigation to be put in place for the bat species living there.


Dusk emergence and Dawn re-entry surveys

If your property needs further surveys it will be in the form of dusk and dawn surveys, these are where surveyors will stand outside your property and record any bats emerging, entering and interacting close to the building, 30 minutes before sunset or 2 hours before sunrise depending on the species thought to be there. Any foraging and commuting routes nearby will also be recorded. How many surveyors are needed are decided during the preliminary roost assessment.

Your property will be assessed during the preliminary roost assessment using the following categories:


What this means


Negligible No access points for bats and/or nowhere suitable for bats to roost.No further surveys.
LowA low number of crevices or features where bats could roost. Features are not ideal but likely to be used occasionally in the summer. One further survey.
ModerateA moderate number of crevices or features bats can roost. Likely to be used on a regular basis in the summer. Two further surveys.
HighA high number of crevices or features bats can roost on a regular basis. Potential to support a maternity roost.Three further surveys. One of which needs to be conducted during the maternity season between mid-June to mid-July.

Please note that these surveys would need to be spaced a minimum of two weeks apart. However, it is recommended that the spacing between surveys is one month apart as this will usually produce better results – and some planning authorities ask for this too!

Transect and Remote Monitoring Surveys

If your land needs further surveys, it will be transect surveys and remote monitoring that would be recommended as a result of the PEA survey. Transect surveys usually commence at/before sunset and last for 2-3 hours and occur between April and October. Bat detectors deployed for remote monitoring will be left out to record for at least 5 nights of good weather.

Your land will be assessed during the preliminary ecological assessment using the following categories:


What this Means


NegligibleFeatures present not likely to be used by batsNo further surveys needed.
LowCould be used by small numbers of bats, but isn’t well connected to surrounding landscape.One transect and one remote monitoring survey (1+ detectors) per season (April/May, then June/July/August, then September/October).
ModerateContinuous habitat connected to the wider landscape that could be used by commuting bats.One transect and one remote monitoring survey (2+ detectors) per month. At least one transect should comprise a dusk and pre-dawn survey within one 24-hour period.
HighContinuous, high-quality habitat that is well connected to the wider landscape. Likely to be used regularly by bats. Site is close to and connected to known roosts.Two transects and two remote monitoring surveys (3+ detectors). At least one transect should comprise a dusk and pre-dawn survey within one 24-hour period.

These activity surveys allow surveyors to identify the species, the roost location and the number of bats roosting there. This information is vital and the client will need this to apply for an EPS licence and for it to be approved by Natural England/ Natural Resources Wales.

WARNING – if you need a bat survey and have found this out towards the end of the activity survey season (September), PLEASE BE AWARE that you may have to wait until the following year for the activity surveys. By getting the first phase done early, booking in your further surveys at the start of the year, being aware of timings, and how this might delay your development is vital. Wildlife is seasonal – they do not abide by our rules!

We will always try to do our utmost to make you, the client happy, however, we must abide by strict wildlife survey guidelines which means we can do our jobs accurately and beyond reproach. If we are unable to do a survey or have suggested further surveys it is not because we want to cause you difficulties, it is because we know that the local planning authority and Natural England/Natural Resources Wales will not accept the report or licence if it is applied for without further surveys, delaying works further. We could also lose our licences to do bat surveys and our jobs if we go against these guidelines.

We want to help both you, the client and the wildlife, as we have both your interests at heart.


If no bats are found during the further surveys and no evidence was found during the first phase then you do not need to apply for an EPS licence. Precautionary measures will be put in place, and enhancement measures will be suggested to make the development attractive for bats once it is complete.


Acer Ecology Report

Ten working days after the preliminary roost assessment has been conducted, once you have the report you can then ask us for a quote for the further surveys, if needed. At this stage, you are also able to ask other ecological consultancies for quotes for further survey work.

The activity surveys can take a few months to complete due to the methodology that we have to abide by, however, the report will be issued to the client ten working days after the final survey has been completed. For large/complex projects, it may take longer to agree a mitigation strategy between us (the ecologist), the architect, and the landowner. Sometimes, it is appropriate to correspond with the LPA and NRW/NE for input on the strategy to ensure that the proposal will pass through planning as this will prevent more costly delays further down the line.


The cost of a preliminary roost assessment is dependent on how far away the site is from our offices and the size and complexity of the site.


This is a little more complicated, the size of the property will dictate how many surveyors are needed, and the potential for bats and or the evidence found will dictate how many surveys are needed.

Bat Survey High Wycombe

However, if droppings are found, they may be required to be sent off for DNA analysis if bats are observed during the second phase but were not able to be identified. This is a further cost as well as the bat sound analysis and then report costing on top of this. The location can also add an extra cost due to mileage. Every property is different and there will be a different scenario for every client – this is why the first phase is so important and should not be undertaken at the same time as the further surveys to avoid charging the client more than is needed.


We hope that this answers the majority of your questions, but if you have any further queries you may have please do not hesitate to email us on

If you would like to find out more about Bat Surveys, or if you think you need a bat survey:

If you would like to read more on our Common Questions series, check out these blogs: