Supporting Hen Harriers In Novel Environments

Hen Harrier Silhouette

Partners: University College Cork & BirdWatch Ireland
Funding Body: Department of Agricutlure, Food & the Marine
Duration: December 2017 - December 2019



Download advert here: Seasonal Fieldworker Vacancies 2018 


Project Background
Though widely distributed across the island of Ireland, hen harriers are scarce in this country with a current estimated breeding population of just 108-157 pairs in the Republic of Ireland in 2015 (Ruddock et al. 2016). Hen Harriers are Amber-listed in the Birds of Conservation Concern in Ireland, due to historical declines and continued vulnerability to habitat loss and persecution. They are also listed in Annex I of the EU Birds Directive, which is a legislative framework designed to protect birds, and includes measures such as the designation of Special Protection Areas (SPAs). Six Hen Harrier SPAs were designated in 2007 and these must be managed to maintain suitable habitat for hen harriers. Despite conservation efforts, there ihas been an estimated overall decline of 33.5% between 1998 – 2000 and 2015 (Ruddock et al. 2016). An intenstive study of breeding Hen Harriers undertaken at UCC bewteen 2007 and 2011 at three study sites in Ireland revealed that the number of breeding pairs in each area declined over the study period (Irwin et al. 2011) During this time, successive research projects at University College Cork have investigated the ecological requirements of Hen Harriers to inform their conservation management in an Irish context. This research has focussed on their breeding ecology in Ireland including aspects such as habitat selection, breeding biology and nesting ecology and the impact of land use change including afforestation and wind energy development.

In the absence of their traditional heather moorland and bog habitats, Hen Harriers in Ireland nest in young forest plantations with open canopies and strongly avoid grassland areas for nesting (Wilson et al. 2009). Hen Harrier breeding pairs in Ireland have a success rate of c63%, fledging an average of 2.6 young per nest (Irwin et al. 2008). During the breeding season, foraging adult female Hen Harriers hunt over distances of at least 7.5k, while their male counterparts travel at least 11km (Irwin et al. 2012). 

Hen harriers are typically open habitat birds but research at UCC has shown that they also use of forested landscapes in Ireland, particularly young forests during the first years after planting (Wilson et al 2010). However, this research has identified a conflict with maturing forests and areas of canopy closure in upland areas in Ireland within the hen harriers distribution (Wilson et al., 2006). Hen harriers in Ireland were subsequently recorded actively selecting recently planted forests for nesting (Wilson et al. 2009) which have been recorded as the most important nesting habitat in the most recent national hen harrier surveys (Ruddock et al., 2016). At one study area in Ireland a negative association between second rotation pre-thicket forest and breeding success was subsequently identified, which suggests that this species may be subject to an ecological trap (Wilson et al., 2012).

The distribution of Hen Harriers in upland landscapes in Ireland overlaps with areas of high value for wind energy development, which represents a further potential threat to their populations (Irwin et al. 2015). Recent studies have shown that evidence for a negative impact of existing wind farms on their populations is weak at present (Wilson et al. 2016), although proximity to turbines is associated with a slightly reduced breeding success (Fernández-Bellon et al. 2015).

Young, open forests are an important habitat for hen harriers in many areas where other natural habitats are degraded, and given the large numbers which now use these forests, finding an appropriate balance between forest management, industry priorities and conservation is key to the success of hen harrier populations.


This project aims to exploit large, archived datasets on hen harrier breeding ecology in Ireland, a large proportion of which has been collected by UCC as well as the latest 2015 survey data. We will investigate the relationship between hen harrier breeding success and forest management practises in the face of climate change.


Research Methods
Existing and new data will be used to examine whether variation in hen harrier breeding success is related to forest management practises. Two field studies will generate new data on previously identified knowledge gaps – the vulnerability of breeding hen harrier in different habitats to predators and the impact of clear felling debris (brash) within second rotation forests on habitat quality. We will also address three specific practical site-focused planning and management measures, identifying areas where forest removal will have the most impact, reviewing current pressures on hen harriers and conducting a meta-analysis of alternative mitigation measures to current Red Zones in place.

The findings of this study will be used to derive recommendations for the management of forest expansion in Ireland in relation Hen Harrier conservation.


Project Team

University College Cork:
Principal Investigator: John O'Halloran
Project Manager: Sandra Irwin
Post-Doctoral Researcher: Anthony Caravaggi 
MSc Student: Alan McCarthy

BirdWatch Ireland:
Researcher: John Lusby

Forest Ecology

Dept. of Zoology, Ecology & Plant Science, University College Cork, Distillery Fields, North Mall, Cork