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You can contact Stuart Spray Wildlife Consultant at the following addresses:

England: SSWC, 9 Basford Road, Manchester M16 0FT

Scotland: SSWC. Laundry Cottage, Clarencefield, Dumfries, DG1 4NA

Phone: 07894 081164

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Bat Surveys of Bridges and Viaducts

We specialise in bat surveys of bridges and viaducts throughout the UK.

Bats are known to roost in many different locations within old and new bridges and viaducts. Roosting locations in which bats have been recorded include:

  • Widening joints;
  • Expansion joints;
  • Gaps at the corner of buttresses;
  • Widening gaps (where the width of the bridge has increased, forming a gap between the original and new structure);
  • Cracks/crevices (usually over 100 mm deep) between stonework and brickwork where mortar has fallen out (locations include the underside of the bridge span and spandrel, parapet and abutment walls);
  • Drainage pipes and ducts; and
  • Internal voids within box girder bridges.

Species regularly recorded roosting in bridges include Daubenton’s, Natterer’s bats, pipistrelle Sp., brown long-eared and whiskered/Brandt’s bats.

UK legislation requires landowners to carry out a bat surveys prior to modification or repair of bridges and viaducts suitable for roosting bats.

However, roosts and potential roosts are often missed during inspections from the ground and/or activity surveys of very tall structures. This often leads to costly delays and may result in prosecution for damaging or disturbing a bat roost.

Stuart Spray Wildlife Consultancy has joined forces with Bell Access and Engineering Ltd (BAE) to provide close-up visual inspections of bridges and viaducts, no matter what the height or design, from rope and harness. As our licensed bat worker and rope technicians are all qualified to Industrial Rope Access Trade Association (IRATA) standards, we are able to inspect, using endoscope and strong lights, parts of the bridge or viaduct that can not be seen from more traditional ground surveys. With careful planning we aim ensure that maintenance works are completed on time and to budget without causing damage or disturbance to protected bat roosts.

This page describes a three stage methodology for surveying and assessing potential for roosting bats. A forth stage for license applications is also required if evidence of roosting bat is recorded.


This methodology is agreed as best practice by Scottish Natural Heritage, Natural Resources Wales, Natural England and the Bat Conservation Trust.

Stage One: Visual Inspection From The Ground – Also known as a Preliminary Bat Roost Assessment (PRA) 

The bridge or viaduct is surveyed from the ground with the aid of binoculars, strong light and endoscopes, looking for features capable of supporting bat roosts and evidence of roosting bats including live bats, remains of dead bats, droppings, feeding remains and possible roosting sites.

The structures are also assessed for their potential to be used by roosting bats and allocated to one of the following categories:

  • No Potential: Bridge/Viaduct has no features capable of supporting bat roosts.
  • Unknown Potential: Bridge/Viaduct cannot be fully assessed from ground due to size.
  • High potential: Bridge/Viaduct as features thought to be capable of supporting bat roosts .

Stage Two: Visual Inspection From Rope and Harness or Elevated Platform

Bridges or viaducts assessed as having features with high or unknown potential for roosting bats in the Stage One inspection that could not be reached from the ground are inspected during daylight hours from rope and harness using strong light and endoscopes.

All inspections are carried out by licensed bat workers who are experienced in using endoscopes and certified to work at heights.

Structures are allocated to one of the following categories:

  • Confirmed: Confirmed signs of bat presence/occupation and actual bat presence;
  • High Potential: Features present with high potential to support roosting bats. These include structures with points of access to the interior through degraded/ missing mortar/ brickwork, proximity to good foraging habitat such as woodland and/ or water and suitable crevices, dense ivy cover;
  • Moderate Potential: Features present that are able to support small numbers of roosting bats such as males in the summer or the winter;
  • Low Potential: Limited roosting potential. Structures in good condition with no access into structure visible. Few features of bat interest; and
  • Negligible:Roosting bats very unlikely to be present. Includes structures constructed from unsuitable materials e.g. prefabricated with no entrance opportunities.

Stage Three: Activity Surveys

Activity surveys are recommended for all bridge and viaducts with evidence of roosting bat or with features that are too complicated to be fully inspected with an endoscope.

Two dusk and one dawn activity surveys, with the aid of frequency division bat detectors, are conducted between May and September inclusive. Each emergence survey should start half an hour before dusk and finish 1.5 hours after dusk. The number of bat workers required to carry out the survey will depend on the number of features requiring further surveys.

Numbers, species, emergence/entry times and entry/exit hole locations are recorded using maps, digital photography and infra-red cameras.

The dawn surveys start two hours before dawn and at sunrise. As with the emergence count, the number of bat workers required to carry out the survey will depend on the size of the bridge and the number of features being surveyed.

Static remote bat recording units left over a period of several nights can also be extremely useful in establishing the status of a structure in terms of roosting bat.

Stage Four – Licenses to disturb a European Protected Species

Where possible, it is recommended that features with confirmed roosts or those identified as having high potential for roosting bats are avoided.

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

A Bat Protection Plan (BPP) is required as part of the application process.

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