Lounge lights off, I’ve enjoyed watching a pair of bats in the summer evenings sky dancing over my back garden. Over the next couple of months they’re busy finding a mate and feeding on insects to build up their fat reserves for winter hibernation - a bat typically eats about a third of its own body weight in food per night. 

Bats are nocturnal animals that have adapted to a life in darkness, partly to avoid predation during daylight hours from birds of prey, such as Sparrowhawks. During the day, bats shelter in dark places (roosts), such as in hollow trees, roof spaces, under tiles and soffits, loose bark on trees, or in splits in the trunks and branches of trees. Artificial lighting placed near to or affecting bat roosts, access points and foraging routes can cause many problems, for example, by: 

  • Delaying or preventing emergence from roosts = reduced foraging time and missing the peak time of insect abundance (just after dusk), which can have a serious impact on their survival and the growth rates of their young. In some instances leading to bats abandoning or becoming entombed in their roost when the entrance is lit up as bats will be less likely to exit in these conditions; and
  • Affecting the feeding behaviour of bats away from the roost. Slower flying species, lesser horseshoes and greater horseshoes, for example, avoid illuminated areas and have to use poorer quality foraging sites. Badly located and designed lighting can act as ‘barrier’ blocking commuting and foraging routes. They can also lose out on food as insects are attracted to the surrounding lit areas, a so called ‘vacuum effect’. Linear features in the landscape, such as hedges, woodland edges, rivers and streams, are important for bats, both as feeding areas and navigation pathways that are used as they travel between roosting sites and feeding areas. Some bats, such as Daubenton's bat, specialise in swooping low over ponds and other water bodies where they feed on insects such as adult caddis flies, mayflies and other insects with aquatic larvae.

We have nine of the seventeen UK Bat Species here in Cumbria. Two of these, common to Cumbria but rare internationally, are particularly sensitive to lighting – the Brown Long-Eared and Natterers Bats. South Cumbria is a stronghold for them both with the large number of barns/old buildings and lots of woodland where these bats are able to roost and feed. 

Bats represent one fifth of the mammal world population. These nocturnal species play a crucial role in insect regulation, seed dispersal and pollination, and serve as good bio-indicators through their sensitivity to climate change and habitat loss. Dependant on insects for food in the UK, we know also that insect numbers are also significantly affected by artificial lighting. 

Are we properly assessing the impact of new lighting from developments and private security lights across South Cumbria and elsewhere on these critical bat roosting, commuting & foraging routes and feeding habitats? As decision makers we need think more about the night-time environment and do some site visits ‘out-of-office’ hours! 

We should remember, due to severe declines, all our bat species are legally protected. It is illegal to kill, injure, capture, or cause disturbance that affects populations of bats, obstruct access to bat roosts, or damage or destroy bat roosts. Very helpful guidance on artificial lighting and bats is available:  https://cdn.bats.org.uk/pdf/Resources/ilp-guidance-note-8-bats-and-artificial-lighting-compressed.pdf?mtime=20181113114229&focal=none