Project Title: Optimum scenarios for Hen Harrier conservation in Ireland (HENHARRIER)
Partners: University College Cork
Funders: Department of Agriculture, Food and the Marine (DAFM) & National Parks and Wildlife Service (NPWS)
Duration: 2007 - 2012


Hen Harrier (Circus cyaneus) numbers in Ireland have shown considerable fluctuation over time. They were once widespread across Ireland, but by the early 20th Century their population had reached critically low numbers through a combination of habitat degradation and persecution. Their population increased again to an estimated 250 - 250 breeding pairs by the 1970s, an increase which has been linked to the establishment of new forest plantations. Although traditionally birds of open habitats, Hen Harriers can use young forest plantations while the trees are very small. In some areas the subsequent maturation of these forest plantations has coincided with local extinctions. National surveys of Hen Harrier populations have been undertaken every 5 years since 2000 and have shown that Hen Harrier numbers have once again steeply declined, particularly in some heavily forested areas.

Hen Harriers are now an Annex 1 species on the EU Birds Directive. This Directive requires that all member states, including Ireland, take measures to ensure the persistence of Hen Harriers through the designation of Special Protection Areas (SPAs), within which appropriate steps must be taken to provide and maintain suitable habitat for Hen Harriers.

Habitat change is the biggest single factor implicated in the decline of Hen Harriers. Traditionally birds of open heathers and moors, they depend on open habitat for both foraging and nesting. Afforestation of open habitat renders it unsuitable for Hen Harriers, although they have been shown to use conifer plantations for hunting and nesting during the early stages of forest growth before canopy closure. In the first years following planting young conifer plantations are structurally similar to open scrub habitat.

Special Protection Areas (SPAs) have been designated by the Irish government for the protection of this species, all of which include suitable Hen Harrier breeding habitat such as heaths and bogs, rough grassland and young conifer plantations. These SPAs must be managed in order to ensure the provision of suitable habitat in the face of future developments and land use change in order to ensure the stability of the Hen Harrier populations that they support. However, even without further changes in land use, maturation of forests in these SPAs over the next decade will result in a substantial decrease in the proportion of suitable Hen Harriers habitat.

Further information on the habitat requirements of Hen Harriers in Ireland is required in order to ensure that this species can be adequately provided for within the designated SPAs. To this end, this project was undertaken to increase our knowledge of Hen Harrier breeding biology and habitat requirements to inform conservation management of the species in Ireland. This project comprised both field and desk studies of Hen Harrier foraging and breeding ecology over a period of five years.


Between 2007 and 2011 detailed data was collected on Hen Harrier breeding ecology in four study areas in Ireland using a range of appropriate methodologies including direct observations, nest cameras, GPS tags, pellet analysis and wing-tagging of juveniles. All four study areas include a matrix of different habitat types including first and second rotation conifer plantations. The study sites in the Slieve Aughty Mountains and in Kerry are designated Hen Harrier SPAs, while the other two study sites hold relatively dense concentrations of breeding Hen Harriers. 


Hen Harrier Study Sites 


Research Findings:

This project provided detailed scientific data on Hen Harriers that is essential if Ireland is to meet its obligations to protect Hen Harriers and their habitats under the EU Birds Directive, which can only be achieved with the support of appropriate policies and management practices. A number of recommendations were made, addressing different aspects of policy, management and priorities for future research.


During this study, Hen Harriers breeding performance in some parts of Ireland appeared to be sufficient to allow populations to persist in these areas. However, some populations, particularly in the south west of Ireland, declined markedly during the study period. Into the future, careful targeted management is required to ensure their long-term reproduction and survival.


Many areas of suitable Hen Harrier habitat (open heather and moorland) have historically suffered serious declines in Ireland, and Hen Harriers have subsequently been seen to use the relatively open areas of young forest plantations where this is available to them. A detailed study of this behaviour showed that Hen Harriers actively select nest sites in young forest plantations in Ireland, relative to other available habitat. However, at least in some areas, the value of this habitat for Hen Harriers is questionably, due to its association with high rates of breeding failure, possibly due to increased levels of nest predation. As plantation forests mature their utility for breeding or foraging Hen Harriers decreases. Despite this, no negative relationship between breeding success and cover of either closed canopy forest or all forested areas was demonstrated in any of study areas during this project. These findings suggest that conventionally managed commercial forest plantations can be suitable for Hen Harrier nesting and foraging during the first one third to one quarter of the forest rotation. Afforestation of open habitats that are currently suitable for Hen Harriers would therefore greatly reduce the value of those areas for Hen Harriers in the long term. However, afforestation of areas not currently of value to Hen Harriers could increase the area of suitable habitat, provided that these young forests are managed in a way that doesn't contribute to reduced breeding success of Hen Harriers.There is scope to build on this significant body of work in the future to provide a more thorough understanding of Hen Harrier population ecology in Ireland, particularly in light of the continued land use and climate change. The challenges that we face in this regard include improving our understanding of the role of habitat quality in breeding success, the interaction between breeding and roosting populations, the fate of fledged young and the source of breeding populations. Also of particular interest is the investigation of factors important to Hen Harrier populations in the changing land use of the future.


Further Information:
Detailed information on these findings can be found in the HENHARRIER Final Project Report.

Please contact Prof. John O'Halloran (j.ohalloran@ucc.ie) for further information.


This project included research towards one PhD thesis, carried out by Barry O'Donoghue, and also supported by the National Parks and Wildlife Service.



  • Wilson, M.W., O'Donoghue, B., O'Mahony, B., Cullen, C., O'Donoghue, T., Oliver, G., Ryan, B., Troake, P., Irwin, S., Kelly, T.C., Rotella, J.J. & O'Halloran, J. 2012. Mismatches between breeding success and habitat preferenes in Hen Harrier Circus cyaneusbreeding in forested landscapes. Ibis, 154: 578-589.
  • Irwin, S., Wilson, M.W., Kelly, T.C., O'Mahony, B., Oliver, G., Troake, P., Ryan, B., Cullen, C., O'Donoghue, B. & O'Halloran, J. 2011. The breeding biology of Hen Harriers Circus cyaneus in Ireland over a five year period. Irish Birds, 9: 165-172.
  • Wilson, M.W., Irwin, S., O'Donoghue, B., Kell, T.C. & O'Halloran, J. 2010. The use of forested landscapes by Hen Harriers in Ireland. COFORD Connects, Environment No. 10.
  • Wilson, M.W., Irwin, S., Norriss, D.W., Newton, S.F., Collins, K., Kelly, T.C. & O'Halloran, J. 2009. The importance of pre-thicket conifer plantations for nesting Hen Harriers Circus cyaneus in Ireland. Ibis, 151:332-343
  • Irwin, S., Wilson, M., Kelly, T.C., O'Donoghue, B., O'Mahony, B., Oliver, G., Cullen, C., O'Donoghue, T. & O'Halloran, J. 2008. Aspects of the breeding biology of Hen Harriers Circus cyaneus in Ireland. Irish Birds, 8: 331-334.


Image Bar Hen Harrier

Planning and Management Tools for Biodiversity in a Range of Irish Forests

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