When is the last time you saw a hen harrier?

Dick Warner notices that hen harriers seem to be much rarer these days

It’s a long time since I’ve seen a hen harrier. I used to see them quite often. When I lived in Co Waterford I’d watch them hunting over the Comeragh mountains in summer and in winter they’d quite often turn up on the coast, sometimes flying past the bottom of our garden. Even when I moved to Co Kildare, which is not prime harrier habitat, I’d see them fairly frequently patrolling the headlands of bogs in winter. But all that was some time ago and today they’re much rarer.

This is a shame because they must be our most elegant bird of prey, given the skill with which they fly on those long wings and their remarkable owl-like faces. I particularly miss seeing the males with that amazing pearl grey plumage.

The hen harrier is an Annex One species under the EU Birds Directive. This means that Ireland is legally obliged to protect them. So in 2007 we created six Special Protection Areas in upland habitat where they were known to breed. This was not popular with some sheep farmers who felt that it restricted their ability to develop their land and devalued it. It also, unfortunately, seems to have failed to halt the decline in harrier numbers.

They were persecuted in the 19th and early 20th centuries when guns became more efficient and more widespread, and when all birds of prey tended to be regarded as vermin to be exterminated. But this changed and harrier numbers began to rise, reaching between 200 and 300 breeding pairs by the 1970s — not big numbers but a viable population. But then things started to go wrong.

The first proper survey was in 1998-2000 and there have been three more since, the last one carried out in 2015. It was the most comprehensive of the four but only found between 108 and 157 breeding pairs. This represents a decline of 33.5%, a third of the population, in 15 years.

So what’s the problem? Persecution is no longer a major factor. It seems to have more to do with changes in their upland breeding habitat. Other species that breed in the same habitat, such as curlews and red grouse, are suffering similar declines. Wind farms could be a factor, although this isn’t easy to prove. The most likely culprit is forestry plantations.

Apparently when a conifer plantation is first established on a heather-covered hillside it suits hen harriers. They are ground nesting birds and will often move their nest site from deep heather into the young trees. The establishment of the plantation can also increase their food supply by providing habitat for small mammals and birds. But after about 10 years when the trees have grown big enough to touch each other it becomes impossible for the harriers to cope. And 20th century forestry is now maturing without any economic incentive to fell and replant it.