Carrying out a bat survey is a multi-stage process and the amount of assessment needed depends on the initial evidence and the size and complexity of the structures involved.
Risk Assessment
The initial stage is a risk assessment survey where structure exteriors are visually assessed for potential access points and evidence of bat activity. Features such as small gaps in barge/soffit/fascia boards, raised or missing ridge tiles and gaps at gable ends, which have potential as access points are sought. Evidence that potential access points are actively used by bats includes staining within gaps and bat droppings or urine staining under gaps. Indicators that potential access points are likely to be inactive include the presence of cobwebs and general detritus within the access.
The interior of buildings are also visually assessed for evidence of bat activity and/or for potential to be used by bats. Evidence of a roost is determined as the presence of a dead or live bat, concentrated piles or scattered droppings, food remains such as insect wing fragments as well as scratch marks and/or staining.
Nocturnal Surveys
If a structure has the potential to support a bat roost then nocturnal surveys are undertaken to see if bats are currently present, what sort of roost it is, where all the access points are and how many bats are typically present. The number of further surveys required is based on the initial risk assessment given, which is usually between one and four.
These surveys are carried out during dusk or dawn to see bats leaving or entering the roost, and must be carried out by enough surveyors to see all sides of the building at all times. These surveyors are equipped with bat detectors to pick up their ultrasonic calls. These calls can help identify which species is present.