There are 18 species of bats in the UK and at least 13 of these species might take the opportunity (if the feature is suitable) to roost in a building.
Long ago, before people drastically altered the natural landscape, cutting down woodlands and building houses and other useful structures, bats used to live more frequently in trees and crevices in rocks and caves. Just as we have evolved to live in new places, so have they and now they take the opportunity to roost where suitable space is available.
Bats roost in buildings (they don’t nest) and they don’t build a nest with nesting material like other small mammals do - they are quite clean and non-destructive. They don’t chew and only spend part of the year in a roost sites, although that roost might be used regularly for many years. In fact, if there are bats in your house, you may not even know they are there.
Bat surveys of buildings are most often requested to support a planning application. If requested to undertake a bat survey of a building I would, in the first instance, make a visit to the site in order to undertake a daytime inspection; a preliminary roost assessment. As part of the inspection I would look for features in the building that might provide suitable roosting space.
Features might include lifted or cracked tiles, lifted flashing, hanging tiles, gaps under fascia boards and crevices in brickwork. Crevices-dwelling bat species, like pipistrelle species and whiskered bats (Myotis mystacinus) favour these sorts of places. In the right position, roof tiles can heat up nicely in the sun and the space between the tiles and the roof lining can provide a warm secure place for pipistrelle maternity roosts in the summer months.
During my inspection I would also look inside the building. If the building is inhabited, I might only inspect the loft space and cellar, but if it were partially open, for example a barn, I would inspect the entire interior to search for places bats might roost. These might comprise gaps in mortice joints in beams, crevices between beams and purlins, gaps behind boarding or wall-coverings and spaces behind ripped roofing felt. Some bat species like Natterer’s bat (Myotis natteri) and brown long-eared bat (Plecotus auritus) primarily roost in sites where there are large spaces in which to fly prior to leaving a roost and might be found in open buildings or in loft spaces.
During the inspection I would search for signs of bat presence, including bats themselves, dead bats, bat droppings, staining from urine or oil (from fur) on beams and walls and feeding remains.
Of course, there are many types of structure, from houses, industrial buildings, barns and churches to icehouses, stone walls, tunnels, viaducts, aqueducts and bridges, all of which provide different features that might be utilised by roosting bats. The strategy of survey for each one would differ.
However, it is not always possible to determine presence or absence of a roost, or the type of roost as a result of an initial bat survey inspection, and if that were the case I might recommend further bat survey work in the form of emergence and activity surveys, which are undertaken at dusk, or a re-entry survey in the early morning. These surveys allow us to determine if bats are emerging from, or re-entering a roost within a building or structure. They would also provide more information on the species present, the number of bats and the type of roost.
A daytime bat survey inspection of a building can provide a lot of very useful information, but all site visits are different and it requires skill to interpret the results accurately.
There are different types of bat roosts that might be in a building, including maternity roosts, summer day and night roosts, transitional roosts, satellite roosts and hibernation roosts. Maternity roosts are those in which the female bats of a species congregate together in the spring to have their young and nurse them through the summer months. For this reason they are the most important type of roost, critical to the stability of the population in an area. In some cases maternity roosts can be very large – one of the largest soprano pipistrelle (Pipistrellus pygmaeus) roosts I have seen included over 300 female bats!
Bats might also only use a building temporarily, say, for one or two nights in order to rest, or for a period of weeks. Buildings and structures can also be used in the winter months as hibernation roosts. Hibernation sites have different qualities to summer roost sites and places that provide a more constant, cool, stable temperature, such as ice houses, tunnels, cellars and old war bunkers might be more favourable. If such a structure exists and appears suitable for bats, it may be necessary to undertake a winter bat survey inspection to determine whether or not it is used.
Bat surveys are most frequently undertaken as a result of the planning system. If work is to be undertaken to a building or structure that might support a bat roost, it is necessary to undertake survey work to determine presence or absence.
It is best to get bat survey work done before applying for planning permission as submission without the correct, up-to-date survey work can cause delays and increases in cost.
Even if surveys are not a requirement of planning, it is important to take into account the possible presence of bats in buildings.
Individuals as well as companies have an obligation under the UK and EU legislation to ensure that there is no disturbance or harm to bats or their roosts, so if you are having roof work done that does not require planning, it is important take the possible presence of bats into account. If you don’t, and bats are found during works, it could result in possible prosecution as well as causing delays and increased expense.
Although dusk and dawn emergence / re-entry and activity surveys can only be undertaken at a time when bats are active and present in the roosts (May – August), preliminary bat inspections of buildings and structures can be undertaken at any time of the year.
If a bat roost is found present in a building, and if proposed works might result in disturbance or destruction of a roost, or disturbance or harm to bats, it will be necessary to apply for a European Protected Species Mitigation (EPSM) licence from Natural England before starting the work. The process of applying for a licence would involve undertaking robust survey work (a roost characterisation survey) at the correct time of year and provision of suitable mitigation measures.
Bats and their roosts are protected under UK law (the Wildlife and Countryside Act, 1981, as amended) and EU law (the Habitats Regulations 2010).
Useful reference: Hundt L (2012) Bat Surveys: Good Practice Guidelines, 2nd edition, Bat Conservation Trust
If you would like a Bat Survey, an Ecological Appraisal (or Phase 1 Survey), or a survey specific to another Protected Species - or even if you are just after some advice, don’t hesitate to give us a call on 07917 852401 or send us an email.
News / Blogs
January 2019: We have relaunched the Verity Webster Ltd website with some exciting new elements.... >>
February 2017: Verity Webster discusses conducting ecology surveys through the seasons... >>
December 2015: Verity Webster discusses badgers, badger setts and mitigation issues... >>
August 2015: Verity Webster discusses bats, buildings and bat surveys... >>
June 2015: Verity Webster discusses the Himalayan Balsam, a non-native Invasive Plant Species... >>