Surveyors count numbers of bats emerging from summer roosts at sunset on two evenings during the survey period. Surveyors choose their own roosts. A small number of counts are internal roost counts carried out under licence.
The NBMP Roost Count dataset includes records from a sample of summer roosts across the UK, and is not a complete record of all UK roosts. There are local gaps in coverage, and some sites have been excluded due to sensitivity issues.
Data are collected for the purposed of producing species population trends.
All data are collected using the same methodology. Species verification by BCT is an ongoing process and has not been carried out at all roosts, but in most cases identification is likely to have been carried out by an SNCO roost visitor or by the recorders themselves with the aid of a bat detector. The data do not provide a complete picture of bat roosts, but should be considered as a sample of roosts from across the UK. These data are not intended to replace systematic local surveys and data held by local records centres. The dataset has been checked using NBN Record Cleaner.
Surveyors stand outside exit points of known roosts in buildings and other structures, from approximately 15 minutes before sunset, and complete visual counts of bats as they emerge. A bat detector may also be used to help identify bats emerging and also verify species identification. The survey stops when: bats have finished emerging; it becomes too dark to see; bats are displaying confusing behaviour; or the weather conditions deteriorate dramatically.
Two surveys take place in June, and for pipistrelles and brown long-eared bats additional counts take place in July. Counts for lesser horseshoe bats take place in May/June and for greater horseshoe bats in July. Additional counts may take place in other months.
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Metadata last updated on 2017-06-16 14:28:46.0