Bats are a frequent consideration when it comes to development projects. In this article we take a tour of bat surveys and bat ecology.

All bat species and their roosts are protected by law; legislation makes it an offence to destroy, damage or block access to a bat roost, or to deliberately or recklessly disturb, injure or kill any bat. The roost is protected whether bats are present or not.

Bats are generally active at night and utilise a wide range of habitats for foraging and commuting between roost sites, hibernation sites and foraging habitats. Linear features such as hedgerows, woodland edges and even fences can be important for navigation between roosting and foraging habitats.

Bats have seen significant declines over the last century and are still vulnerable to threats such as habitat fragmentation and habitat loss.

Bat ecology

At this time of year, bats focus on building fat reserves, seeking out hibernation sites, and mating. During periods of cold weather, bats will enter torpor and as temperatures continue to drop over the coming weeks, they will go into hibernation – lowering body temperature and metabolic rate to conserve energy whilst they live on fat reserves. They will occasionally emerge to feed during the winter months if temperatures are warm enough.

In March/April, as temperatures warm, bats begin to emerge from hibernation more frequently. Bats are fully active by May; females form maternity roosts, ready for the arrival of pups in June and males roost on their own or in small groups. Over July, the females continue to raise young bats, which can fly and feed independently by August when maternity colonies begin to disperse. In September, the mating season begins, which brings us full circle.

Bat surveys

An initial bat scoping survey identifies suitable features within a site and its surrounds that may be used by bats for roosting purposes, assesses the need for further surveys, and the likely impacts of a proposed development project on bats. Habitats within and surrounding the site are also assessed for their potential to support bat activity. Scoping surveys can be undertaken throughout the year.

Following on from a scoping assessment further survey work may be needed where features are identified as a confirmed bat roost or a potential bat roost.

Emergence/re-entry surveys seek to confirm presence/likely absence of bats and/or characterise the type of roost that is present, species of bat and numbers. Emergence/re-entry surveys take place at dusk (and dawn) and typically comprise surveyors observing all potential roost features, in addition to deploying cameras and static bat detectors. Bats seen to emerge from, or re-enter, potential roost features during the survey are recorded, along with general bat activity and behaviour.

If a bat roost is confirmed, a licence may be required for development works to go ahead.

A bat activity survey focuses on suitable features that may be used by bats for foraging/commuting/dispersal purposes. Surveys typically involve surveyors walking predetermined transects or recording activity from vantage points, the use of cameras to record activity overnight, and the use of static detectors to record bat activity over a set period.

Bat emergence/re-entry surveys and activity surveys are seasonally restricted. Optimum months are between May and August.

Where further survey work is required to identify whether bats are using a potential hibernation roost, methods such as the deployment of automated/static bat detectors and specialist cameras can be set up and left in situ to record any activity.

Please contact us with any bat-related queries and our experienced ecologists will be happy to assist.