S35.4: Raptors and grouse: A conflict in the uplands?

One of the most topical wildlife management issues in the British uplands concerns the relationship between raptors, particularly hen harrier Circus cyaneus and peregrine Falco peregrinus, and red grouse Lagopus lagopus scoticus (Etheridge et al. 1997; May 1997; Thirgood & Redpath 1997; Redpath & Thirgood 1997; Potts 1998). Raptors are of great conservation interest whilst red grouse are central to the economy of many private sporting estates. The illegal killing of raptors, which stems from concerns about their impact on grouse shooting bags, has generated much conflict between conservation and shooting interests. In this paper we present a brief overview of these interwoven conservation problems in the British uplands.

Heather moorland is one of the most distinctive habitats found in Europe and is considered to have appreciable conservation value (Thompson et al. 1995). Its global distribution is largely restricted to Britain and Ireland and its retention is a high conservation priority. There is evidence pointing to the loss of heather moorland to forestry and overgrazing by sheep and deer and much concern about this. The bird assemblage associated with heather moorland is considered outstanding in that there is a unique assemblage of arctic, boreal and temperate species. There are internationally important populations of raptors such peregrine, merlin Falco columbarius and golden eagle Aquila chrysaetos, and high densities of waders such as golden plover Pluvialis apricariea, curlew Numenius arquata and redshank Tringa totanus.

Large parts of Britain’s heather moorland resource are managed by private landowners for red grouse shooting. Heather moorland is thought to comprise about 25% of the British uplands and of that some 50% may by managed for red grouse - comprising about 7500 km² (Hudson 1992). The primary aim of grouse moor management is to maximise the number of birds available for shooting in autumn. To this end, gamekeepers are employed whose main tasks are to manage the heather and control predators (Hudson & Newborn 1995). Heather management entails burning in narrow strips to produce a mosaic of different aged stands of heather. Legally controllable predators include foxes and corvids but predator control has traditionally been extended to birds of prey, despite the fact that they have received legal protection since the 1950’s. Grouse shooting can be divided into two categories which broadly reflect the intensity of management and density of grouse produced. During ‘driven’ grouse hunters remain stationary in hides and beaters push birds toward the guns whilst during ‘walked-up’ grouse hunters walk the moor and shoot grouse as they are encountered. Driven shooting requires high densities of grouse usually in excess of 60 birds km² and can generate large bags and high revenues for estates.

Central to any debate about the management of raptors on grouse moors is the more fundamental question of whether or not grouse moor management is good for conservation. This question has received considerable attention in recent years, particularly in relation to the importance of grouse moors for upland breeding birds (Thompson et al. 1995; Brown & Bainbridge 1995). None of these studies is conclusive so far as indicating that a given area of moorland gains in either species richness or species abundance through having active management for red grouse. However, two general conclusions have emerged. First, if many moorland estates had not been managed for red grouse shooting they would have been afforested, resulting in widescale losses of habitat for moorland breeding birds. An analysis of land cover change in the Scottish uplands in relation to grouse management demonstrates that retention of grouse shooting was associated with lower rates of heather loss (Robertson & Barton ms). Second, widespread illegal persecution of raptors on grouse moors has resulted in a marked decline in the assemblage and abundance of birds of prey. We concentrate below on persecution of hen harriers, which is the cause of much recent controversy in the UK.

During the early 19^th century hen harriers were abundant and widespread and bred in both lowland and upland habitats. Loss of lowland habitat and persecution game shooting interests in the late 19^th century greatly reduced the breeding population and effectively eradicated it from mainland Britain (Watson 1977). With the decline in gamekeeping and the onset of bird protection legislation, harriers began to recolonise the UK mainland during the 1940’s and 50’s and reached their current distribution by the 1970’s. A survey in 1988 suggests that there are about 600 breeding females in Britain, with most found in Scotland (Bibby & Etheridge 1993). Harriers are still absent in large parts of uplands, particularly on the grouse moors of northern England.

What impact does human persecution currently have on hen harrier populations? Etheridge et al. (1997) studied the breeding productivity, natal dispersal and survival of hen harriers on moorland managed for red grouse, unmanaged moorland and young conifer forests in the Scottish uplands during 1988-95. Etheridge et al. found that breeding success of harriers was lower on grouse moors than elsewhere - 0.8 fledglings per female compared to 2.4 on unmanaged moorland and 1.4 in young conifer forests. Human interference at nests was recorded on half of the grouse moor estates and accounted for at least 30% of the breeding failures. Annual survival of female harriers on grouse moors was about half that on other moorland - and Etheridge estimated that at least 60 female harriers were killed each year. Losses of harriers on grouse moors would be unsustainable were it not for breeding in other habitats. In other words, grouse moors are a sink for the Scottish harrier population.

What effect do harriers and peregrines have on grouse populations and shooting bags? Here we summarise a five year research project at Langholm in southern Scotland (Redpath & Thirgood 1997) which addressed the following questions:

(1) What influences harrier and peregrine numbers on grouse moors?

(2) What influences harrier and peregrine diet on grouse moors?

(3) What effect does raptor predation have on grouse populations and shooting bags?

Having removed the effects of illegal persecution we found that the highest densities of hen harriers occurred on moors where passerines and voles were most abundant. Passerines and voles were most abundant on moors with a mosaic of heather and grass. This was an important finding as it suggests that in the absence of illegal persecution we would expect harrier densities to be highest on these grassy moors. Peregrine numbers tended to be more stable from year to year and we found no evidence that they were influenced by grouse density. By comparing peregrine nearest neighbour distances across a range of moors we found that peregrines bred at higher densities on southern moors, probably because there were more pigeons in these areas.

The rate at which harriers provisioned grouse chicks to their young varied considerably between different years and different moors. The main factor influencing this variation was grouse density with more grouse chicks resulting in higher grouse chick provisioning. The Type III functional response indicates that the greatest proportion of chicks will be removed at low to medium grouse densities. As with the harriers, the importance of grouse in the diet of peregrines increases with grouse density and the Type II shape of the functional response suggests that the greatest proportion of grouse will be removed at low grouse densities.

What were the effects of raptor predation on the grouse population? When raptors were abundant they killed on average 30% of the grouse overwinter, 30% of the breeding grouse in spring and harriers removed up to 40% of the grouse chicks produced by the surviving hens. Combining the adult grouse losses in spring with the grouse chick losses in summer suggested that raptors reduced autumn densities of grouse by 50%. What effect did this predation have on the shooting bags? We compared the grouse bags at Langholm where there were many raptors to those from two nearby moors where raptors were scarce. Between 1975 and 1993 the bags from all three moors cycled in synchrony. Since 1993, when raptor numbers at Langholm increased, grouse bags declined. In contrast, bags on the nearby moors increased to high levels. The simplest explanation was that raptor predation prevented the Langholm population from increasing to an expected peak.

Our data were strongly suggestive that raptor predation prevented the grouse population at Langholm from increasing to an expected peak. At these low grouse densities grouse shooting was not economically viable. The numbers of harriers and peregrines were high at Langholm because of the abundance of passerines and voles - and these alternative prey were abundant because of the mosaic of heather and grass.

Data on raptor diet suggested that the greatest proportion of grouse will be removed by harriers and peregrines from grouse populations at low grouse density. The implication of all these findings was that the impact of raptors will be greatest on low density grouse populations on grassy moors where raptors will be at high density.

Habitat management to reduce the amount of grass on moors may reduce the numbers of passerines and voles, thus leading to reductions in both harrier densities and their impact on grouse populations and shooting bags. Heather restoration through reduced grazing and improved muirburn would also bring other conservation benefits (Thompson et al. 1995). However, whilst certainly a worthy conservation objective, significant restoration of heather on moorland could take decades to achieve, by which time many grouse moors could be economically unviable if they stopped killing raptors. Direct intervention in the short-term may be needed on some moors to reduce predation on grouse. Two broad solutions have been suggested.

The first involves diversionary feeding of harriers with dead rats and poultry to attempt to reduce their predation on grouse. This approach is strongly favoured by government conservation agencies and is being trailed at Langholm during the 1998 summer. These trials will determine whether diversionary feeding harriers reduces predation on adult grouse in spring and grouse chicks in summer, and whether such feeding influences either harrier breeding densities or breeding success. A further consideration must be the financial cost and logistical constraints of feeding harriers and whether this method could be widely applied by gamekeepers.

The second approach, generally favoured by hunting organisations, is to set ‘quotas’ for hen harrier numbers, such that a given area of moorland only supports a set number of breeding harriers, with excess birds being prevented from breeding. It has also been suggested that harriers could be translocated from areas where they are at high density to suitable areas where they currently do not occur. The aim of such programmes would be to increase the national harrier population whilst limiting the local impacts that harriers can have on grouse populations, thus reducing the incentive for illegal control. Currently, direct intervention of this type is considered illegal under UK and European legislation and is strongly opposed by statutory and non-governmental conservation organisations.

It seems clear that such proposals should not be viewed as mutually exclusive. Combining capping of local harrier densities with diversionary feeding of the remaining birds could offer the best solution to this conflict. Such measures require the co-operation of conservation and shooting interests. The future of raptors, grouse, the moorland habitats they share and the rural communities they support depends upon it.

Many people contributed to this work but we particularly thank Ian Newton for his support. The study was funded by the Buccleuch Estates, Game Conservancy Trust, Game Conservancy Scottish Research Trust, Institute of Terrestrial Ecology, Joint Nature Conservation Committee, Natural Environment Research Council, Royal Society for the Protection of Birds, Scottish Natural Heritage and Westerhall Estate. SJT is grateful to the Royal Society for supporting his attendance at this conference.

Bibby, C.J. & Etheridge, B. 1993. Status of the hen harrier in Scotland in 1988-89. Bird Study 40:1-11.

Brown, A.F. & Bainbridge, I.P. 1995. Grouse moors and upland breeding birds. Pages 51-66 in D.B.A. Thompson, A.J. Hester and M.B. Usher, editors. Heaths and Moorlands: Cultural Landscapes. HMSO, Edinburgh.

Etheridge, B., Summers, R.W. & Green R. 1997. The effects of illegal killing and destruction of nests on the population dynamics of hen harriers in Scotland. Journal of Applied Ecology 34:1081-1106.

Hudson, P.J. 1992. Grouse in Space and Time: The population biology of a managed gamebird. Game Conservancy Trust, Fordingbridge, UK.

Hudson, P.J. & Newborn, D. 1995. Red Grouse and Moorland Management. Game Conservancy Trust, Fordingbridge, UK.

May, R.M. 1997. The hen harrier and the grouse. Nature 389:330-331.

Potts, G.R. 1998. Global dispersion of nesting hen harriers: implications for grouse moors in the UK. Ibis 140:76-88.

Redpath, S.M. & Thirgood, S.J. 1997. Birds of Prey and Red Grouse. Stationary Office, London.

Thirgood, S. & Redpath, S. 1997. Red grouse and their predators. Nature 390:547.

Thompson, D.B.A., MacDonald, A.J., Marsden, J.H. & Galbraith, C.A. 1995. Upland heather moorland in Great Britain: a review of international importance, vegetation change and some objectives for nature conservation. Biological Conservation 71:163-178.

Watson, D. 1977. The Hen Harrier. Poyser, Berkhamstead, UK.