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.
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
- In England and Wales, the main legislation pertaining to bats and development is the Conservation of Habitats and Species Regulations (2010) where bats are European Protected Species. However, bats are also protected by the Wildlife and Countryside Act (1981) (as amended), the Countryside and Rights of Way Act (2000) and the Natural Environment and Rural Communities Act (2006).
- In Scotland, the key legislation that applies to bats is the Conservation (Natural Habitats &c.) Regulations 1994 (as amended).
- In Northern Ireland, bats are listed under Schedule 2 of the Conservation (Natural Habitats etc) Regulations (Northern Ireland) 1995 and, in the Republic of Ireland, under Schedule 5 of the Wildlife Act (1976) and Schedule 1 of the European Communities (Natural Habitats) Regulations, 1997.
For more information on bats and the law, visit the Bat Conservation Trust website.
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.
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.
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.