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Hen Harrier Circus cyaneus ecology and conservation during the non-breeding season in Ireland

ABSTRACT Capsule A total of 203 Hen Harrier Circus cyaneus winter roosts was recorded in Ireland between 2004 and 2020. The main habitat used for roosting was heath/bog. Burning and land-use change including forestry, agriculture and renewable energy were the most frequent among various pressures and threats recorded. Aims To find and survey Hen Harrier roosts and establish the distribution and habitat associations during the non-breeding season, as well as the conservation issues facing the species during that time. Methods Surveys were undertaken across Ireland each winter from 2004 to 2020, searching for roosts and recording occupancy, behaviour, roost characteristics, pressures and threats. Satellite tracking was also used to locate roosts. Results A total of 203 roosts was recorded, with a widespread distribution. Heath/bog was the most frequently used habitat (53% of roosts), while 53% of roosts were located at less than 100 m above sea level. More than half (52%) of the roosts were communal. The median number of Hen Harriers per roost was 2, the average number was 2.5 and the maximum recorded was 16. Almost a third (31%) of sites documented by this long-term study have become inactive due to anthropogenic pressures. Primary pressures and threats included the disturbance/removal of roosts (e.g. through burning and wind farm development) and changes to the surrounding landscape (e.g. agricultural intensification and afforestation). Conclusion Identifying the distribution, roosts and habitat use of Hen Harriers during the non-breeding season, as well as the prevalent threats and pressures, provides a solid platform on which to base necessary conservation action in Ireland. Supporting landowners to maintain or improve habitats, and taking account of roosts and hunting grounds in assessing proposed developments/land-use change should be considered in any conservation strategy for Hen Harriers.