Hen harriers: Illegal killing the main cause of death for one of the UK’s most at-risk birds

The study, led by the RSPB, also found that mortality due to illegal killing was highest in areas managed for red grouse shooting.

Using data from what is said to be the largest GPS tracking programme for hen harriers globally, the authors discovered that individuals tracked by the project were typically living for just 121 days after fledging.

They also found that a 10 per cent increase in grouse moor use by the birds was associated with a 43 per cent increase in the mortality rate.

It comes after conservationists in the Yorkshire Dales described how they found the body of a hen harrier mutilated on a grouse moor.

The bird found had been a Natural England tagged hen harrier named Free, and expert veterinary assessment concluded the bird has been killed through traumatic removal of its head and leg, whilst alive.

The police carried out a search warrant in connection with the incident, but the ensuing investigation failed to lead to charges.

Twenty other harriers, including 15 birds that were part of satellite-tagged tracking projects, have also disappeared across Northern England in the past year.

Steven Ewing, RSPB senior conservation scientist and lead author of the study, said: “Hen harriers have been legally protected for almost 70 years, but this study adds to the already overwhelming evidence base that illegal killing on grouse moors remains a key cause of this species’ low population size and its ongoing absence from large areas of the uplands, particularly grouse moors.”

The RSPB said despite all birds of prey being protected by law since the 1950s and more recently under the Wildlife and Countryside Act 1981, illegal persecution is still known to be a serious issue.

Hen harriers are on the red list of birds of conservation concern in the UK, meaning they are one of the most at-risk species here.

Their stronghold is in Scotland where about 70 per cent – 80 per cent of the UK breeding population of hen harriers are found, mostly in Orkney and the Hebrides.

For the new study, published in the journal Biological Conservation, researchers used satellite tracking devices to look into the survival and movements of hen harriers.

Between 2014 and 2020, the RSPB and partners fitted satellite transmitters to juvenile hen harriers at nests across Scotland, England, Wales and the Isle of Man.

Tags were deployed on 148 individuals, 86 of them in Scotland, funded by the Hen Harrier Life project.

The scientists looked at survival rates, causes of death whether natural or through illegal killing, and associations between mortality and land managed for grouse shooting.

Annual survival was low, especially among birds under one year, with illegal killing accounting for the deaths of 27 per cent – 41 per cent of birds under one year, and 75 per cent of mortality in birds aged between one and two years.

Not enough birds survived more than two years to estimate mortality due to illegal killing of adults.