• Hen Harrier Circus cyaneus nest sites on the Isle of Mull are associated with habitat mosaics and constrained by topography

      Geary, Matthew; Haworth, Paul F.; Fielding, Alan H.; University of Chester; Haworth Conservation Ltd. (Taylor & Francis, 2018-02-07)
      Capsule: Hen Harrier on the Isle of Mull, UK, are associated with habitat mosaics consisting of moorland, scrub and forestry but avoid grazed land, suggesting that forested habitats could be managed sympathetically for Hen Harrier in the future should the current UK population increase. Aims: To use distribution modelling to investigate nesting habitat associations using a long term dataset for Hen Harrier on Mull. Methods: We develop area-interaction models using a LASSO penalty to explore the distribution of 102 Hen Harrier nest sites in relation to habitat and topography. Our model is then successfully validated in tests using data for 70 nest sites from subsequent years. Results: Our model is effective in predicting suitable areas for Hen Harrier nest sites and indicates that Hen Harriers on Mull are found in habitat mosaics below 200 m asl. Hen Harrier nest intensity is positively associated with increasing proportions of moorland and scrub, open canopy forestry and closed canopy forestry. Nest intensity is negatively associated with increasing proportions of grazed land. Conclusion: Hen Harrier avoid grazed areas but are relatively tolerant of other habitat combinations. These findings are supported by previous observations of Hen Harrier habitat use and have implications for the recovery of some Hen Harrier SPA populations and future forest management. Open canopy forest and forest mosaics could potentially be incorporated into landscape-scale conservation plans for Hen Harriers using the population in Mull as an example.