Satellite-tagged hen harriers regularly ‘disappear’ in the UK uplands, mostly in areas managed as driven grouse moors. Indeed, according to data from Natural England, of 47 hen harriers that were satellite-tagged between 2007-2014, a staggering 78.7% were listed as ‘missing’ (see here). That means a significant and suspiciously high proportion (37 tagged hen harriers) vanished without trace.
And of course it’s not just hen harriers. Last month we learned that eight satellite-tagged golden eagles had ‘disappeared’ on grouse moors in the Monadhliath mountains (see here).
Various unsubstantiated ‘explanations’ for these ‘disappearances’ are routinely trotted out by the persecution apologists, including claims that ‘bird activists’ are killing the birds to smear the grouse shooting industry (here) or that the birds have been killed at windfarms and their bodies removed to avert bad publicity….quite plausible until we discovered that the majority of the windfarms blamed for the disappearance of eight golden eagles hadn’t actually been built (see here).
And then we get the old familiar excuse that it must have been a technical failure with the satellite tag. Again, quite plausible if it happened every so often, but not if it’s happening with the frequency with which the grouse-shooting industry claims. Last month, the credibility of this excuse was blown apart when the Scottish Countryside Alliance published the following statement in response to the news about the eight ‘missing’ sat tagged golden eagles:
“Contrary to claims that transmitters are reliable, research papers published in 2013 studied three decades of wildlife radio telemetry and concluded that failure rates could be as high as 49%“.
It turned out that the SCA was disingenuously using data from satellite-tagged Olive Ridley turtles in India where problems with a saltwater switch on the tag is a known and on-going issue and so the SCA’s claim of a 49% failure rate was actually based on a totally irrelevant study and as such was highly misleading (see here). You can make up your own minds about whether this was a case of the SCA’s inability to interpret simple scientific data or whether it was deliberate propaganda pushed out to divert attention from illegal killing in the hope that nobody would check the details.
Wouldn’t it be great if, instead of relying on misrepresentative data from marine turtles in the Indian Ocean, there was a relatively comparative study of satellite tag reliability on, say, a harrier species in western Europe.
Oh, hang on, there is!
Have a look at this blog that has just been published on the RSPB’s website. It’s written by Dr Raymond Klaassen of the Dutch Montagu’s Harrier Foundation. Raymond and his colleagues have been satellite-tagging Montagu’s harriers (67 of them since 2006), using the same make and model as the sat tags being fitted to hen harriers in the UK.
So what does Raymond say about satellite tag reliability in his study? Amongst other things, he says this:
“Technical failures generally are rare. We have recorded a few throughout the years (6% of all cases), however failures have always been preceded by irregular transmission periods and, most importantly, a drop in battery voltage (another parameter monitored by the transmitter). This makes it relatively straightforward to distinguish between a likely mortality event and a likely transmitter failure“.
Wow. A six per cent technical failure rate over a ten year period. It turns out that these harrier satellite tags are actually highly reliable. Who knew? Compare that six per cent failure rate with the 78.7% rate of ‘disappearing’ hen harriers over a seven year period, supposedly the victims of satellite tag ‘technical failures’.
We trust this compelling evidence of satellite tag reliability will be included in the Scottish Government’s review of satellite tag data from three raptor species that routinely ‘disappear’ on grouse moors across Scotland (see here).
Photo of Raymond with a satellite-tagged Montagu’s harrier by Mark Thomas.