Listed Buildings Article on Bats

Overview 

The UK supports 18 bat species, 17 of which are known to breed across the UK. This represents nearly a quarter of the country’s mammal species. 

Bats are the only mammals capable of sustained flight using a thin membrane of skin supported by what would be their fingers, with the thumb used for climbing. Their family name, Chiroptera, means ‘hand wing’. 

They navigate using echolocation, emitting high-frequency sounds to detect prey and obstacles. They are nocturnal, emerging at dusk to hunt insects such as midges, moths, and lacewings. Bats roost in a variety of locations, including trees, hedgerows, buildings, tunnels and caves, depending on the species and rely on woodlands, hedgerows, watercourses, and low-light areas for feeding and navigation. 

Habitat loss, building work, and reduction in insect prey have caused population declines over the past century and conservation efforts are being led by the Bat Conservation Trust and local bat groups, focusing on protecting roosts, restoring habitats, and monitoring populations. 

Common pipistrelle bat (image credit Jon Hayter) 

What it means for Listed and Heritage buildings 

Bats use many different building types and structural features as roosts, with the surrounding grounds, nearby trees and the landscape setting important for individual species requirements. With the loss of natural roost sites such as veteran trees, woodland and cave systems, bats have had to find alternative roosts in buildings, ideally with suitable foraging habitat nearby, such as parkland, grassland, gardens, and farmland. Bats also use buildings because they are more thermally stable and safer environments with less competition from birds and other mammals. 

As long-lived animals, bats require multiple suitable roosting structures for their life cycle requirements. In summer they need stable, warm, dry roosting environments to give birth and raise their young often referred to as maternity roost sites. In the winter they need stable, cold and humid roosts known as hibernation roosts. A variety of roosting places are important because although bats can regulate their body temperature, direct exposure to the weather or disturbance can disrupt this, leaving them vulnerable especially when food resources are scarce.

Depending on the number of microclimates and size of internal spaces, a building may accommodate just one or several different species and types of roost, roosting sites can be used occasionally or frequently such as day roosts or night roosts, and some buildings have records of continuous use by bats for decades in a variety of guises. The aspect, situation and construction of a building will create different temperatures and roosting and hibernation opportunities suitable for bats, hence why historic and older buildings and structures provide longevity and therefore a high suitability for multiple bat species.

Different features/ different bats 

Crevice-dwelling bats such as pipistrelle, serotine and myotis species, crawl into their roosts via gaps within the building’s construction, these roosts can be between roof coverings, within timber framework, cavity walls, between wall plates and in masonry.

Serotine bat within roof void (image credit Jon Hayter) 

Brown long eared bat between a wall and roof rafter union (image credit Jon Hayter) 

Roof-void dwelling bats such as long eared can use similar gaps, but others such as the horseshoe species also require unobstructed open flight access into the roost and these species are predominantly found within internal open loft spaces. The height and type of entry point varies between species but is usually between 2–7 metres from the ground.

Evidence of bats

Finding bats requires skills and expertise and should be undertaken by a licensed bat ecologist as disturbance can be heavily detrimental depending upon timings within their life cycle. Bats tend to choose dark, inaccessible places, and are small and usually quiet and inactive when roosting and a single bat squeezed motionless in a mortar gap is likely to remain unnoticed, likewise a small cluster of bats situated at the extremity of a loft in the pitch dark is also difficult to spot.

Nevertheless, signs of bats are possible to interpret and can include the following.

• Bat droppings; These are often found below the places where bats roost. They can be found on higher surfaces such as walls or windows as well as the floor. Bat droppings crumble to a fine powder when crushed, whereasrodent droppings usually harden with age. Fragments of insects will be visible in the bat droppings under torchlight. It is sometimes possible to identify the bat species from the appearance of the droppings, but good practice is to confirm species identification with DNA analysis.

• Insect remains; Some species of bat capture moths, butterflies, cockchafers or other large insects on the wing and return to a feeding perch to consume them. The wings or wing-covers are discarded and may accumulate below the perch.

• Smell; Well-used roosts may have a distinct musky smell. Occasionally this can be very strong, particularly in unusually large maternity and hibernation roosts where there is inadequate ventilation or dampness.

• Urine; Shiny surfaces, such as glass, polished wood, plastic or stone, may show urine spotting or staining.

• Grease marks and staining; Bat fur contains oils to keep it in good condition. A characteristic dark stain might be seen near a roost entrance or favoured roosting spot.

Pipistrelle droppings found on window ledge below day roost in window lintel and droppings and feeding remains of beetle exoskeletons and butterfly wings in a known horseshoe roost (images credit Jon Hayter) 

What it means for your project 

The absence of signs does not necessarily mean that no bats use the site, especially during the winter months when hibernating bats remain motionless for long periods of time in torpor or single animals are located between internal roof linings and external roof coverings. 

Building works need to be carefully programmed not to clash with bats’ occupancy of their roosts. You must get advice from a licensed bat ecologist about the timings of works, but usually the best time is during spring and autumn when the bats are not in hibernation or in maternity roosts, the most sensitive periods. You also need to plan ahead, in case you need a bat emergence, re-entry, or activity survey. These are undertaken when bats are active between May and September, these are used to inform any subsequent licensing. All species of bat, their breeding sites and resting places are strictly protected in England under the Wildlife and Countryside Act 1981 (as amended) and the Conservation of Habitats and Species Regulations (2017). It is illegal to kill or injure bats, disturb them or to obstruct or destroy their roosts (even if the bats are not inside at the time). 

Having bats in a building does not necessarily mean that you cannot carry out building or repair works, it would mean that a suitable bat mitigation license will be required to be in place prior to any works starting which affect the bat roosts. Once the licence has been approved and all other consents are in place, you will be able to begin the building work subject to any timing restrictions and mitigation conditions stated in the licence method statement and documentation. It is usual that a licensed ecologist will need to be present to oversee these works through to completion. 

Conclusions 

Bats are fascinating, ecologically important mammals in the UK, controlling insect populations and contributing to biodiversity. Protecting their habitats, respecting legal protections, and supporting conservation efforts are essential for their survival and recovery. 

As custodians of some of the most suitable structures for bats it is important that ecologists and all disciplines involved in the management, upkeep and repair of these structures communicate and collaborate to enable a positive outcome for both bats, listed and historic buildings, so both are continued to be protected into the future. 

HCUK group can help with all your ecology and heritage building requirements, we have licensed and experienced ecologists who can support you through all stages of your development. I personally have 8 years of experience undertaking bat surveys and obtaining protected species licenses for bats in order to support your project.