Hibernation
Surveys
Bats can hibernate at any time between November and March with a core hibernation period typically being between December and February, waking only occasionally to feed on warm nights.
Bat hibernation surveys may be required if your project is ‘reasonably likely’ to impact a structure or tree that could subsequently impact bats and their roosts during the bat hibernation period.
Bat hibernation surveys are normally undertaken at the planning stage of a development and they are commonly requested by Local Planning Authorities to support planning applications. For developments not requiring planning consent, hibernation surveys for bats should be undertaken at the design stage of the project.
Where do bats hibernate?
Bats use structures (such as churches, houses and bridges), underground structures and trees to hibernate that provide stable and cool conditions for bats.
Bats will frequently use the same roosting sites throughout the year and this can be a good indicator that bats are using a feature to hibernate.
What you need to know about bat hibernation surveys
How to know if you need a bat hibernation survey
The need for a hibernation survey and the number of surveys required is determined by a suitability category assigned in a Preliminary Roost Assessment (PRA) of a structure and a preliminary ground level tree roost assessment (PGLTRA) for trees.
You may also be informed by your Local Planning Authority if a bat hibernation survey is likely to be required for your project as part of a planning application or listed building consent.
What does a bat hibernation survey involve?
A systematic inspection of any cracks, crevices or voids for hibernating bats is undertaken at the structure or tree in question. Automated bat roost loggers are also used where possible to detect the presence of hibernating bats by recording their echolocation or social calls.
The survey effort required is determined by the suitability category assigned during the PRA and PGLTRA survey as summarised below:
- A minimum of two survey visits are normally required to be undertaken in mid-January and in mid-February if the counting of hibernating bats is required
- Three surveys could be required for buildings classified as having moderate or high suitability for bats during a PRA or PGLTRA, with one survey completed in each month between December and February
Buildings classified as moderate or high suitability for bats could also require automated/static surveys using automated bat detectors to monitor bat activity for two weeks in each month for December, January and February.
Our approach
At Arun Ecology, our bat hibernation surveys are carried out in accordance with the Bat Conservation Trust’s good practice guidelines for surveying bats. This is the standard methodology expected by Local Planning Authorities (LPAs) and regulators such as Natural England.
We have in-house specialist bat ecologists who are registered to use the Level 2 Class Licence to Survey Bats – the required credentials to survey hibernating bats.
What next following a bat hibernation survey?
Scenario 1 – If bats are recorded during the bat hibernation survey then a mitigation licence will need to be obtained from the regulatory body from Natural England for the project to proceed lawfully. Further bat dusk emergence and dawn re-entry surveys could also be required to characterise the bat roost in the active season for bats.
Scenario 2 – If no bats are recorded during the bat hibernation surveys, and they meet industry best practice guidelines, then the report provided by Arun Ecology can be used as evidence that hibernating bats were likely absent at the time of the surveys.
It is important to note that a standalone bat hibernation survey is unlikely to be enough to obtain planning consent. Further bat dusk emergence and dawn re-entry surveys would be required to determine if bats are using the structure or tree during their active period to demonstrate a proportionate survey effort to determine presence/absence.
FAQs
It is possible that planning permission could be refused without a bat hibernation survey being undertaken if a tree is assessed as being suitable to support hibernating bats is reasonably likely to be impacted by the proposals.
In certain circumstances it may be possible to justify that hibernating bats will not be impacted by the proposed works and that bat hibernation surveys would not be appropriate by altering the project design or timing of works.
It may be possible to undertake your proposals during the winter months if you have taken appropriate care to demonstrate that hibernating bats would not be impacted. This might include undertaking a Preliminary Roost Assessment or Preliminary Ground Level Tree Roost Assessment to determine the suitability of the building for hibernating bats. It could also include undertaking targeted surveys to determine presence/likely absence of hibernating bats.
Ideally, projects should try to schedule works to avoid the bat hibernation period in case a hibernating bat is discovered during works. If bats are discovered it is likely that a European Protected Species Licence (EPSL) would be required to proceed lawfully.
Natural England may include conditions within the EPSL that could delay works until the end of the sensitive hibernation period for bats.
The suitability of a structure to support hibernating bats and recommendations for hibernation surveys are usually outlined in a Preliminary Roost Assessment or, in the case of a tree, a Preliminary Ground Level Tree Roost Assessment.
In the UK bats typically hibernate between the months of November and March, surviving predominantly on body fats built up, waking only occasionally to move within their roosts or forage on warmer nights. The length of the hibernation period can vary between species and is temperature dependent so may start later or end earlier.
Bats typically hibernate in places that have stable and cool conditions and that are likely to remain relatively undisturbed between November and March. This can include underground caves and mines, trees and many types of structures.
The reality is that bat ecologists are still learning where UK bats hibernate. For example, in the case of Britain’s most common bat, the common pipistrelle, not enough hibernation roosts have been found to account for the numbers of common pipistrelles recorded in the summer. Recent research has shown that roosts detected in the summer and swarming sites used in the autumn can often be used for hibernation, although not always for the same bat species.
If you come across a hibernating bat during your works you should stop works. It is likely that you will need to apply for a European Protected Species Licence to proceed lawfully. Bats are protected from killing, injuring and disturbance in their breeding and resting places. It is particularly important that the bat is not woken as the energy used to wake up could result in the bat not being able to survive on its remaining fat stores through the winter.
Helping to address the ecological
and climate crisis
At Arun Ecology it’s not all just about driving business. We want to contribute to addressing the challenges of our time to ensure a prosperous future for the next generation.
So, as part of our service, each time you commission us we are committed to planting one tree within the UK, through our partnership with Creating Tomorrow’s Forests.
Watch this space to find out more about how we are contributing to nature recovery and tackling climate change.
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