A post-mortem of the mutilated bird concluded that its head and leg wearing a metal ring for identification had been pulled off while still alive, consistent with illegal persecution.
Twenty more hen harriers, including 15 that were part of satellite-tagged tracking projects, have also disappeared across Northern England in 12 months, with seven birds lost in the same area in the Yorkshire Dales.
The raptor is on the red list of birds of conservation concern in the UK, with just 545 pairs recorded in 2016, a decline of 13% since 2010. In England there were 34 successful nests in 2022, despite enough habitat and food to support over 300 pairs.
In 2019, a study by the government found illegal killing to be the main factor limiting the recovery of the hen harrier population.
Seven of the birds, including the one that had been mutilated, were from the same area in Birkdale, an area of driven grouse moor in the Yorkshire Dales National Park on the North Yorkshire/Cumbria border.
The police carried out a search warrant in connection with the incidents, but the ensuing investigation has failed to lead to charges.
During the autumn of 2022, two further RSPB-tagged birds vanished in Cumbria and Durham, both also on grouse moors.
These nine birds are separate to another seven Natural England satellite-tagged hen harriers recorded as missing, over the past year.
Finally, also in the past year, five (un-tagged) breeding male hen harriers have vanished, including two in the Peak District National Park in 2022 and, in April this year, one in Durham and two from the RSPB’s Geltsdale Nature Reserve in Cumbria: both these birds had active nests which have now been abandoned, one containing three cold eggs.
Male harriers are known to hunt away from their nest sites, and this is not the first time that adult male harriers with active nests have vanished from Geltsdale in recent years, the RSPB said.
All 21 birds were reported at the time by the RSPB and Natural England to the police and the National Wildlife Crime Unit.
Commenting on the situation, the RSPB’s conservation director Katie-Jo Luxton said: “These 21 birds represent a significant proportion of the existing English hen harrier population. The government’s own study found illegal killing to be the main reason preventing the recovery of this species, and these recent events indicate that the situation has yet to improve for this rare and beautiful bird.”
Natural England strategy director John Holmes said: “We are sickened by this evidence of persecution, which remains a serious issue and needs more focus and action from the police, businesses, landowners, and game management interests.”
The organisation said it would continue to track down tags that stop transmitting, and to support the police in their role of bringing those responsible to justice.
A spokeswoman for North Yorkshire Police said that its rural task force was committed to putting a stop to the “inhumane and callous crime,” and bring the perpetrators to justice.
“The remote and isolated areas where these crimes usually take place presents challenges in itself when it comes to gathering sufficient evidence to prosecute.
“The frustration of wildlife agencies is shared by our dedicated wildlife crime officers who work hard to protect the many species that call North Yorkshire home,” she said.