A comparison of the precision of four common methods currently used to count bats emerging from summer maternity colony roosts in the UK.

1. Counting the number of bats emerging from a roost gives a good indication of how many individuals are using the structure at the time of survey. These emergence counts are a valuable survey technique and are used by ecological consultants to aid in the design and post-monitoring of mitigation if development work occurs. Therefore the survey methods used must be accurate if correct conservation measures are to be applied. 2. This experiment compared four common methods used by surveyors to determine how effective advanced technologies are for providing precise counts of roost numbers, in comparison to traditional visual observational surveys. Recommendations are made as to which survey type should be applied under various conditions. 3. Methods used were: a. A visual count b. A visual count using a heterodyne bat detector c. A visual count using a night vision scope d. A remote recording bat detector All four methods were run together for six of the UK bat species at six different roost locations. The species were Brandt’s bat Myotis brandtii, brown long-eared bat Plecotus auritus, Daubenton’s bat Myotis daubentonii, Leisler’s bat Nyctalus leislerii, lesser horseshoe bat Rhinolophus hipposideros and soprano pipistrelle bat Pipistrellus pygmaeus. 4. There was no significant difference between the four methods across all six bat species. There was a significant difference between methods for the brown long-eared and Daubenton’s bat roosts. There were no significant differences between methods for Brandt’s, Leisler’s, lesser horseshoes or soprano pipistrelles, although the numbers of bats observed emerging across the four methods were not consistent with each other. 5. Factors influencing which methods should be used during surveys include a. The entrance/exit hole b. The species of bat c. Activity around the roost Careful judgement should be used when deliberating which combination of methods and survey effort are required.Faculty of Science & Technolog