Manx-tagged Hen Harriers perish

RSPB Scotland has announced that it has lost two of this year’s satellite-tagged juvenile Hen Harriers from the Isle of Man.

The siblings, Mannin and his sister Grayse, were tagged on the Isle of Man on 3 July 2017 by members of the Scottish Raptor Study Group and Manx Ringing Group in partnership with Manx Birdlife. After fledging in July, Mannin explored his native island until 14 August, when the tag data showed he had left the island and headed north towards the Galloway coast in south-west Scotland. Unfortunately, he never completed the journey, with tag data showing that he had gone down in the sea, approximately 5 km off the Scottish coast.

This is the first time the RSPB has lost a tagged harrier at sea. Initially unsure whether the tag would continue to function, the answer came on 24 August. Having continued transmitting, the data showed Mannin’s body had reached the shore. A brief search of the area, near Kirkcudbright, revealed the harrier’s remains and the tag. As with all recovered birds, his body was submitted for examination. The post mortem report concluded that there was no evidence of trauma or health problems and that Mannin had recently eaten a small mammal.

What caused Mannin to go down in the sea remains a mystery – one possibility is being caught in heavy rain. Mannin’s sister, Grayse, has also died, with her body recovered on 9 August. The remains were examined by ZSL, whose interim diagnosis did not implicate human interference as a cause of death.

Neil Morris from Manx Birdlife said “Obviously, everyone involved in the project here in the Isle of Man is desperately sad that Grayse and Mannin have perished. Their early demise highlights the vulnerability of young birds learning to fend for themselves once they have fledged the nest. It also underlines the need for a large healthy population that can withstand such losses.

“At the same time, it’s wonderful to see Aalin coming through her first year so well, and to get such an insight to her behaviour. We need to know so much more about these wonderful birds of prey in order to formulate ever better conservation strategies. We shall continue the work to study Hen Harriers on the Isle of Man.”

While the deaths of both of these birds through natural causes is disappointing, the finding and recovery of their bodies and the tags was straightforward. As is to be expected, the transmitters continued to provide the RSPB with good location data, even after one of them had spent 10 days in the sea.

This is, however, in marked contrast to the disappearance of Calluna, whose perfectly functioning tag’s transmissions ended very abruptly on 12 August. Her last recorded position was on a grouse moor, a few miles north of Ballater, in the Cairngorms National Park, and her disappearance can is regarded as highly suspicious.

• Find out more about the RSPB's work with Hen Harriers on the Skydancer blog.