Bat Mitigation report

Reviewing the evidence on mitigation strategies for bats in buildings: informing best-practice for policy makers and practitioners.

A report has just been published by CIEEM that reviews the effectiveness of mitigation for bats within buildings. This study aimed to provide evidence to planners, developers and ecological practitioners on the efficacy of bat roost mitigation and compensation to help them ensure that mitigation approaches are evidence-based and beneficial for bats.

Why was this study needed?

“Despite the relatively widespread use of artificial bat roosts as both a mitigation strategy and habitat enhancement tool, relatively little research has been conducted on their effectiveness. Most research has focused on pre- and post-development case studies which, whilst valuable, are rarely generalizable. Given that the amount of data collected annually by ecological practitioners dwarfs that which could be collected by research scientists, in this project we aimed to harness this resource to assess the effectiveness of bat mitigation in buildings”.

You can read the report in full HERE.

In summary…

  • Modifying a roost has a less significant impact than destruction of a roost (with the provision of a compensatory roost), with re-roofing works being the most successful at retaining similar-sized roosts.
  • Provision of bat lofts has more success than provision of bat boxes (only 31% of sites that provided bat boxes as the primary mitigation were considered successful).
  • The probability of pipistrelles occupying a new bat loft was strongly dependent on the number of roost entrances provided.
  • Monitoring efforts varied widely between projects, including the provision of information from the monitoring visits. The more monitoring visits undertaken, and the longer the monitoring period, the more likely bats were to be found.

This is a very interesting and much needed review.


Acorn Ecology provide expert advice for protected species on development sites. We have experience of applying for a wide range of mitigation licences and have a good success rate. See our case studies for examples of past projects.


If you have bats on site and need advice, please get in touch with your nearest branch today or email

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Bristol: Tel: 0117 923 2768 / Mobile: 07971 994324

Guildford: Tel: 01483 382821 / Mobile: 07443 652988

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