Largest ever satellite-tracking study shows illegal killing major cause of death in Hen Harriers
As new research finds that illegal killing accounts for up to 75% of annual mortality in some age classes of Hen Harriers, and that mortality due to illegal killing was higher in areas managed for Red Grouse shooting, the urgent need for legislative reform and licensing of gamebird management has never been more stark.
The Hen Harrier is a ground-nesting bird of open moorland. Despite receiving the highest level of legal protection, Hen Harriers are a Red Listed bird and numbers have declined across the UK. Hen Harriers prey on a variety of small mammals and birds, however, its ability to prey on Red Grouse has led to it being the target of illegal killing by some who wish to protect populations of this gamebird for recreational shooting.
Scientifically proven, legal solutions are available which can reduce grouse predation to negligible levels. For example, diversionary feeding is where substitute food is placed near the nest under licence, reducing the need for adult birds to hunt. However, voluntary resolution of this conflict has so far failed to prevent illegal killings.
In 2019, a study of Hen Harriers satellite-tagged by Natural England revealed that 72% of the 58 birds tracked were either confirmed or considered very likely to have been illegally killed (Murgatroyd et al, 2019). It also found that only 17% of satellite-tracked Hen Harriers survived their first year, and the probability of them dying increased the longer they spent on grouse moors and peaked in protected areas comprising proportionately more area managed for grouse shooting.
The latest study led by the RSPB
Now, in the largest ever study of its kind, a new paper by Ewing et al, adds fresh weight to these concerning statistics through analysis of the movement and fates of 148 Hen Harriers, satellite-tagged in nests across England, Scotland, Wales, and the Isle of Man, between 2014 and 2021.
Mirroring the methods used by Murgatroyd et al, researchers determined that 43 of the tracked birds were likely to have been illegally killed, as they had disappeared after their tags exhibited a sudden stop in transmission, despite no apparent malfunction. Rigorous efforts were made to relocate each of these individuals, but to no avail. Independent post-mortem examinations also noted six instances of confirmed persecution, including three killed with shotguns; one caught in a spring trap; one poisoned; and one where a recovered harness had been cleared tampered with. One further Hen Harrier, which died of natural causes, was found to have fragments of shot gun pellets in its leg from a previously persecution attempt.
While natural mortality was high, illegal killing nevertheless accounted for 27-41% of deaths in first year birds and 75% in harriers between one and two years. Only a single male (out of 65 tagged) survived past two years of age and illegal killing (28.6%) contributed more to overall mortality of adult females than natural mortality (14.3%). Researchers found that just 14% of male Hen Harriers and 30% of females survived their first year and that the median lifespan of harriers after fledging was just 121 days.
For those who may wonder about the role that technology failure might play in studies like these, satellite tags were shown, once again, to be an exceptionally reliable technology with technical failure of tags recorded in only 4 instances (< 3%) in this study.
Female Hen Harrier in flight (Credit: Mark Thomas (RSPB Images))
The results of the study.
To explore things further, Ewing et al looked at the timing and geographical spread of Hen Harrier deaths from both natural causes and illegal killing, to see if any patterns emerged. The analysis provides convincing evidence between illegal killing and grouse moor management:
Something needs to change.
Adult Female Hen Harrier perched on heather (Image Credit: Andy Hay (RSPB Images))
Under the Government-led Joint Hen Harrier Action Plan, attempts to tackle persecution have included trialling a controversial system of Brood Management, to which the RSPB remains strongly opposed on scientific and ethical grounds. Brood Management involves removing Hen Harrier eggs or chicks from nests on driven grouse moors, if there are two nests within 10km of each other, at the landowner’s request, to be reared in captivity and later released.
The intention is to change attitudes of grouse moor managers towards Hen Harriers, through reducing local predation pressure on Red Grouse and thus reducing levels of illegal persecution. An initial review by Natural England of the first-year survival rates of the 20 tagged and released Brood Managed birds up to 2021, compared to Natural England tagged wild-reared birds over the same period, suggests whilst that Brood Managed birds had markedly improved first year survival; this had not transferred to wild-reared birds as was predicted in the trial framework. Natural England state that further analysis is needed, to assess the outcomes and any corresponding change in social attitudes towards Hen Harriers, and have extended the trial for further two years.
Hen Harrier numbers in England have increased steadily over the last few years, and that is to be welcomed, however success of the coming season is yet to be seen and numbers remain far below what the available habitat could support. Crucially, there has so far been no evidence of a corresponding drop in illegal killing.
Since the conclusion of the new study, which follows Hen Harrier survival through to the end of May 2021, a total of 34 harriers have either been confirmed as illegally killed or have “disappeared” in suspicious circumstances, in England – including 21 in just the last 12 months. Others include a female Hen Harrier whose tag was later found by police forensics to have been deliberately cut off, after she roosted on a grouse moor in the Peak District, and another whose tag and harness were discovered attached to a live crow, indicating the harrier’s wings had been cut off to remove the harness – both instances, clear evidence of deliberate attempts to cover up illegal killing. More shocking still, four young hen harrier chicks were found stamped to death in their nest, on a grouse moor, in the Yorkshire Dales, in June 2022.
The National Hen Harrier Survey underway this year will give us a true picture of how the breeding Hen Harriers population across the UK is faring. However, despite recent increases, it is clear that illegal killing continues to actively suppress the population and numbers remain far below the carrying capacity of the English uplands.
The results of this new study, along with those of Murgatroyd et al (2019) demonstrate that continued illegal killing is the main factor holding back the recovery of this bird of prey.
In December 2022, five short months ago, the UK Government stood shoulder-to-shoulder with global leaders on the international stage, in being an enthusiastic signatory to the Kunming-Montreal Global Biodiversity Framework (GBF). Target 4 of that Framework committed signatories to:
“Ensure urgent management actions to halt human induced extinction of known threatened species and for the recovery and conservation of species, in particular threatened species, to significantly reduce extinction risk.”
Shortly after the GBF was agreed, DEFRA published the Environmental Improvement Plan (EIP) – a review of the 25 Year Environment Plan, which states “The target to halt the decline of species by 2030 is our apex target.” If either of these domestic or international targets is to be achieved, the illegal persecution of Hen Harriers must be stopped.
The devolved Scottish Government have recently published a bill, proposing to introduce a licensing scheme for grouse moors. If passed, this much-anticipated piece of legislation would give Nature Scot (the Scottish equivalent of Natural England) the power to revoke individual grouse moor licences from estates where criminal activity related to raptor persecution is detected.
The RSPB is now, once again, calling on Westminster Government to introduce a similar system of grouse moor licensing for England. Voluntary measures have failed. There is no evidence to suggest that brood management is working. An effective system of licensing would allow those who operate within the law to continue doing so, unimpeded, while finally providing appropriately strong penalties to have an effective and meaningful deterrent to criminal behaviour.
The evidence is stark and now, thanks to this new paper, it is there for all to see. It is past time for change.
The killing has to stop.