Timing tree works around bats and nesting birds

Timing tree works around wildlife is a legal question with two different answers. For nesting birds, the law protects the active nest rather than a season, so working outside the breeding period is a way of avoiding the offence rather than a defence to it. For bats, timing does not help at all in the same way, because the roost is protected whether or not a bat is in it on the day the chainsaw starts. A winter fell that removes a tree with a hibernation roost is not a safe option, it is a different offence.

So the sequence is: assess the tree for bat roost features first, then choose a season, then check for nests immediately before work.

Why timing is a legal question

Two pieces of legislation do the work. Under the Wildlife and Countryside Act 1981 it is an offence to intentionally kill, injure or take a wild bird, or to intentionally take, damage or destroy the nest of a wild bird while it is in use or being built, or to take or destroy its eggs.

All UK bat species are protected under the Conservation of Habitats and Species Regulations 2017. The offences include deliberately capturing, injuring or killing a bat, deliberately disturbing one, and damaging or destroying a breeding site or resting place. That last limb is the one that catches tree work, because it applies to the roost itself and does not require a bat to be present.

Neither of those obligations depends on planning permission. Consent for works to a protected tree, or the absence of any need for consent, has no bearing on them at all.

The breeding bird season and what it restricts

The main breeding season runs from around March to August, with some species active from February and others still on second or third broods into September. Treat those dates as guidance about risk rather than as a permission structure. A blackbird nesting in a laurel in October is as protected as one nesting in May.

What follows in practice. Works planned between March and August need a nesting bird check by someone competent, carried out immediately before the work rather than a fortnight earlier, and recorded in writing with the date, time and findings. Where an active nest is found, the affected part of the tree is left until the young have fledged, and the remainder can often proceed with a buffer.

Ivy, dense evergreen cover and old ivy stems on trunks are the features that hold nests people miss. Hedges are worse than trees on this point, and a hedge trimmed in June is a much more common offence than a tree felled in June.

Bats, where timing does not help

Because a roost is protected when empty, the first question for bats is whether the tree has roost features at all. Timing comes second. That assessment comes first, and it determines everything afterwards.

A tree with no roost features can usually be worked at any time of year, subject to the bird check. A tree with moderate or high roost potential needs survey work by a licensed ecologist before any decision about timing, and possibly a licence from the statutory nature conservation body before works proceed.

A Protected Species Survey and any associated mitigation licence require a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017. That is a legal requirement rather than a recommendation, and a drafted report is a starting point for that professional rather than a substitute for their survey and their licence.

Assessing roost potential in a tree

The ground level assessment looks for potential roost features, and an experienced surveyor works round the tree with binoculars and a torch.

• Woodpecker holes and other cavities, including old pruning wounds that have become hollow
• Splits, frost cracks and lifted or loose bark, particularly on dead limbs
• Knot holes, snapped branch stubs and hollowing stem cavities
• Dense ivy cover, which both provides roosting space and conceals features
• Signs of use, such as staining below an opening, droppings on bark or feeding remains

Trees are then categorised by roost potential, following the recognised good practice guidelines for bat surveys, from negligible through low and moderate to high. The category drives the survey effort, and it also drives the working method: a tree with low potential may proceed with a careful sectional dismantle under supervision, while a high potential tree will not.

Record the assessment with photographs and a sketch showing each feature and its height and aspect. That record is what allows a later survey to be targeted, and it is also what demonstrates due diligence if anything goes wrong.

Aerial inspection and emergence surveys

Ground level assessment has obvious limits, and features on the upper side of a limb are invisible from below. Where potential is moderate or high, the next step is either an aerial inspection by a climbing ecologist with an endoscope, or dusk emergence and dawn re-entry surveys.

Emergence surveys cannot be done in winter, which is why a project that discovers a roost feature in January may face a wait of several months. That delay is the single most common reason a householder tree job overruns, and it is avoidable by assessing the tree at the design stage rather than the week before the contractor arrives.

Working outside the busiest seasons

The window most ecologists recommend for tree works where features are present, once survey has confirmed no roost, is early autumn. Bats are still active, so they can move if disturbed, and the bird season has finished.

Winter looks convenient and carries its own risk, because bats in torpor cannot move and a hibernation roost damaged in January is the worst case for the animals. Mid-spring carries the bird risk. Summer carries both the bird risk and the maternity roost risk, and maternity roosts are the ones where an offence is most serious.

Illustrative example: a mature ash with a woodpecker hole at 6m and lifted bark on a dead limb, which a householder wants removed in July because of a garden project. The honest answer is that July is the worst month available. A ground assessment in April, an aerial inspection in May, and works in late September costs a season and removes the legal risk entirely.

Pre-works checks and who can do them

A nesting bird check can be carried out by a suitably experienced arboriculturist or ecologist, and it must be immediately before the work. Put it in the contract, with a requirement to record it and to stop if a nest is found.

Bat work is different. Survey, licensing and any supervision of works where a roost is confirmed are for a licensed ecologist, and an arboriculturist without the relevant licence cannot take that role. Where a Preliminary Ecological Appraisal has already been prepared for a wider scheme, check whether the trees were covered, because appraisals commissioned for a building often exclude climbing inspection.

Where the works are also subject to a Tree Preservation Order or sit within a conservation area, the wildlife position runs in parallel with the consent process rather than replacing it, and the arboricultural case belongs in the tree survey. Felling in a woodland raises a further consent requirement, as set out in woodland felling licences.

If a nest or roost is found

Stop work on that part of the tree immediately. Do not attempt to move a nest, and do not block an opening that bats may be using.

Then record what was found, with photographs and the time. For a nest, leave the section until the young have fledged and take advice on how much of the surrounding canopy has to be left with it. For a suspected roost, contact a licensed ecologist before anything else happens, because what follows may require a licence and a specified working method.

A contractor who finds a roost and keeps going exposes both themselves and the landowner. Make it explicit in the instruction that stopping is the required response and that the cost of the delay sits with the project rather than with the contractor.

This is general guidance, not legal advice; check the position with a licensed ecologist and your local planning authority before carrying out works to any tree with roost potential.

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