Potential roost features on trees in a survey
Assessing potential roost features answers one question: can this tree be felled without committing an offence. Here is the escalation from ground assessment to licence.
A potential roost feature is any part of a tree capable of being used by a roosting bat, and the assessment of potential roost features on trees exists to answer one question: can this tree be felled or pruned without committing an offence. Everything in the survey, from the binocular inspection to the third emergence visit, is aimed at that.
The features themselves are ordinary tree defects. Woodpecker holes, rot cavities, frost cracks and longitudinal splits, lifting or loose bark, knot holes, hollowing limbs, dense ivy, cankers and the flush cuts left by old branch removal. What makes them relevant is that a crevice a few millimetres wide, dry and sheltered, is a roost to several British species.
What counts as a feature and what does not
The Bat Conservation Trust good practice guidelines, now in their fourth edition, set the framework most consultants and most local planning authorities work to. A feature qualifies where it offers a cavity or crevice with suitable dimensions, an entrance a bat can use, and conditions inside that are stable enough for the species present in the area.
Depth matters as much as the opening. A shallow flaking of bark on a dead stem is not a feature. The same bark lifting over a 400 millimetre dry void with a clean flight line to it is.
Position matters too. A cavity two metres above ground on a stem surrounded by dense scrub is less likely to be used than one at six metres with an unobstructed approach, though neither can be ruled out on that basis alone.
Ivy deserves separate mention because it is the feature most often dismissed. Mature ivy on a trunk creates a stable thermal envelope that some species use routinely, and it cannot be inspected from the ground at all.
The ground level assessment and where it stops
A ground level tree assessment is carried out with close-focusing binoculars, a high-powered torch and a systematic circuit of the tree at different angles, recording each feature, its height, aspect, dimensions where visible and any field signs. Staining below a cavity, droppings on bark or at the base, scratch marks around an entrance and audible chittering on a warm evening are all field signs, and their absence proves very little.
This is where the assessment usually ends and where it usually should not. The limits are straightforward. You cannot see into a cavity from below. You cannot assess a feature on the far side of a dense crown. You cannot judge the internal volume of a split from twenty metres.
An assessment that records four features at height and then concludes negligible roost potential is doing something other than surveying. A reviewer should send it back.
Timing is a smaller constraint than people assume. A ground assessment can be done at any time of year, though the crown obstructs the view in full leaf, and winter inspection of a deciduous tree gives a better result. The arboricultural survey under BS 5837:2012 that accompanies most applications is a separate exercise with a separate competency, and reading it alongside the ecological record is worth doing carefully, as the note on reading a BS 5837 tree schedule column by column sets out.
Climbing inspection and endoscope work
Where features cannot be assessed from the ground, the next step is aerial inspection: a roped climbing survey, or a mobile elevating work platform where access allows.
The person doing it needs two competencies at once, arboricultural climbing and ecological survey, and in practice that is either an ecologist with a climbing qualification or a climbing arboriculturist working under an ecologist's direction. Most authorities will accept either where the reporting is clear about who did what.
Equipment is an endoscope with a flexible probe, a torch, and a means of recording. The inspection records the internal dimensions, whether the cavity is dry, the presence of droppings, feeding remains, staining or grease marks, and whether any bat is present. A bat in the cavity ends the assessment and starts the licensing conversation.
Two cautions. An endoscope cannot reach every part of an interconnected cavity system, so a negative inspection reduces the survey effort required rather than removing it. And the inspection itself can disturb a roosting bat, which is why it is carried out by someone competent to stop when they should.
Categorising the tree and what follows
The guidelines place each tree in a category of roost potential: negligible, low, moderate or high. The category sets the survey effort.
| Roost potential | Typical further survey |
|---|---|
| Negligible | None |
| Low | One dusk emergence survey |
| Moderate | Two surveys, usually one dusk and one dawn |
| High | Three surveys across the season |
Verify the current requirement against the published edition rather than a previous project, because the effort tables have been revised. Where a tree carries several features, the category reflects the best of them, and surveys have to cover all the features rather than the most convenient one. On a large tree that means more than one surveyor.
Seasonal limits on further survey
The ground assessment and the climbing inspection can happen at any time. Emergence and re-entry surveys cannot.
The recognised season runs from May to September, with May to August the optimal period, and results from the margins carry less weight. A survey in late September that records nothing will usually be read as inconclusive rather than negative.
The programme consequence is blunt. A moderate or high potential tree identified in October will not have a completed survey before the following May, and no amount of pressure on the ecologist changes that. Identify trees with roost features at the feasibility stage, alongside the tree survey that informs the layout, and the delay disappears into the design period instead of the determination period.
How the finding changes the felling method
Where a tree with features must be removed and surveys have not confirmed absence, the answer is not always a licence. A precautionary method statement, agreed with the authority and supervised by a suitably licensed ecologist, is often accepted for low potential trees.
Soft felling is the usual technique. Sections containing features are cut carefully, lowered rather than dropped, and left in a secure position overnight with the feature facing downward so that any bat present can leave of its own accord. Work is timed to avoid the hibernation period and the maternity season, which in practice leaves narrow windows in spring and autumn.
Supervision is not a formality. The ecologist stops the work if a bat is found, and from that moment the work cannot proceed without a licence.
When a licence becomes necessary
All bat species are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017. It is an offence to damage or destroy a breeding site or resting place, and the offence does not depend on a bat being present at the time. A roost is protected whether occupied or not.
Where a confirmed roost will be lost or damaged, a European protected species mitigation licence from Natural England is required before the works. The application needs the survey data, a method statement, a mitigation and compensation scheme, and evidence that the three licensing tests are met. Planning permission has to be in place first.
A survey of this kind must be carried out by a suitably licensed ecologist. A Protected Species Survey drafted with AI assistance can carry the structure, the legal framing and the reporting headings, and the survey itself, the judgements and the sign-off belong to that professional. For specialist technical reports, qualified professional input may be required.
Where trees are retained rather than removed, the protection measures on site matter just as much, and the tree protection barrier specification under BS 5837 is the document that keeps them alive through construction.
Browse the 66 PlanScope report types to see how the ecology and arboricultural documents fit together in a submission.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Can a ground level assessment alone rule out bat roosts in a tree?
Only where no features are visible. Where features are recorded at height, on the far side of a dense crown or behind mature ivy, a ground inspection cannot assess them and a conclusion of negligible potential is not supportable. The next step is a climbing inspection or a mobile elevating work platform with an endoscope.
How many emergence surveys does a tree need?
The effort follows the roost potential category. One dusk survey for low potential, two for moderate and three for high is the usual pattern in the Bat Conservation Trust good practice guidelines. Check the current edition, because the tables have been revised, and note that all features on a tree must be covered, not just one.
When can emergence surveys be carried out?
Between May and September, with May to August treated as the optimal window. Surveys at the margins of the season carry less weight and a negative result in late September is usually read as inconclusive. Ground assessments and climbing inspections can be done at any time of year, so identify features early.
Is a roost protected when no bats are in it?
Yes. It is an offence to damage or destroy a breeding site or resting place of a bat whether or not a bat is present at the time. That is why an unoccupied cavity identified during a climbing inspection still constrains the felling method and, where the feature will be lost, can require a licence from Natural England.
What is soft felling and when is it acceptable?
Sections of stem containing features are cut carefully rather than dropped, lowered under control, and left secure overnight with the feature facing downward so any bat can leave. It is generally accepted for low potential features under a precautionary method statement supervised by a licensed ecologist, and work stops immediately if a bat is found.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.