Why Merlins Do Better Where Gamekeepers Work

In summary

• Merlins nest mainly on the ground in heather, leaving eggs and chicks exposed to predators.

• At Langholm, merlin breeding success was two to three times higher under grouse moor management.

• Nearly 88% of British merlin breeding areas were recorded across five moorland types.

• Britain holds roughly 1,100 breeding pairs, with open moorland the core breeding habitat.

The merlin is a bird most people never see. Britain's smallest falcon is barely bigger than a mistle thrush, hunts low and fast over open ground, and spends its breeding season in some of the emptiest country we have.

It is also a bird whose fortunes are bound up, more tightly than almost any other raptor, with what happens on heather moorland.

A falcon that nests on the ground

Most falcons nest on cliffs or take over old crow nests in trees. The merlin, in Britain, mostly doesn't. It nests on the ground, in deep heather.

The scale of that preference is striking. A national survey analysing more than 1,000 merlin nest records found that 87.5% of breeding areas were in five moorland types — dry heather moor, mixed wet-dry heather moor, wet heather moor, grass moor and mixed grass-heather moor — with 77% of nests on the ground in heather, 19% in old stick nests in trees and just 2% on crags.

A long-running study in the Lammermuir Hills found the pattern even more pronounced: over 96% of nests were on the ground in heather.

This explains a lot of what follows. A merlin nest is reachable by a fox. It is findable by a crow. Whatever else determines whether merlins succeed in a given landscape, ground predators are near the top of the list.

What happened at Langholm

The most useful evidence on this comes from a 27-year study at Langholm Moor in southwest Scotland, where grouse moor management stopped and later restarted — creating something close to a natural experiment.

The findings were clear. Ground-nesting raptors — hen harrier and merlin — increased during periods of grouse moor management and had a higher proportion of successful nesting attempts.

Breeding success for both species ran two to three times higher when the moor was managed for red grouse, with predation identified as the main apparent cause of nesting failure.

The reason is straightforward. When the moor was keepered, average abundance indices during the breeding season were 65% lower for foxes and 62% lower for carrion crows. Fewer ground predators, more merlin chicks fledged.

Two details make this study hard to wave away:

• The contrast was specific to ground-nesting species. Management made no difference to the abundance or breeding success of tree- and crag-nesting raptors — peregrine, buzzard and raven. That's exactly the pattern you'd expect if nest predation is the driver, and it's a strong argument against the result being a coincidence.

• The paper is co-authored by scientists from the Game and Wildlife Conservation Trust and the RSPB Centre for Conservation Science, and published open-access in a peer-reviewed journal. It isn't a partisan document.

The threat of losing the open hill

For merlin, the clearest long-term risk is the disappearance of open moorland altogether.

Merlins need a lot of open ground. Work in southwest Scotland estimated that a minimum of around 20 km² of grass and heather moorland within a mosaic of roughly 60% moorland and 40% forest is needed for territories to remain viable. In Wales, the figure suggested was 70–80% open moor adjacent to nests.

Blanket afforestation is the pressure that attacks those thresholds. Plantations may occasionally offer nest sites, but they reduce the open foraging habitat merlins depend on. A hill that is planted, improved or scrubbed over is a hill without merlins — regardless of who manages it or how.

Why this matters

The merlin is a reminder that ground-nesting birds live or die by what walks the moor at night: keep the hills open and keep predator numbers in check, and Britain's smallest falcon has somewhere to raise its young.