Last spring, a satellite-tagged hen harrier called ‘Highlander’ joined the ranks of the ‘missing’ as her sat tag suddenly stopped transmitting over a grouse moor in Co Durham (see here).
When you consider the extraordinarily high disappearance rate of young, tagged hen harriers (78.7% as of 2014) and the absence of breeding hen harriers on almost every driven grouse moor in the country, it wasn’t unreasonable to conclude that she’d been illegally killed.
But in Highlander’s case, she just may be the one who got away and against all the odds, survived past her second birthday. According to the RSPB’s Skydancer blog (see here), Highlander may still be alive and the cause of her ‘disappearance’ is likely to have been a satellite tag technical failure.
Predictably, the usual suspects from within the grouse shooting industry have already taken to social media to use today’s news as an opportunity to pretend that hen harriers are not routinely killed on grouse moors but that the many hen harriers that have been reported as ‘missing’ over the last ten years have suffered from satellite tag technical faults. That may be plausible for one or two ‘missing’ birds, but unfortunately for the grouse shooting propagandists, these technical failures don’t happen very often, and nor do sat tag technical failures explain the absence of breeding hen harriers on most driven grouse moors.
We know from a study of Montagu’s harriers, fitted with exactly the same type of tag as the UK hen harriers, that technical failures amount to just 6% (n = 67 tagged birds). Highlander’s failed tag is the first technical failure the RSPB has recorded (n = 23 tagged birds) so this failure rate is well within the expected range.
Satellite tag failure rates will be further scrutinised in the forthcoming review of satellite tag data from hen harriers, golden eagles and red kites in Scotland, which is expected to be completed by March. We know the grouse shooting industry is extremely twitchy about this review because they know as well as we do what the results are likely to show, and it won’t be good news for them. So it’s unsurprising that they’ll use every opportunity presented in the run up to that report being published to discredit the data, discredit the researchers who fit the tags, and discredit the tag-fitting techniques. Interestingly, you don’t see them trying to discredit the data, researchers or techniques associated with the satellite-tracking of woodcock (GWCT) or cuckoos (BTO) – it’s only the upland raptors. Funny that.
Photograph of Highlander (right) and her sister Sky being satellite tagged at their nest in Bowland in 2014 (photo by Mick Demain).