Delicate balancing act

GROUND-NESTING raptor species showed higher levels of breeding success when Langholm moor was managed for grouse shooting.

A newly-published study, undertaken as part of the Langholm Moor Demonstration Project, has shown that the legal management of heather moorland for red grouse shooting may benefit some raptors by reducing predation risk and increasing food availability for them.

But it concluded that, on a UK scale, the benefits delivered through grouse moor management are currently outweighed by the negative impacts of illegal killing of hen harriers.

The study examined data gained over a 27-year period on Langholm Moor, including 10 years from 2008 to 2018 as the Langholm Moor Demonstration Project.

It considered changes in abundance and breeding success of four raptor species and of raven in relation to whether the moor was being actively managed for grouse shooting.

The study established that the ground-nesting hen harrier and merlin increased during periods of management, with a higher proportion of successful breeding attempts because of reduced nest predation, a major factor affecting breeding success.

However, management did not influence the abundance of the tree-nesting or crag-nesting species of peregrine falcon, common buzzard and raven or their breeding success.

Sonja Ludwig is the senior scientist with the Game & Wildlife Conservation Trust who did the work for the Langholm Moor Demonstration Project.

She said: “On moors managed for driven grouse shooting gamekeepers routinely remove generalist predators, including foxes, stoats, weasels and carrion crows to increase post-breeding red grouse densities.

“This management has been shown to also improve breeding success and abundance of other ground-nesting birds such as waders and some passerines.

“Nest predation can be an important cause of breeding failure in some raptors, with nests on the ground being more vulnerable to mammalian predators than those in trees or on other elevated structures.

“Long-term monitoring is essential when assessing fluctuations in breeding populations in response to environmental changes.

At Langholm we were able to study how changes in management affected breeding success and abundance of raptors and raven over a period of 27 years.

“During this time grouse moor management was withdrawn, reintroduced and withdrawn again.

“The results of our study highlight that, in the absence of illegal persecution, grouse moor management can benefit ground-nesting raptors such as hen harrier and merlin.”

Professor Des Thompson, is Scottish Natural Heritage’s principal adviser on science and biodiversity.

He said: “It’s good to see more work published from the long-term Langholm project and this interesting paper shows that even ground-nesting raptors can succumb to predation.

“However, it’s important to note the conclusion on the negative impacts of the illegal killing of hen harriers which, for us, remains a significant concern.”

Reference to paper: Ludwig SC, Roos S, Rollie CJ, Baines D (2020), Long-term changes in the abundance and breeding success of raptors and ravens in periods of varying management of a Scottish grouse moor.

Avian Conservation and Ecology 15 (1): 21 www.ace-eco.org/vol15/iss1/art21/