Hen Harrier

Hen harrier monitoring report 2021

Under Article 4 of the Birds Directive (Directive 2009/ 147/EC) six Special Protection Areas (SPAs), covering a total land area of c.1,671km², are designated for the conservation of the Hen Harrier Circus cyaneus in Ireland.

Data from the 2021 hen harrier monitoring report has shown that Ireland’s population of hen harrier remains under threat in these SPAs. The report was released by the Hen Harrier Project which monitors the numbers of pairs of birds in the SPAs for the species during the annual breeding season. The total SPA population is now 25% smaller than at the time of designation.

A national survey of the species in 2015 estimated a breeding population of between 108 and 157 pairs – a decrease of 34% since the first survey in the 1990s. In 2021 there were 62 confirmed breeding pairs in the SPA network. Of the 62 confirmed breeding pairs in 2021 just 18 pairs (30%) were found to have successfully reared and fledged a total of 34 chicks. The fledging rate is the lowest recorded to date, below levels required for a self-sustaining population.

The Stacks, Mullaghareirks, Mount Eagle and West Limerick Hills SPA holds the largest population in the SPA network, but the population has declined by a third since 2005. There was an 80% failure rate from the 32 confirmed nests in 2021, with only eight pairs successfully fledging a total of 19 young.

Overview of hen harrier breeding population in SPA network in 2021:

  • Mullaghanish to Musheramore SPA – 3 confirmed pairs; 6 young
  • Slieve Aughty Mountains SPA – 7 confirmed pairs; 4 young
  • Slieve Beagh SPA – 3 confirmed pairs; 2 young
  • Slieve Bloom Mountains SPA – 10 confirmed pairs; 0 young
  • Slievefelim to Silvermines SPA – 5 confirmed pairs; 3 young
  • Stack’s to Mullaghareirk Mountains SPA – 34 confirmed pairs; 19 young

Main threats and pressures on hen harrier breeding populations:

There are several factors that influence nest success including habitat quality, loss and fragmentation of habitat, poor weather and disturbance leading to nest abandonment. The monitoring report lists predation as a possible cause of breeding failure in four of the six SPAs.

In the Slieve Aughty Mountains SPA, direct and indirect effects of habitat loss and fragmentation and predation were identified as significant factors in the breeding population halving since 2005.

Burning of moorland also hinders the birds, because they breed in open, upland habitats, using heather, pre-thicket forest plantations, or scrub, for nesting, while feeding on small birds and mammals. The Slieve Beagh SPA suffered extensive burning causing a pair to abandon their territory in 2021

Hen harriers prey on small birds and mammals and another factor in their decline could be the loss of food sources in the areas they inhabit.


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