Hen harrier

The hen harrier is identified as a species of high conservation concern in Ireland and the UK and is protected in Ireland under the Wildlife Act 1976 & Amendment Act 2000 and in Northern Ireland under The Wildlife (Northern Ireland) Order 1985. With its breeding population having declined by more than 50% in the past 30 years the Hen harrier is listed as an Annex I species under the EU Birds Directive (1979) and accordingly has a high conservation status. Annex I refers to a list of species that require strict protection due to their populations declining seriously throughout their respective ranges. The EU Birds Directive provides a legislative framework of measures required to assess and ensure the conservation status of the Hen harrier, this includes monitoring, research and the designation of Special Protection Areas (SPAs).Under Article 4 of the Birds Directive (1979), it is required that, outside of designated SPAs, each State must strive to ‘avoid pollution or deterioration of habitats’ of all wild birds, including all species listed in Annex I of the Directive’.

Female hen harrier

Female hen harrier

Hen harrier populations had dramatically dropped by the 1950’s in Ireland and was considered rare. However, individual sightings persisted and records of Hen harrier breeding in the Slieve Bloom Mountains in Co. Laois and on the Waterford/Tipperary border were recorded. From the early 1950’s and increase in Hen harrier breeding was noted with the population in Ireland rising to an estimated 200-300 pairs by 1972; this was possibly due to an increase in coniferous forestry plantation. However, from the mid-1970s to the early 1980’s populations again declined dramatically. This has been attributed to the maturation of coniferous plantations and the intensification of agricultural land use with land reclamation and drainage under the Arterial Drainage Act, hedgerow removal and scrub clearance under the Common Agricultural Policy (CAP). Population decreases through these decades have been linked to habitat loss and deterioration, nest destruction, predation and persecution; however, habitat loss is identified as the most significant due to irreversibility.

The results of the 2010 Republic of Ireland hen harrier survey were published in March, 2012. This study identified that a majority of confirmed nests/territories within Hen harrier SPAs during the 2010 survey were located in afforested habitats (57%), primarily in second rotation crops (43.8%) and more frequently than in open moorland (heather) habitats (23.4%).

The number of breeding pairs of hen harriers found during this survey is similar to that found by the last national survey in 2005 despite over twice the field effort recorded during 2010. The overall number of confirmed breeding pairs at a national level has decreased marginally (132 to 128), but the number of possible breeding pairs has apparently increased (21 to 44 pairs). Whilst it is conceivable that the population remains comparatively stable, the increase in field effort means that a larger number of ‘extra’ pairs may have been located during 2010. This raises the possibility that there has actually been a decrease between the two surveys.

The breeding range of confirmed pairs has remained within approximately the same number of 10km squares (53 squares) since 2005 although these differed between survey years. Areas where losses of breeding pairs appear to have been particularly severe include the Stack’s / Glanarudderies / Knockanefune / Mullaghareirks / North of Abbeyfeale complex and the Slieve Aughties. The role of habitat changes such as forest maturation; constrained breeding success; disturbance; prey availability; displacement by wind‐farms and/or disturbance and land management or loss of open moorland habitats require further investigation in these areas.

Male hen harrier

Male hen harrier

Forest maturation, may be partly responsible for regional decreases in breeding hen harriers, as a shift in age structure of plantations was recorded between the two surveys with a general increase in older classes of suitable forest breeding habitats. Notably, whilst the proportion of older plantation increased considerably in the Stack’s Complex, the lowest decline in availability of 2-5 and 6-9 age classes was recorded. A decrease in the availability of suitable breeding (i.e. nesting and foraging) habitat may therefore have contributed to decline of the hen harrier population in this area.

Importantly hen harrier populations in the Stack’s to Mullaghareirk Mountains, West Limerick Hills and Mount Eagle SPA has declined by 35.6% and the combined population protected within all the SPAs has decreased overall by 18.1%.  This site is in one of the two areas of largest regional declines; namely the Stack’s / Glanarudderies / Knockanefune / Mullaghareirks / North of Abbeyfeale complex and the Slieve Aughties. The hen harriers in the Stacks SPA (and the Slieve Aughties) exhibited greatest preference for forest nesting than hen harriers in other SPAs and are therefore most likely to be affected by changes in the forest age structure and/or variation in breeding success associated with forest habitats.

Hen harriers often appear to hunt transiently through forest environments en route to open moorland/rough grassland, often utilising tracks and fire breaks. These observations are supported by data on the diet of harriers, which consists largely of moorland prey, such as meadow pipit and skylark. Many nests, in Ireland appear to be several kilometres from the nearest moorland and as such, may considerably increase foraging ranges.

Disturbance threats to hen harriers and suspected causes of nest failure were reported by fieldworkers at 56 territories (n = 68 individual records). The highest apparent failure rates occur where burning (most significant), turf‐cutting, vehicular disturbance, forestry operations and/or predation are recorded. Records of disturbance at hen harrier territories associated with turf‐cutting and windfarm(s) were recorded most frequently in Co. Monaghan and the south‐west respectively. There were notably high rates of failure in the Stacks to Mullaghareirks etc. SPA resulting from all of the above, with particular reference to forest maturation. Predation and/or predation risk was attributed to four species, namely fox, pine marten, hooded crow and mink.

Male hen harrier

Male hen harrier

From the literature available to date it is concluded that hen harriers will continue to utilise wind energy sites for foraging, with a displacement distance of 250m recognised from literature available. Hen harriers have been recorded flying at low elevations during foraging, with Hen harriers which occupy and forage within wind farm sites observed displaying very high avoidance rates, in the region of 99%. The risk of collision with ancillaries including power lines, fences, guy wires, etc. is identified as an associated cumulative impact.  The passage of Hen harriers through windfarms is not the primary concern, where the potential impacts of greatest importance are those on foraging success and breeding productivity. Hen harrier nesting may be displaced by wind energy developments by up to 500m, with an overall reduction of hen harrier activity within this area.

Ecofact ornithologists are experts in providing both surveys and impact assessments in relation to hen harriers. Please contact us to disucss your wind farm bird survey rerquirements.

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