UK Ecological Survey Consultants - Ecology Durham - Ecology Northeast

Bat Assessment and Mitigation

At Woodland’s Hall, Knitsley, Durham

Woodlands Hall is a large stone built ‘traditional manor house’ with a slate roof and structural surveys have shown the Hall to be in need of extensive repair works. The new owner of the hall intends to conduct various works including stripping away tiles, replacement of underfelt, purlins and ridge beams as well as replacement of bay and sash windows throughout the building. Clearly, there is potential that this work may impact on roosting bats and Elmer Ecology was commissioned in April 2014 to conduct a bat scoping report on the Hall.

From a client’s perspective, there is always a fear that bats will be discovered making use of building and that this will create building constraints and incur significant costs, however this project demonstrates that bat mitigation costs are not significant when related to wider build costs, and that on most occasions it is possible to identify a method for mitigating any impacts on bats whilst enabling the development to progress.

During April, a scoping survey / bat risk assessment was conducted by Jonathan Elmer with another licenced surveyor and findings. The survey concluded that habitat surrounding the hall was particularly suited to bats and this was re-enforced by Durham Bat Group who provided fairly extensive records of bats within the adjacent 2km.

Inspection of the building exterior also identified various possible cracks and gaps through which bats might enter, and in particular these were seen adjacent old bay and sash windows, indeed evidence of urine staining was seen next to a window. An internal inspection also yielded evidence of bats and droppings were seen on external window sills as well as two small piles directly on the loft boarding beneath the slate roof. These were sent for DNA analysis and were found to be from Whiskered Bats Myotis Mystacinus. Clearly, the scoping survey had produced evidence of bats so a more in depth survey was warranted.

During June two dusk emergence surveys and one dawn re-entry survey was conducted with the goal of clearly establishing the location and type of the roosts, the species and numbers of bats using roosts. This information collectively enables establishment of the conservation significance of the Hall and the significance of impacts associated with proposed works. Surveys were conducted and showed the presence of various summer roosting sites for Common Pipistrelle Pipistrellus pipistrellus as well as a maternity roosts located behind the frame of an old bay window. This was discovered as the owner accidentally disturbed the roost by opening the window releasing a swarm of some 35 bats. Throughout these surveys, we were not able to directly record the emergence or re-entry of the Whiskered Bats identified through genetic analysis which demonstrates the fallibility of survey techniques and the need to use a variety of methods to assess such a property.

Given the potential that bats may be using the hall for both roosting and hibernation, Natural England advise that works should be conducted in April after bats have emerged from hibernation but before they have settled into maternity roosts, or September / October after the pups have fledged but before bats re-enter hibernation roosts. The window for works is tight, but correctly timing the works for a period when bats are least likely to be present represents the most effective mitigatory measure. In addition, various devices will be used to exclude the bats from roosts prior to the works commencing.

However, there is still a chance that bats will be disturbed during works and so a licenced bat worker will oversee all dismantling activities and any bats found during refurbishment of the roof and windows will be removed to the safety of a pre-erected artificial bat roost – free to return of their own accord when works have been completed.

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