New study published in an important scientific journal shows yearly survival rates of Hen Harriers are ‘unusually low’ with birds typically living just four months after fledging the nest.
Illegal killing is the main cause of death in Hen Harriers over one year of age and a major cause of deaths in birds under one year according to a new paper, published in the journal Biological Conservation, and led by the RSPB. Using data from the largest GPS tracking programme for Hen Harriers globally, the authors discovered that individuals tracked by the project were typically living just 121 days after fledging. The risk of dying as a result of illegal killing increased significantly as Hen Harriers spent more time on areas managed for grouse shooting.
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. 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.
In 2011 the UK Government published the authoritative Conservation Framework for Hen Harriers which identified illegal killing of this species as the primary cause stopping population recovery. A 2019 UK Government study using tracking data from Hen Harriers in northern England and southern Scotland also found illegal killing to be the main factor limiting the recovery of the UK Hen Harrier population.
Scotland is the species’ UK stronghold with about 70-80% of the UK breeding population of Hen Harriers here, mostly found in Orkney and the Hebrides. However, the estimated 460 breeding pairs by the 2016 national survey is just a third of the estimated population size of 1500 breeding pairs that habitat in Scotland could support, according to the 2011 UK Government report.
For the new study researchers used satellite tracking devices to look into the survival and movements of Hen Harriers. Whilst these tags provide critical insights into the ecology of the species and aid in conservation, they can also be used to recover dead Hen Harriers, thus allowing the cause of death to be identified.
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, of which 86 were in Scotland, funded by the Hen Harrier LIFE project. The scientists analysed the data and 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 (males: 14%; females: 30%), with illegal killing accounting for the deaths of 27-41% of birds under one year, and 75% of mortality in birds aged between one and two years. Not enough birds survived over two years to estimate mortality due to illegal killing of adults.
The authors found multiple strands of compelling evidence that illegal killing is associated with land management for grouse shooting. A 10% increase in grouse moor use by the birds was associated with a 43% increase in the rate of mortality. There was also a strong overlap between the extent of mortality in 20km squares and the area of grouse moor, with hotspots of illegal killing identified in the central and eastern highlands of Scotland and northern England. In contrast, there were no clear associations between use of grouse moors and death due to natural causes.
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.”
Duncan Orr-Ewing, Head of Species and Land Management. RSPB Scotland, said: “This study reinforces the devastating impact that illegal killing is having on our Hen Harrier population, how strongly it is associated with grouse moors, and why urgent changes are needed to bring this to an end. There should be three times as many breeding pairs of Hen Harriers in Scotland than we currently have.”
“Thankfully the Scottish Government has undertaken an independent review of the evidence and is now taking action. It is proposing to licence grouse shooting with sanctions including the removal of the right to shoot grouse where wildlife crimes are confirmed, and to provide a meaningful deterrent to wildlife crime. We hope to give evidence to the Rural Affairs and Islands Committee of the Scottish Parliament when it considers the draft Wildlife Management and Muirburn Bill shortly and to present the details of this study. The illegal killing of Hen Harriers, and other birds of prey, has no place in the nature and climate emergency and must end.
“One example of many incidents recorded as part of this study is Rannoch, a young female Hen Harrier, who fledged from a Perthshire nest in July 2017. Her remains were recovered in May 2019 on a Perthshire grouse moor – she had been caught in an illegally set spring trap, and died an agonising death. We cannot have more of our precious Hen Harriers being killed in such a way. This study is a crucial piece of evidence in helping to secure them a better future.”