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Mammals and ancient trees

Which UK mammals love to live in ancient trees?

Many UK mammals, such as squirrels, badgers, otters, dormice and mustelids (which are species like polecats, pine martins, weasels and stoats), live for at least some of their time in woodland and most make use of trees in some way.

Bats particularly like woodland too, although they live in other places as well, because of the abundance of insects available to eat and the variety of niches trees offer for bat roosts (defined as any site a bat uses for shelter and protection). Of the 17 species of bat found in the UK, all frequent woods, with a few being woodland specialists.

Provided it has plenty of places for them to roost, any woodland can be home to bats. However, woods that are large, semi-natural, broadleaved, mixed or under-managed, and contain lots of trees with splits, cracks flaking bark and crevices, are more likely to attract bats.

Bats do like veteran and ancient trees. Older trees have more roosts than younger ones for the following reasons:

  • Potential for roost sites increases with a trees age, size and presence of damage
  • Once a tree is used by bats, there is a greater chance it will be used again

Older, ancient, and/or damaged trees usually have lots of nooks and crannies. Rot holes, snags and cracks, gaps made by splits and loose bark, dead and dying wood, behind ivy and other dense climbers, and even holes make by woodpeckers, can all make potentially good roost sites.

Any tree species can be suitable - but oak and beech often seem to be the preferred option. However, bats rarely restrict themselves to one tree. They change their roost sites frequently, sometimes every two to three days, looking for small differences in temperature and humidity. For instance, in hot weather bats can suffer dehydration, but by tucking themselves up inside a damp rot hole, they can avoid this.

The law and bats

All bats and their roosts are protected by law. It is an offence to destroy, damage or disturb a bat roost (even if the bats are not present at the time).

That means that ancient trees which have bat roots in them are also protected.

Woodland managers must identify and conserve bat roosts in their wood. It is also compulsory to seek advice from the relevant statutory agency before doing any maintenance work on a tree with a bat roost.

Bats are adapted to the loss of tree roosts through natural causes, such as trees falling apart over time or being blown down by the wind. They will simply move to another nearby tree. However, the loss of several roosts in one go, such as might happen through clear-felling, would have a devastating impact on bat populations.

If you spot a bat roost while walking in a wood, please let your local bat group know.

Visit the Bat Conservation Trust’s website to find details of your nearest group

For further information:

Veteran Trees: A guide to good management

Visit the Bat Conservation Trust (BCT) website at www.bats.org.uk

In addition, check out the BCT’s following publications:

Woodland Management for Bats - a good practice guide on how bats use woodlands and how they can be protected

Bats and Trees in England - a leaflet that explains the laws and guidelines protecting bats in trees

Squirrel eating nut