The implementation and effectiveness of bat roost mitigation and compensation measures for Pipistrellus and Myotis spp. and brown long-eared bat (Plecotus auritus) included in building development projects completed between 2006 and 2014 in England and Wales.
We investigated the implementation and effectiveness of bat roost mitigation in building developments completed between 2006 and 2014 in England and Wales. Common and soprano pipistrelle Pipistrellus pipistrellus and P. pygmaeus, brown long-eared bat Plecotus auritus and any of the Myotis spp. were selected for the study. Building inspection and emergence/re-entry surveys were carried out at 71 sites during 2017 and 2018. Implementation: 61% of new roosts/access points were implemented precisely as specified, 19% deviated, 11% were absent and 1% were damaged. The remaining 8% were enhancements rather than mitigation or compensation. Effectiveness: 14% of sites did not retain roosting bats at all, 86% of sites had some bats post-development but only 13% maintained or increased numbers of all target species. Only 18% of new roosting provisions were occupied by bats post-development compared to 52% for adapted buildings and 25% for retained roosts. No bat lofts in new buildings were occupied in comparison to 55% of those in adapted buildings and 65% where bat loft roosts were retained after works. Breeding brown long-eared bats were least likely to return in similar numbers, particularly in roost destruction cases. Bat boxes mounted externally on buildings showed the highest occupation rate regardless of species. Common pipistrelle showed a preference for these over tree mounted boxes; the opposite was true for soprano pipistrelle. Only 8% of new, 8% of adapted and 21% of retained access points were used. These low percentages may be because most roosts were accessed from only one entrance point although multiple entrance points were provided at most sites. Significant relationships were observed between bat use and aperture width and height above ground level. The findings give important insights into degrees of implementation and effectiveness and how these might be improved, through changes in the licensing process, associated policy and guidance, to serve bat conservation. Further investigation is necessary to drive greater improvements (for example, for other bat species).