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Bats and Buildings

What do bats look for in a home?

Like us, bats are looking for shelter that is clean (free of disease and parasites), comfortable (protected from the weather) and secure (safe from predators and disturbance). However, bats also have unique requirements and may live in several different roosts throughout the year depending on their seasonal needs. 

Brown long-eared bats in a roof corner

 

Temperature

Temperature is very important to bats. Bats are different to us in that they look for warm roosts in the summer and cool roosts in the winter.

Summer: Bats usually only have one young a year. Mother bats gather together and find somewhere warm to rear their young called a maternity roost. Males will form smaller roosts elsewhere that are often cooler than the needs of the females. Generally maternity roosts are usually between 30 and 40°C, however species can have their own unique preferences and studies have shown that even a 1.5°C difference may influence bats to choose one building over another. It is always best to provide a number of different options for bats, so that they can choose the right roost with a temperature based on their needs.

Winter: British bats feed on insects which are scarce in the winter. Bats have adapted to this seasonal scarcity by going into hibernation where they lower their body temperature to the ambient temperature or just above. Hibernation roosts are often a cool space with high humidity. For most species this is generally between 0 and 6°C, however horseshoe bats prefer slightly warnmer conditions of 6 - 10°C.

Aspect and orientation 

Summer maternity roosts in the northern hemisphere often have a southerly or westerly aspect for maximum solar heating. Male roosts and hibernation sites typically have a northerly aspect.

Which bats roost in buildings?

All UK bat species have been known to use buildings, but some species are more building reliant than others. Different bat species select different types of roosts in buildings since they look for sites comparable to those chosen in natural habitats.

Bats that use buildings can generally be divided into four categories, although there is regional variation and some species can occupy more than one category:

  • Crevice-dwelling bats (which tend to be hidden from view) include the common pipistrelle, soprano pipistrelle, Nathusius’ pipistrelle, Brandt's bat and whiskered bat.

  • Roof-void dwelling bats (that may be visible on roof timbers) are serotine, Leisler's bat, Daubenton's bat and barbastelle.

  • Bats that need flight space in certain types of roost are Natterer's bat, and brown and grey long-eared bat.

  • Bats that need flight space and flying access into the roost are greater horseshoe and lesser horseshoe bat.

Creating roosts in buildings

The advice below describes general principles to consider when providing new roost spaces for bats. It does not provide sufficient information for mitigation when a roost is already present. Work on existing roosts should be covered by a Natural England EPS licence.

Access, size of roost space and structure

Crevice-dwelling bats can crawl into their roosts via gaps from as small as the width of our thumb. The roost area should contain a crevice of this approximate size gap that the bats can roost in. The height of entry can be from 2 - 7m.

Roof-void dwelling bats require similar dimensions to access the roost but typically need timber joists or beams on which to roost. The height of entry can be from 2 - 7m.

Bats needing a flying area require the same access dimension as mentioned above. These areas are typically empty / uncluttered loft spaces to allow flight.

Horseshoe bats need a larger access so that they can fly (instead of crawl) directly into the roost. As above, the roosting area should not be trussed / cluttered, to allow flight.

Lesser horseshoe bats

 

Materials and structure

Materials for the roosts should be rough (for grip), non-toxic or corrosive, with no risk of entanglement. The materials should also have suitable thermal properties that reduce 24 hour fluctuations but allow maximum thermal gain for summer roosts.

 

Find out more



Bats and Buildings (2 MB) - 19/04/12
Guidance for built environment professionals,consultants, building owners and managers on conservation actions to promote and cater for bats in buildings.


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