Could there be bats in my tree, and what does that mean?

Bat legislation is one of the areas householders most often breach unknowingly, because it protects the roost feature itself, not just an occupied roost. A tree cavity that bats use in spring is protected in November when they are elsewhere. The practical consequence is that assessment comes before the work on any mature tree with the right features, and the assessment is far cheaper than the alternative.

Safety

What you'll need

• Binoculars
• A torch (optional)
• A camera

Step by step

1. Know which trees are likely candidates.Mature and veteran trees, especially oak, ash, beech and willow, and any tree with age-related features. Young smooth-barked trees are very unlikely to hold roosts.
2. Look for the roost features from the ground.Woodpecker holes, knot holes, splits and cracks in limbs, cavities where branches have failed, hollow trunk sections, loose or flaking bark, dense ivy cover, and old rot holes. These are what an ecologist calls potential roost features.
3. Look for the signs bats leave.Droppings on or below a feature — dry, crumbly and full of glittering insect fragments, which distinguishes them from mouse droppings — staining or polished wear around a hole entrance, and squeaking on warm evenings. Absence of signs is not proof of absence.
4. Watch at dusk in the summer months.The simplest check available to a householder is to stand back and watch the tree from about twenty minutes before sunset on a warm still evening between May and August, looking for bats emerging. Seeing bats emerge is conclusive; not seeing them is not.
5. Understand what is protected.Deliberately killing, injuring or capturing a bat, damaging or destroying a breeding site or resting place, and disturbing bats are all offences. The roost is protected whether or not it is occupied at the time, because bats are faithful to their sites.
6. Get a licensed ecologist involved before major work.For felling or significant pruning of a mature tree with roost features, a preliminary roost assessment by a licensed bat ecologist is the correct step. It is not usually expensive relative to the tree work itself, and it protects you.
7. Expect the outcome to be manageable.Where bats are present, work is normally still possible, but at a different time of year, under a method statement, and sometimes under a licence with the ecologist present. Outright refusal is rare. It is delay and process, not prohibition.
8. Stop immediately if you find bats during work.If bats are discovered while cutting, all work must stop at once and advice must be taken from a licensed ecologist or the statutory nature conservation body. Continuing after discovery is the point at which an accidental situation becomes a deliberate offence.
9. Tell your tree contractor to check.Competent arborists assess for roost features as a matter of course and will stop and take advice if they find them. A contractor who has never mentioned bats is one to question.
10. Retain features where you can.If a tree must be reduced rather than felled, retaining a hollow limb or leaving a standing monolith preserves the roost and the habitat. Ecologists and good arborists will often suggest this.
11. Consider it a positive.Bats eat vast numbers of insects, all UK species are harmless to people, and a garden with a bat roost is a garden doing something right. Bat boxes on mature trees are worth putting up, ideally in groups at different aspects.

Tips

• The National Bat Helpline gives free advice to householders and is the right first call for anything uncertain, including a grounded bat.
• Ivy on a mature trunk is itself a recognised roosting feature, which is another reason to check before stripping ivy off a big tree.
• The same protection applies to roosts in buildings — lofts, soffits, cavity walls and roof tiles — so the check matters before roof work as well as tree work.

Common mistakes

• Assuming no bats today means no roost — The protection attaches to the roost feature, not to occupancy. Bats return to the same sites year after year and are absent for months at a time.
• Felling a veteran tree without an assessment — It is the highest-risk situation for a bat offence, and veteran trees are the most likely to hold roosts. An assessment first is proportionate and inexpensive.
• Continuing work after finding bats — It converts an accident into a deliberate offence, and the penalties for deliberate offences are much more serious.
• Handling a bat with bare hands — A small number of UK bats carry a rabies-related virus. Bites and scratches are a genuine health issue, and the bat should be handled only with gloves and on advice.

Questions people ask