Sir

We read with interest articles by May1 and Mead2 on the persecution of hen harriers and the impact of raptor predation on grouse-shooting bags. Some of Mead's comments, however, are misleading2.

Mead suggests that the economic effects of harriers on grouse shooting are minimal. Unfortunately, that is not always the case. We recently completed six years of research on harrier and peregrine predation on grouse at Langholm in southwest Scotland3. Raptors had bred freely on this moor since 1990, and female harrier numbers increased from two to twenty between 1992 and 1997. Peregrine numbers increased from three to six pairs.

When raptor numbers were high, they removed 30% of breeding grouse in April and May and harriers removed 37% of the grouse chicks between June and August. Most of these losses appeared to be additional to other mortality, and we estimated that they reduced post-breeding numbers of grouse by 50%.

Historically, grouse bags at Langholm have shown a six-year cycle, peaking last in 1990, with 4,038 grouse shot (Fig. 1). Since 1990, grouse bags have declined, with 51 birds shot in 1997.

Figure 1: Numbers of red grouse shot on Langholm moor during 1975-97 in comparison with numbers shot on nearby moors F and G during the same per.
figure 1

iod. Grouse bags on all three moors fluctuated in synchrony from 1975 to 1993. After 1993, grouse bags on moors F and G increased while bags on Langholm moor continued to decline. Harrier and peregrine numbers on Langholm moor increased between 1992 and 1997 whereas the numbers of these raptors on moors F and G remained low.

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In contrast, grouse bags on two nearby moors, with low raptor densities, having previously fluctuated in synchrony with Langholm moor, increased to high levels in 1997.

Increased predation by raptors at Langholm was considered the most likely cause for low grouse bags. Grouse management at Langholm cost £99,500 (US$168,000) in 1997 and, with grouse shooting producing £40 per bird, a bag of 2,487 grouse was required to balance costs. Clearly, if bags remain low the economic cost will be considerable.

Mead2 suggests that more red grouse are killed on deer fences than are taken by harriers, citing work in Highland Scotland4.

There are several flaws in this argument. First, deer fences are uncommon in red grouse range outside the Highlands, and indeed on many Highland moors. For example, there is little fencing at Langholm and collisions account for fewer than 1% of all recorded deaths3. Second, Highland studies5 suggest that 11% of red grouse deaths are due to collisions but 48% are due to raptor predation. Third, fences pose fewer problems to red grouse than to woodland grouse as strikes are concentrated near young plantations4 and red grouse are birds of open moorland.

Finally, how can conflicts between raptors and grouse shooting be resolved1? As suggested by Mead6, predation patterns observed at Langholm will not apply everywhere. Our data suggest that, in the absence of persecution, harrier numbers will be related to densities of prey other than grouse3. In the long term, reducing the amount of grassland on moors may reduce the numbers of songbirds and voles, leading to reductions in harrier density and reducing their impact on grouse populations.

In the short term, however, raptor-grouse problems may require more active intervention in the form of supplementary feeding or raptor translocation. Such measures require the cooperation of conservation and shooting interests. The future of raptors, grouse, the moorland habitats they share and the rural communities they support depends upon it.