Bat Surveys

Bat surveys are required if there is a reasonable likelihood of bats being present in the location of a planned development, as local authorities are obliged to ensure the conservation of biodiversity – such as bats and other protected species – under the European Habitats Directive.

Bat surveys usually fall into two stages - a visual survey and an emergence survey.

A bat visual survey involves a site inspection whereby an ecologist will gain access into all of the internal voids, attics, and basements of the building to search for evidence of bats. The exterior of the building is also assessed for potential roosting sites and access points. Bat surveys of trees are mainly carried out from ground level and low-level ladders with the aid of binoculars. Surveys mainly focus on assessing the potential of the site to support bats.

A bat emergence/re-entry survey will be required if the site is deemed to have potential for bats. It requires two or more trained bat specialists stationed around the building, in locations that allow all potential access points to be observed. They use bat detectors in order to identify species of bat present. This type of bat survey takes place at either dusk or dawn. Dusk surveys usually starts around 15 minutes before sunset and depending on the species of bat thought to be present, may continue for up to 2 hours. Dawn surveys start 1.5 hours before sunrise until 30 minutes after. Usually two or three surveys will be required.

Bat emergence surveys are usually carried out between May and September when bats are active and not hibernating.

If a proposed development will affect a bat roost, a European Protected Species Licence may be needed prior to the start of works. The licence application process requires the agreement of a method statement which will ensure that bats can continue to occupy the site after the development has been completed through mitigation strategies.