Bat Surveys of Trees

We conduct bat surveys of trees throughout Wales, northern England and Scotland.

Most British bats have evolved to roost in trees. Features such as rot holes, cracks, flaking bark and old wood pecker holes can all be suitable for roosting bats. Many mature broadleaf trees are also important for a host of other wildlife and for their landscape and cultural values.

Unfortunately, our mature trees and the wildlife they support have for many years been under threat from misunderstanding and poor management. Many trees, thought to be dying or dangerous, continue to be unnecessarily felled or damaged by inappropriate tree surgery. It is not known how many bat roosts are been lost each year as a result of this type management.

UK legislation requires landowners and developers to carry out a bat survey for roosts prior to tree surgery taking place.

This page describes a three stage methodology for surveying and assessing trees’ potential for roosting bats.

Methodology

This methodology is agreed as best practice by Natural England, NatureScot, Natural Resources Wales and The Bat Conservation Trust.

Stage One – Ground Survey

Trees are surveyed from the ground with the aid of binoculars looking for features capable of supporting bat roosts, including rot holes, cracks, splits, woodpecker holes, folds, overhangs, wound callus rolls and flaking bark, and will be identified as one of the following categories:

• No Potential. Tree has no features capable of supporting bat roosts.
• Unknown Potential. Tree cannot be fully assessed from ground due to size or view obscured by leaves or ivy but is of a size, age and form to warrant further inspection.
• High potential. Tree has features thought to be capable of supporting bat roosts.The trees identified as high or unknown potential are tagged, recorded in a schedule and marked on a site plan.

A ground survey can take place at any time of the year.

Stage Two – Aerial Inspection

All trees identified as having unknown or high potential in the Stage One ground assessment are inspected from rope and harness or Mobile Elevated Work Platform with the aid of an endoscope and are allocated to one of the following categories:

• No bat roost found (3) – no potential. No features present, no potential for bat roosts.
• No bat roost Found (2b) – medium potential.Features present with potential for roosting bats but no evidence of bats found.
• No bat roost found (2a) – high potential. Features present with potential for roosting bats but no evidence of bats found. This includes features such as rot holes, cracks, splits, woodpecker holes, folds, overhangs, wound callus rolls and flaking bark.
• Confirmed bat roost (1) – Evidence of roosting bats recorded including scratch marks, staining, droppings and live bats.

The aerial inspections are carried out by licensed bat workers who are experienced in using endoscopes and qualified to climb trees.

The numbers of bats, species and location of exit holes are recorded using maps and digital photography.

An aerial inspection can take place at any time of the year.

Stage Three – Dawn and Dusk Emergence and Re-entry Surveys

During spring and summer an emergence count, with the aid of Anabat SD 1 and SD2 bat detectors, is recommended for roosts where bats are present to ascertain the number of bats using the roost and confirm the species. Numbers of bats, species, emergence times and location of exit holes are recorded using maps, digital photography and infra-red cameras.

A stage three survey is also highly recommended for trees with large cavities that can not be fully surveyed with an endoscope due to its size.

Licences to disturb European Protected Species 

Where possible, it is recommended that proposed developments avoid all trees with confirmed roosts and also those identified as having high potential for roosting bats.

However, if this is not possible a European Protected Species (EPS) license to disturb/destroy the confirmed bat roost(s) will be required from NatureScot, Natural Resources Wales or Natural England before any work on the trees can commence.

A Bat Mitigation Plan is required as part of the application process.

Stuart Spray Wildlife Consultancy can prepare Mitigation Plans and guide you through the licence application process.