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It’s against the law to harm bats or their habitats. Do you know how – and when – to spot the potential for bats on site?

07/03/2016

Eight Associates Ecologists can help if you require a bat detector survey or advice about a protected species. Read our case study or give us a call to talk through your requirements.

In the UK, all bat species are protected by the Wildlife & Countryside Act (1981) as amended, Countryside and Rights of Way Act (2000) and the Conservation of Habitats and Species Regulations (2010). It is illegal to deliberately or recklessly kill, injure, capture or disturb bats, obstruct access to bat roosts or damage or destroy bat roosts, whether occupied or not. Changes made in 2007 makes incidental damage to the breeding site or resting place of any European bat species an offence too. Even relatively small tasks, such as repairing a roof, converting a loft, or changing bats’ foraging habitat can harm bats. Breaking the law could mean up to 6 months in prison, a fine of £5000 and serious reputational damage.

About half of all bat species use holes in trees for roosting. The other half use either caves or cavities, including those in buildings.  Even a crack in a building as small as 2cm across can be used by a crevice dwelling bat. If your project requires planning consent, the first step is for a bat specialist to conduct a bat survey to assess the potential for or evidence of bats on site. Depending on the potential for bats on site, it may then be necessary to conduct detector surveys to ascertain if the site is constrained by bats or not. If your project requires a site to be cleared, and there is a possibility that bats use a structure, then it should be surveyed by a bat specialist prior to demolition and early enough to ensure that there is time to conduct any additional detector surveys or mitigation procedures that may be necessary if the site is constrained by bats, before work begins on site.

There are four main types of bats; crevice-dwelling bats, roof-void dwelling bats, bats that need flight space in certain types of roost and bats that need flight space and flying access into the roost. Some bats are relatively common throughout England, while others are rare.

The survey identifies the type and number of bats, and how they are using the building or area. However, surveys can only be conducted at certain times of the year, when bats are active, and missing the survey window can lead to insufficient evidence and significant delays in the planning process. The optimal timeframe within which to conduct detector surveys is from May to August (inclusive).

Bats do not make nests or cause structural damage, so what should you look for? Bats look for shelter that is dark, a stable temperature, free from parasites, safe from predators or disturbance and sheltered from the weather. Temperature is important to female bats raising young in summer and maternity roosts tend to have a southerly or westerly aspect.  In the winter, hibernation roosts are often a cool space with high humidity.

As such, there are a range of possible roosting opportunities, in both modern and traditional buildings, which are similar to crevice and tree-cavity spaces found in the natural environment. For example, these could include behind fascia, beneath roof tiles, chimneys, attics and cellars. Moreover, bats can crawl into openings of just 15mm x 20mm.

The most obvious sign of bats is droppings, but even these can be hard to find. Bat droppings are mainly insect remains and, unlike rodent droppings, crumble easily to a powder of semi-shiny fragments. Other signs to look for are grease marks on the rafters, urine marks, cobweb free corners, or insect remains from a feeding perch.

The outside environment is important too. Bats use linear features such as hedgerows and tree lines as commuting pathways and for acoustic orientation.  Trees need to be assessed for their bat potential too. Hollow trunks, cracks, crevices, ivy cover, fractured limbs, deadwood in the canopy or stem all increase the potential. Ash, Beech, Oak and Scots Pine are often favoured by bats.

Trees classified as having high bat potential must be assessed for the presence of bats or roosts. Even if no evidence is found then the tree should still be treated as having a high bat potential during any arboricultural operations.

The presence of bats or roosts within a tree could be indicated by historical site records, sightings, bat calls, droppings, grease stains around openings or urine marks below openings.

If bats are confirmed, and arboricultural work is not urgently required as a matter of public safety, and the intended arboricultural operations have the potential to cause a direct disturbance to bats or destroy them or their roosts, work can only proceed under licence.  If bats aren’t confirmed and there is low potential for roosting bats, work can proceed.  If there is a moderate potential for bats, further inspection could be required and work should be carried out in a sensitive manner, in autumn or between March and April. If a tree has high bat potential, further inspection is required by a trained and experienced professional.

Timing is critical when dealing with bats. The potential for bats needs to be identified and investigated as early as possible within the survey window. Not doing so, can lead to lengthy delays. Proceeding without undertaking a survey can end in prison. When the survey results are known, the bat specialist will help plan the next steps.  Building work which could disturb bats should only be carried out when bats are absent and, depending on type of roost, is best conducted in spring or autumn.  The bat specialist will be able to advise how to avoid harming them. Bat licences can be applied for from Natural England if the project can’t avoid disturbing bats or their habitats and a mitigation strategy devised to enable the project to go ahead without breaking the law.

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