Citation
Pringle, H., Siriwardena, G.M. & Toms, M.P. 2017. Informing best practice for mitigation and enhancement measures for Barn Owls. BTO Research Report 692: British Trust for Ornithology, Thetford
Overview
By using the BTO's ring-recovery database, this report analyses the dispersal movements of UK Barn Owls to inform placement of mitigation measures along the route of the HS2 rail-link.
In more detail
- The introduction of the High Speed Two (HS2) rail line represents a national-level impact on Barn Owls and appropriate measures have been identified as required to minimise and to mitigate the mortality risk. Examining patterns of Barn Owl movement, and any influences upon, them can help to determine where such measures should be placed, in order to ensure that measures do not have unintended negative effects, for example by attracting birds to the vicinity of the railway line.
- The BTO’s ring-recovery database was used to analyse dispersal movements, with the aim of providing insight into national and, where possible, regional patterns in Barn Owl movements within the UK.
- Adult birds dispersed an average of 2.2 km between breeding sites, and 2.8 km throughout the rest of the year. Chicks dispersed further, making the bulk of their movements in the first few months after ringing, with evidence of initial forays further afield before settling closer to the natal site, an average of 7.8 km away.
- Further examination of dispersal distances indicated differences between the sexes, with female chicks dispersing further than males (although there was no difference for adults). In some instances, dispersal distance varied between regions; birds in the north west tended to disperse further than those in the south east. This pattern was not consistent across dispersal types, but it does show the potential influences of regional conditions.
- Dispersal distance appeared to be influenced by nearby habitat, with birds moving further through better quality habitat and to circumnavigate barriers, while habitats offering fewer resources tended to restrict movements.
- The results suggest that new, high-quality habitat aimed at mitigating negative effects of HS2 on Barn Owls should be located between 3 km and 15 km away from the railway route, depending on the importance placed on minimizing juvenile, as opposed to adult, mortality. Further, introducing barrier habitats may not be effective at restricting movements. Instead, locating poor quality foraging habitat near the railway line (or removing high-quality habitat) could help to minimise train strikes by restricting movements. However, this conclusion must be applied with caution because the results involved considered habitat only at large spatial scales. Nominally unsuitable habitat, such as intensive farmland, may actually include significant fine-scale habitat features that attract Barn Owls.
