Bat surveys

There are 17 resident breeding species of bat in the UK, varying in size from our two smallest and most common Pipistrelle bats (which can fit into a match-box) to our two largest bats, the noctule and the greater horseshoe.

Bats are typically found roosting in a variety of habitats including underground, trees, buildings and bridges. All UK bats feed on insects, although they each have subtly different diets and are therefore best observed foraging where insects are most abundant: primarily, waterbodies and woodland, gardens and parks, and along hedgerows and tree lines. Bats often use linear features within the landscape such as hedgerows to navigate.

Brown long-eared bat by Adrian Orrell

Brown long-eared bat by Adrian Orrell

The calendar year for a bat usually starts with hibernation and they only emerge in the spring as the weather ameliorates. In the early summer, females form maternity roosts where most give birth to a single pup, usually in June or July. Just a month or so later, the juveniles are volant (i.e. able to fly) and these roosts will then often begin to disperse.

Shortly after this, bats will begin to mate. Some species will head to communal ‘swarming’ sites, where mating and other social exchanges will occur between multiple bats on favourable nights through the autumn. Often these sites are then used for hibernation, which typically takes place in an undisturbed place with a cool climate where bats will significantly lower their metabolic rate. Bats use very little energy when undisturbed, although some will occasionally stir on milder nights, perhaps even to mate.

Bats are most vulnerable to harm if disturbed during hibernation or the maternity period. However, all bats and their roosts are protected from harm and disturbance at all times by EU and UK law. Bats’ foraging habitats also receive some protection within the planning system.

Protection for bats

For more information on bats and the law, visit the Bat Conservation Trust website.

Senior Ecologist, Matt Cook, uses an endoscope to survey for bats in a farm building on a film set. Photo by Ecologist, Courtenay Holden

Senior Ecologist, Matt Cook, uses an endoscope to survey for bats in a farm building on a film set. Photo by Ecologist, Courtenay Holden

Bat surveys: methods and times

Bats can typically be surveyed between April and October using a variety of different survey methods. At Baker Consultants, we use the most effective method for the objectives of the project and are guided primarily by the Bat Conservation Trust Bat Surveys Good Practice Guidelines,3rd Edition.

However, we also adhere to the Joint Nature Conservation Committee Bat Workers Manual, 3rd Edition (Mitchell-Jones, A.J., & McLeish, A.P. Ed., 2004), the English Nature (now Natural England) Bat Mitigation Guidelines (Mitchell-Jones, A.J., 2004) as well as up-to-date technical notes, professional guidance and scientific research.

Often, we are asked to carry out bat surveys of buildings or structures. This involves a preliminary (daytime) assessment, which can be undertaken at any time of year, although between spring and autumn is often preferable. On these surveys one of our Natural England-licensed bat ecologists will conduct a thorough external and internal search for evidence of the presence of roosting bats but also record features with the potential to support roosting bats, even if no evidence is actually identified.

Spectrogram showing a common pipistrelle bat call

Spectrogram showing a common pipistrelle bat call

If a building or structure is found to support bats, or their likely absence cannot reasonably be determined from the preliminary daytime assessment, then further nocturnal survey work is usually required. Dependent upon the level of any bat evidence identified, or the potential of the building to support bats, this will usually comprise one to three nocturnal survey visits where multiple surveyors are placed at vantage points to observe any bat activity associated with the building or structure at dusk or prior to dawn. These nocturnal surveys are preferably undertaken from May to August, although may extend to include April and September in certain circumstances and if suitable weather prevails.

Other bat surveys

Other frequent bat survey work we undertake include walked transects (see photo above) and the remote deployment of automated bat detectors. These survey methods, along with back tracking and more advanced survey techniques (mist nets, harp traps and acoustic lures) can be used to assess a wider site for the assemblages of bats present and how they might use its features. Typical examples the use of such surveys include informing housing or industrial developments and renewable energy installations.

We specialise in the deployment of automated full spectrum bat detectors and subsequent data analyses – read more here – and also have level 3 and 4 class licensed bat ecologists in-house.

Finally, where development might also impact upon trees and woodlands we can also undertake tree assessments via our qualified tree climbers, including using endoscopes, telescopic pole-mounted cameras and/or a suite of nocturnal surveys. Read more about tree assessments in our blog and watch the below video of our Technical Director, Carlos Abrahams, conducting a tree assessment, as filmed from his GoPro helmet camera.

Contact us now to discuss how our bat survey expertise can benefit your project