Duration: 2012 – 2014

Background:
The Hen Harrier is an Annex 1 listed species afforded protection under the EU Birds and Habitats Directives that is found sparsely distributed across ireland. Researchers at University College Cork have examining the relationship between Hen Harriers and land-use change since 2000. This study on Hen Harriers and wind farms was focused on expanding the knowledge base on Hen Harrier ecology and windfarm interactions in an Irish context, to provide evidence based data for policy makers, industry and other stakeholders. The 30 month study was undertaken at University College Cork School of Biological, Earth & Environmental Science under the leadership of Professor John O’Halloran.

Project Objectives:
The aim of this project was to provide scientific support for strategic planning for the development of the wind energy sector in an environmentally sustainable manner, while ensuring the conservation interests of the Hen Harrier are protected. Members of the Irish Wind Energy Association (IWEA) the national association for the wind industry in Ireland provided financial support for this study.

Project Findings:
The primary conflict between wind energy development and Hen Harrier conservation is the large spatial overlap between these competing resources. Of the 69 survey squares across Ireland where breeding Hen Harriers were recorded in 2010, this study found that 28% of squares coincided with one or more wind energy developments by 2012. A weak negative relationship was identified between wind farm presence and the observed change in the number of breeding Hen Harrier pairs in survey squares between 2000 and 2010. However, the available evidence suggests that this was not a causative relationship.

Prey availability is an important factor in mediating the effects of land use change on Hen Harrier populations and, in this study, densities of small birds on which Hen Harrier prey were lower at wind farm study sites than at control sites and lower closer to turbines (within 100m) at wind farm study sites than further away. The particular species of bird that were impacted by wind farm development was dependent on the existing habitat at the site and the extent of the area affected by modifications related to wind farm construction.

The impacts of land use change are often mediated through impacts on foraging success, which was investigated during this study using novel GPS tags combined with traditional vantage point watches. The findings highlight the importance for Hen Harriers of open habitats suitable for foraging and the selection of foraging habitats by Hen Harriers differed between wind farm and control study sites. Although the availability of open and young forested habitats was similar at all study sites, the use of forested areas was lower around wind farms relative to control study sites.

Impacts of wind farms on either prey availability or hunting efficiency may ultimately impact on birds through effects breeding success and so this study also examined the breeding performance of Hen Harrier pairs in Ireland in relation to wind energy development. Three measures of breeding performance (nest success, fledged brood size and productivity) were used and no statistically significant relationships with distance to wind turbines were found. However, lower nest success rates were recorded within 1km of turbines which, although not statistically significantly different to nest success rates further away from turbines, may be of biological relevance and cannot be ignored. Where nests within 1km of wind turbines were successful, their fledged brood sizes were not different from those nests further away from turbines.

Birds are at risk of collision with wind turbines only when their flight path overlaps with the rotor blade sweep area of a wind turbine and in the current study, adult Hen Harriers were seen to spend 12% of their flight time at wind farms at turbine rotor sweep height and this did not differ between wind farm and control sites. The amount of time spent flying at this height by newly fledged Hen Harriers close to the nest was negligible (<1%). Using conservative estimates, collision risk analysis revealed that, over the life time of a typical wind farm in Ireland (25 years), the number of Hen Harrier deaths resulting from collisions with wind turbines is estimated to be in the range of 0.8 to 2.5 birds. These findings demonstrate that Hen Harriers are at low risk of collision with wind farm infrastructure as a result of their typically low flight height and known avoidance behaviour.

This study makes a significant contribution to the body of knowledge on the interaction between wind farm development and Hen Harriers in Ireland and provides high quality scientific evidence to support the formulation of policy and practice. This is the first study of this kind in Ireland and further investigations will be required, when further data become available, to understand more fully the effects involved.

Publications: 

• Fernández-Bellon, D., Wilson, M.W., Irwin, S. and O’Halloran, J. 2018. Effects of development of wind energy and associated changes in land use on bird densities in upland areas. Conservation Biology, 33(2): 413-422. ConservationBiology2018
• Wilson, M.W., Fernández-Bellon, D., Irwin, S. and O’Halloran, J. 2016.  Hen Harrier Circus cyaneus population trends in relation to wind farms. Bird Study, 64:20-29. Wilsonetal2016
• Fernández-Bellon, D., Irwin, S., Wilson, M.W. and O’Halloran, J. 2015. Reproductive output of Hen Harriers Circus cyaneus in relation to wind turbine proximity. Irish Birds, 10: 145-150. FernandezBellon2015

Final Project Report: 

• WINDHARRIER Report

For further information on this project please contact Prof. John O’Halloran.