Bats are highly specialised animals with some amazing features. They are the only true flying mammals and are long-lived, intelligent, and have complex social lives. There are at least nine species in Scotland, of which the most numerous and familiar are pipistrelles, which can be seen flitting about near woodland or open water at dusk, in search of midges and other flying insects. A single pipistrelle can consume up to 3,000 midges in one night!
Bats are essentially woodland animals, but as the availability of natural roosting sites in trees has declined and the number of warm, dry alternative sites in buildings has increased, so have these artificial sites become very important for many species. They have well established traditions and tend to return to the same sites, at the same time, year after year. If bats are present during the summer, it is often possible to see them fly out at dusk or even hear them inside the roost on hot days or before they emerge in the evening. Frequently, though, only signs of bats will be seen rather than the animals themselves. The most characteristic signs are their droppings which are composed of the indigestible remains of their insect prey.
These are roughly the size and shape of mouse droppings but they crumble to a powder when dry and are usually found stuck to walls or in small piles below roosting bats or below the roost exit. There are three main types of roost:
- Buildings such as houses, churches, bridges, fortifications, schools etc. These are most important in summer, though some are used throughout the year.
- Caves, mines, cellars, ice-houses and tunnels. These are most important for hibernation as they give the sheltered and stable conditions that bats need during winter.
- Tree holes – used throughout the year.
An overview of the biology of the Scottish bat species can be found here.
- 1 How to get to know bats
- 2 Threats to bats
- 3 What you can do for bats
- 4 What’s special about bats?
- 5 Bats and the law
- 6 Scottish bats and their roosts
- 7 Bats in houses
- 8 Helping bats and getting involved
- 9 Needing help?
- 10 Advice for planners and developers
- 11 Mitigation
How to get to know bats
Bats occur throughout Scotland, including many of the islands, although in Shetland they occur as vagrants only. In general, north of the Central Belt, the number of bat species living in an area decreases the further north and west you travel. The south of Scotland supports the greatest number of different species. Some are much rarer in Scotland than others, notably noctules, Leisler’s, and whiskered bats which are all rare and have restricted ranges.
You can get a bat detector which makes the calls of your local bats audible to you and enables you to identify them. Your local bat group will help you obtain the best device and interpret the calls. They will also be pleased to hear about what you find in your area.
You should not handle bats if you are not properly trained – your local group can help with that too.
Threats to bats
Throughout Europe bats suffered a terrible decline in numbers during the 20th century, particularly since the 1960’s with some species becoming locally extinct. As a result of these threats bats and their roosts are now strongly protected by law.
The reasons for the declines are likely to include: loss of suitable roosts, loss of foraging habitat, reduced availability of insect prey through the widespread use of pesticides in the countryside, and direct mortality of bats caused by the use of highly toxic timber treatment chemicals in house roosts. The use of approved, less-toxic compounds has significantly reduced the last threat in recent years.
What you can do for bats
You can buy or build bat boxes to encourage bats. These days many bats breed in our attics (because they are warm and dry). Please do not disturb them if that happens to you. Because they share our homes mainly to breed, they will vanish again in August or September. If they cause a problem, your local Scottish Natural Heritage office can provide advice.
Local bat groups have a vital role in the conservation process in Scotland. So if you want to help bats, get in touch with the Bat Conservation Trust (Scotland) or your local group.
What’s special about bats?
Bats are highly specialised and remarkable animals with some amazing features. Like us, they are long-lived, intelligent and have complex social lives. Nine or ten species occur regularly in Scotland, but in recent decades the number of bats has declined significantly. Although we don’t have much historical information, it’s clear that many of our bats are under threat
Bats have a highly sophisticated echolocation system that allows them to catch tiny insects and avoid obstacles, even in complete darkness. A single bat may consume over 3000 midges in one night! When they’re flying, bats produce a stream of high-pitched squeaks and listen to the echoes to produce a sound picture of their surroundings. These ultrasound calls are too high-pitched for us to hear, but bat enthusiasts use electronic bat-detectors to convert them into audible sounds that can be used to identify the different species in the field.
There are very few insects around in winter, so all British bats hibernate. As the weather gets colder in the autumn, they become torpid, i.e they allow their body temperature to drop close to that of their surroundings, thereby allowing their food reserves to last much longer.
Bats and the law
All bats and their roosts are legally protected in Scotland by the Conservation (Natural Habitats, &c.;) Regulations 1994 (as amended) – “the Habitats Regulations”. For details of this protection, see Protected mammals – Bats and Regulations 39-41 and 44-46 of the Habitats Regulations.
A bat roost is any structure or place which a bat or group of bats use for shelter or protection. Because bats return to the same places every year, a bat roost is protected even if there are no bats there.
Some activities affecting bats or their roosts may need to be done in accordance with the terms of a licence. Licences allow certain illegal actions to be undertaken legitimately. Such activities might include:
- blocking, filling, or installing grilles over old mines or tunnels
- building, alteration or maintenance work
- getting rid of unwanted bat colonies
- removing hollow trees
- remedial timber treatment
- rewiring or plumbing in roofs
- treatment of wasps, bees or cluster flies
Without a licence, you may:
- tend a disabled bat and kill a seriously injured one
- remove bats from within the living area of a house.
Scottish bats and their roosts
Bats in Scotland
Bats occur throughout Scotland, including many of the islands. In Shetland they occur as vagrants only. In general, north of the Central Belt, the number of bat species living in an area decreases the further north and west you travel. The south of Scotland supports the greatest number of different bat species. Information on the current recorded distribution of all Scottish bat species can be found on the National Biodiversity Network (NBN) .
A bat’s choice of roost depends upon, amongst other things, its species and sex, the time of the year and the availability of food. In any one year several different roosts are used on a seasonal basis, where conditions meet the bats’ social and reproductive requirements at the time. Most bats form social groups for at least part of the year and it is at these times that bat roosts are most obvious.
Adult females gather together in maternity roosts in late May to early June to give birth and rear their babies. As soon as the young start to fly these maternity colonies begin to break up and the bats move to other roosts. Bats may congregate from a large area to form these colonies, so any major disruption at this summer breeding site could potentially wipe out all the females from the area. In contrast, male bats typically prefer to live alone or in small groups in cooler sites. During late summer male bats set up territories around a mating roost, to which they attract females.
There are three main types of roost:
- Buildings such as houses, churches, farms, bridges, ancient monuments, fortifications, schools, hospitals and all sorts of industrial buildings. These are most important in summer, though some are used throughout the year.
- Underground places such as caves, mines, cellars, ice-houses and tunnels. These are most important for hibernation as they give the cool, sheltered and stable conditions that bats need during winter.
- Tree holes – these are used by bats throughout the year.
Exceptional bat roosts
The vast majority of Scottish bat roosts comprise the two widespread pipistrelle species. Maternity roosts of these species commonly comprise around 100-200 adult females (common pipistrelle colonies tend to be smaller than those of soprano pipistrelles). But how do we know if a bat roost is exceptional, either by virtue of the species present or the sheer number of bats? The following would be considered as exceptional:
- Any roost comprising noctules, Leisler’s bats, whiskered/Brandt’s bats or Nathusius’s pipistrelles
- Exceptionally large roosts of any of the other five widespread species
- Roosts of any species at the edge of its UK or European distribution
With respect to the second bullet above, as a rough guide, the following colony sizes for the five widespread species would be considered exceptional in Scotland:
- Soprano pipistrelle >800
- Common pipistrelle >200
- Daubenton’s bat >80
- Brown long-eared bat >50
- Natterer’s bat >50
Where’s the best site in Scotland for bats?
Currently, the two best locations, in terms of species-richness, are both NTS properties in the south west of Scotland – at Threave and Culzean . The former is known to support at least seven species, including roosts of two Scottish rarities – noctule and whiskered bat. The latter supports eight species, i.e all but one of the nine species that regularly occur in Scotland.
Bats in houses
Like house martins and swallows, bats are usually seasonal visitors to houses and are typically present for only four to five months of the year. They tend to form maternity colonies during May and June and then leave during August and early September once the young bats are independent. The colonies are often most obvious during July, when the young are starting to fly; soon after this the adults will start to leave, followed by the young. Although this seasonal pattern usually applies, there are exceptions and sometimes bats can be found using the same buildings in both winter and summer.
To maximise warmth, maternity roosts are often located on the south and west of houses or close to sources of heat such as chimneys and boilers. Most species prefer to roost in quite small spaces and are not usually found in open draughty areas. The common and soprano pipistrelles are our smallest and most common bat species. They are generally found in the inaccessible parts of the roof structure and around its edges and rarely enter the loft space. Both species colonise new buildings quite readily and frequently roost in houses built since the 1960s. By contrast, the brown long-eared bat prefers older buildings with large roof spaces and is often seen in clusters at the top of the roof ridge inside the loft. Where bats are seen in buildings during the winter, they tend to be alone or in small scattered groups, hidden in crevices or under slates and away from sources of heat.
Bat colonies usually live happily with their human landlords, but occasionally problems or concerns arise. Scottish Natural Heritage is happy to provide advice on how to deal with any problems. See Needing help?
Helping bats and getting involved
Here are some ways in which people can give bats a helping hand.
Many bats rely on underground sites such as caves, abandoned mines, tunnels, cellars and ice-houses for hibernation. Unfortunately, such places are sometimes blocked up for safety reasons or by rubbish dumping, so bats either lose their hibernation site or, worse still, are sealed up inside. If you’re planning to block, cap, grille or demolish any sort of underground place which might be used by bats, please consult Scottish Natural Heritage before starting work. Also, try to avoid entering these places during the winter if you think bats may be hibernating there.
These are important for bats and other wildlife but they are often ‘tidied up’ without thinking about their value. Leaving hollow trees standing provides ideal roosts for bats and other wildlife, and sometimes lopping branches is all that it takes to make them safe. Even hollow branches on healthy trees can be important for bats. Remember bat roosts are protected from being damaged or destroyed even accidentally. If bats are roosting in the tree or branch you need to fell, you will need a licence before cutting it down (see Bats and the law ).
You can make your house accessible to bats by providing holes in the right places; however, it’s just a matter of chance if bats find them. Access holes should be no larger than 20 millimetres wide and the best places to put them are along eaves near the corners of buildings or at gable apexes.
These are like bird boxes but with a slit at the bottom for the bats to get in rather than a hole in the side. It’s best if they’re put up on trees in an area such as a conifer plantation where there are lots of insects but no natural roosts for bats. Bats will sometimes use boxes on houses, but don’t be disappointed if the box appears to stay empty. They should be put as high up as possible facing south. You may have a local bat group who could advise you, and the Bat Conservation Trust or Scottish Natural Heritage are always happy to provide advice.
Bats in the garden
Planting a wildlife garden can help to provide the insects that bats need, especially if there’s a pond and night-scented flowers and shrubs.
Help needed out of office hours?
If you have a problem with bats and you can’t get through to one of our Area offices, you can telephone the Scottish Natural Heritage Bat Helpline on:
Alternatively, you can try the Bat Conservation Trust National Bat Helpline on:
0845 1300 228
Bats in domestic properties
Sometimes bats can cause problems in houses and other buildings, see Problems with bats in your property? Scottish Natural Heritage employs trained and experienced bat workers who are there to provide practical advice on how to deal with these problems at no charge to householder. In recognition of the special set of circumstances associated with domestic situations, Scottish Natural Heritage policy is that roost visits will only be undertaken by our bat workers in cases involving enquiries from householders, whether they own or rent the property.
If you are experiencing difficulties with, or have concerns about bats in your property please contact your local SNH office or email [email protected] for advice. If the issues cannot be resolved by telephone or other correspondence, we will ask one of our bat workers to visit you, investigate the bat-related issues and discuss the possible solutions with you face to face. If you plan to do anything that may affect bats in your property, this may require a licence and you should contact SNH for advice about this.
Bats in non-domestic properties
In commercial premises, public buildings, hotels, schools, hospitals and other buildings not classed as dwellings, we will still provide verbal and/or written advice, but we will not normally send out a bat worker to undertake a roost visit. In these cases a specialist bat consultant should be employed to advise further as necessary. Some of these are listed in the IEEM Register of Consultants .
Advice for planners and developers
Are bats likely to be present?
There is no simple answer to this, but the guidelines Are bats like to be present? may help to identify those buildings or structures in Scotland that are either particularly attractive or unattractive to bats. Of course, as with any generalisation, there are are exceptions, so these broad criteria should be regarded as indicative.
More information on the roosting requirements of bats (and the various factors that influence the probability of bats being present at a site) can be found in the Natural England Bat Mitigation Guidelines .
Detail on recommended survey methodologies, equipment and timing etc can be found in the BCT bat survey guidelines (2nd edition). The aims of a survey are to:
- determine if, and to what extent bats are using a proposed development site
- identify the species present
- locate any roosts, foraging areas and commuting routes, as appropriate
The survey data are then used to assess how the proposed development may impact on the bats – see the IEEM Guidelines for Ecological Impact Assessment and the Bat Mitigation Guidelines .
For small-scale developments, i.e those affecting individual houses or small groups of associated buildings, a minimum of three activity (emergency/re-entry) surveys and a thorough inspection of building(s) both inside and out is required. The activity surveys should be undertaken at dusk and dawn and comprise at least one dawn visit. They should be spread over several weeks during the bats’ main period of activity, ideally with visits in June, July and August. The objective of these surveys is to: identify the species of bat present; locate their access point(s); provide an estimate of numbers; and determine the status of the roost (e.g. maternity, transition, male roost etc).
If a survey has been conducted during the winter and has reported suitable habitat for/evidence of bats a summer survey will be necessary before planning approval can be granted. Note that a bat survey cannot be included as a condition of Planning Approval but must be completed prior to granting planning permission. This is a requirement of the EPS legislation.
The level of survey required for larger developments, including infrastructure projects, needs to be considered on a case by case basis, with reference to the BCT guidelines.
Bat surveys and wind turbines
The current position of Scottish Natural Heritage regarding the existing guidance on bat surveys at proposed wind turbine developments is set out in the document Bats and Wind Turbines . This has been produced jointly by the Countryside Council for Wales, Natural England and Scottish Natural Heritage and acknowledges the need for further systematic data from UK wind farms on bat mortality at these sites and refers to current studies that are underway to improve our understanding.
Bats have very specific requirements and their choice of roosts is governed by factors such as temperature, proximity to suitable feeding habitat and, for a building, its age and construction. As a consequence, the creation of a new replacement roost that will be equally attractive to the bats as their original home can be difficult to achieve and the outcome often uncertain. Mitigation encompasses a range of measures to minimise and offset the impacts of a development on the affected bat population. These are to:
- minimise fragmentation/isolation of bat colonies
- minimise direct impacts on bat roosts
- minimise direct loss of foraging habitat
- incorporate measures to mitigate against the loss of continuity in key commuting corridors e.g. green bridges
- create new habitats or roost sites of real value to bats
If a bat roost will be unavoidably lost to development, knowledge of how the bats use the surrounding habitat, notably the identification of key flyways, will help in determining where a replacement roost should be located. The mitigation scheme should be informed by detailed survey undertaken in advance of an application for planning permission. The more information that can be collected on how the bats use their existing roost and the nearby habitat, the more likely the mitigation measures are to be successful.
Any proposed mitigation plan must be tailored to the circumstances involved. For the proposal to be acceptable, it must have a reasonable chance of success. There is a need to encourage novel techniques and support experimental studies to test the value of these. The two links (right) to the BCT Bat Mitigation Conference in 2007, provide examples of attempted mitigation in a range of circumstances, covering a range of species (including some that do not occur in Scotland), but note that the outcome is not always known.
Timing of works
Where proposed works will unavoidably affect bats or their roosts, they should be programmed to take place when the bats are not present. In general, works affecting a maternity roost, should normally only take place between the months of October to March inclusive. However, where major roof repairs are required, work may only be practical during the spring or late summer/early autumn to avoid the worst weather. In such cases, the months of April and September can be included in the timing of works. However, bats may be present for part of this time so special provisions may apply which would need to be specified on the licence. No work should take place between mid May and mid August in a maternity roost. Conversely, a hibernation site should not be disturbed during the period November to March inclusive and work may only take place in the remaining months of the year. Work in mating/swarming roosts should not take place during August to October inclusive. Note that weather conditions in the spring and autumn affect the above general timings – a cold wet spring will delay when female bats return to a maternity roost and this will have an influence on the date when work in the roost must cease. Similarly if the autumn is particularly cold, bats will enter hibernation earlier.
Artificial bat roosts
Currently, the most effective form of mitigation for the loss of maternity roosts of pipistrelle species is the heated bat house. This was originally based on an American (unheated) design available from Bat Conservation International. The heated version was developed in Britain for our cooler, less predictable climate and various models are now commercially available. A wide range of other (unheated) bat boxes are also commercially available including traditional wooden boxes to the much more durable modern woodcrete boxes.