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What Happens on a Bat Survey?

Information for Homeowners who need further surveys to determine the presence or likely absence of bats to aid their planning application.

If your project has been assessed during an initial Preliminary Roost Assessment to have any potential for roosting bats then your property will need additional surveys to fully understand how bats are using the roost and to determine what mitigation needs to be put in place for you to be able to complete the required works and/or submit your plans to the Local Planning Authority.

This additional survey work is referred to as a ‘bat emergence/re-entry survey’, which comprises a combination of visits to the property at night and early in the morning. During these visits, the exterior of the building is watched for signs of bats emerging or re-entering. If bat droppings have been found during the search of the building, then these will also be sent to a laboratory for DNA analysis to help identify the bat species present.

If your property has been assessed for roosting bats as having:

High potential (or bat droppings found) - x3 survey visits will need to be completed.

Medium potential - x2 survey visits will need to be completed.

Low potential - x1 survey visit will need to be completed.

Please note that if any bat is seen emerging or re-entering the property on a medium or low potential property then this will mean further surveys are required.

What to expect during a bat emergence/re-entry survey

The time when a bat emergence/re-entry survey can be undertaken is determined by the ecology of the species. The surveys can only be conducted within the months of May – September because this is when the bats are most active. The months of June – August is the main period for births and young bats in the roost, and survey during this period would identify important maternity roosts, which have a higher mitigation requirement. Where multiple survey visits are required, these need to be sufficiently spread throughout the survey period to ensure an accurate assessment of the building.


The weather is a major influencing factor on whether an individual survey visit can go ahead – we do everything possible to keep to our scheduled dates but we have to keep to the guidelines that are set out by the Bat Conservation Trust. Temperature, wind speed and precipitation must be taken into account during a survey as all these factors influence whether bats will be foraging outside of their roosts. We follow these guidelines to ensure good practice; which means the survey data collected will be considered valid by the relevant authorities. If surveys are undertaken when the conditions are not optimum, this will not be considered as typical behaviour and risks being rejected. Therefore, it is because the weather conditions affect the bats behaviour that means we have to cancel a survey visit…. not because our surveyors do not like the cold and rain! However, we do understand that this can be very frustrating for you if we have to continually reschedule your surveys because of the weather, but unfortunately this is out of our control, so please be patient with us.

Typically, we will book the first survey visit in with you and then after that we will be in touch to arrange the next date for the following survey visits, if required.


Our team will generally arrive at your property 30 minutes before sunset for emergence survey visits and 2 hours before sunrise if you need a re-entry survey visit. These timings are all prepared beforehand and you will be informed of the timings before we arrive. We do not need you to be awake or available for the survey to be conducted, however, we do need suitable access to gain entry onto the grounds of the property and so will ask that you leave any gates unlocked or give us instructions on how to gain access into the property before we arrive so that we keep the disruption to you at a minimum.

The amount of surveyors and their positions over your property will be assessed and decided prior to commencing the survey. We will therefore contact you before your survey to let you know how many surveyors and how many night vision cameras will be used during the survey. Please note that any cameras that are used will only be positioned to capture the activity of the bats – no cameras will be positioned in a way that invades the privacy of the home owner. We have a dedicated Data Protection policy in place to protect you here.


At enims we provide a text service where we will keep you updated on the possibility of the cancelation of the survey due to weather and if we deem it really necessary to

cancel at the last minute this proves an effective way of letting you know. Also we use our text service to gently remind you that your survey will be conducted on that evening or morning so you are aware that we are coming. Within this text message we will inform you of who the lead surveyor is and the time that the team will be turning up to conduct the survey. Please click here if you haven't already signed up for this service.


Once the full suite of surveys have been completed, we will analyse all the data that we have collected from the each surveyor, night vision camera footage and the results from any DNA analysis of bat droppings. Our experienced ecologists will then write a report based on all the findings; setting out any further survey needed (some buildings may require a hibernation survey during the winter months) and recommendations for any necessary mitigation. The time to put the report together will be based on the individual property and the complexity of the findings; i.e. what, if any, evidence of bats, the species, number and what type of roosts are present. We will always keep you updated on the progress and please be assured that we do everything we can to get the reports over to you as swiftly as we possibly can.


The above outlines a typical process. If you have a more complex development this may require different approaches which you will be fully informed about.

We are always happy to talk you through any aspect of the survey that you are unsure of or wish to clarify. Please contact us here if you need to or ring us on 0845 6440196.

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