Bat Emergence Surveys
Dusk emergence, or dawn re-entry surveys for bats may be needed to determine whether or not bats are present within a building, and more importantly, to find out more about the bats using a particular building, including;
- Which species of bat are present
- How bats gain access to the building and what features they use
- The time of year bats use the building, and what they use it for (e.g. hibernation, nursery)
CEC undertake bat emergence surveys across Cornwall and Devon. Emergence or dawn surveys may also be required to determine whether or not trees are used by roosting bats, and the general methodology will be the same as that outlined below.
Bat emergence surveys will be designed for the site using the BCT bat survey good practice guidelines. As a general guide, to rule out the presence of bats at a site, 1 or 2 emergence surveys will be required and to work out more detail of how bats use the building will require 2 or more emergence surveys (surveys for either purpose may also be combined with remote monitoring). Emergence surveys can only be undertaken when bats are active, between May and September (inclusive). Where 2 surveys are required, they should be at least 4-6 weeks apart to see if there is any change in use.
Emergence surveys are undertaken at dusk, they normally start at about 15 minutes before sunset, and last for up to 2.5 hours or more. This ensures that the survey will pick up all species of bat – different species emerge from roosts at different times. The number of surveyors required needs to be determined on a case by case basis, but require enough people to be able to view every elevation of the building – so the more complex the building, the more surveyors will be required.
Dawn surveys start about 90 minutes before sunrise, and continue until shortly after sunrise. These surveys can be useful for pinpointing the exact access points used, because re-entry can often be easier to spot.
Surveyors will be visual searching the features of the building for bats emerging, and will use hand held bat detectors to pick up bat echolocation calls to aid identification.
The survey work will inform the design of any mitigation required, and this will be needed to inform both the planning application, and (if necessary) a European Protected Species (EPS) licence.
Emergence surveys may also be a condition of a licence application to monitor levels of bat use post construction.