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)  .

Bat roosts

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.