Satellite tag reliability: compelling evidence from Montagu’s Harrier study

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.

17 thoughts on “Satellite tag reliability: compelling evidence from Montagu’s Harrier study”

  1. the next thing to do would be to interrogate the british tracking data to see if they demonstrate the same drop in voltage prior to failure.if this voltage drop is not there then this would demonstrate a different cause of the end of transmission possibly

  2. In my experience of following sat tagged ospreys, transmitters very rarely fail and usually if one stops working in a certain area the body and the transmitter can be found even in the sahara desert as with 09(98) from Rutland.

  3. Surely Natural England were slow/ reluctant to release the data on the 47 hen harriers? Seems they might also be slow in finding the same patterns of failure observed with the montagu study, or reluctant to declare what would be the same conclusive evidence of persecution!

  4. And of course Monty’s do not frequent Moorland habitat! If they did then the amount of sat tag failures would not surprisingly increase!

    1. Not strictly correct. A number of years ago I followed up a report of a pair of Hen Harriers displaying on heather moorland, only to find that they were Montys. They raised three young in a nest in rank heather.

  5. I think the probable reason for the high failure rate of Hen Harrier tags is caused by smoke infiltration from the many moorland fires they have to fly over at peak nesting time, another possible cause is disruption of the transmitter frequency when passing over the sonic boom of a moorland bird scaring device set close to or on Hen Harrier breeding territories.

    What could have been closely linked but has nothing to do with transmitters is the loss of Hen Harriers by predation from Goshawks, Peregrines and Golden Eagles, but seeing as they are now also missing from most if not all grouse moors they can’t be to blame. The almost total disappearance of birds of prey from these areas continues to be an enigma and they are fast becoming known as “Raptor Black Holes” along with the disappearing wind farms.

    All this adverse publicity can’t be doing the reputation of the Grouse shooting estates any good, most of which claim to work within the law and would never dream of harming protected birds of prey and wildlife, would they? Many of the grouse shooting estate owners are esteemed peers of the realm and pillars of society, they are rapidly losing face in the blaze of recent publicity painting them as countryside vandals, environment destroyers and wildlife persecutors, everyone knows these type of people would never stoop so low to be caught doing such things, I mean to say, how could they, they are above all that sort of thing. Their gamekeepers, those stalwart guardians of the countryside are being shown up to look like criminals, this could have consequences for their employers who may be “quite innocent” of any wrongdoing either accidental or intentional.

  6. The ongoing Hen Harrier dispute will soon be discussed on the BBC’s Landward programme.

    Given the BBC’s past bias in favour of the shooting industry, I won’t expect any change in their stance, and I’m quite sure that the true extent of raptor persecution will be downplayed considerably, with a host of other reasons given as an explanation as to why the species fares so badly on grouse moors.

    I hope i am proved wrong, so time will tell.

    1. Oh well, that was another piece of whitewashed BBC pish!

      If the BBC and SNH is to believed, the sole reasons for Hen Harrier fatalities are fluctuating temperature patterns and foxes, and that the only hope for the Hen Harrier is grouse moor management.

      FFS, when will these lying bastard organisations ever tell the truth?

      1. FFS indeed!
        It is a travesty of justice for our natural heritage.
        The BBC, and Conservatives for that matter, will never admit the truth when it comes to matters that are entwined within royalty or rich landowners of the grouse moor kind.
        It’s a modern day scandal that protected nature is quietly destroyed by employees of grouse moor owners; for ‘driven grouse moor gamekeepers’ read ‘protected wildlife killers’.
        In my mind, as long as the Cons are in charge then there is no chance of this situation being sorted for the good.

  7. So glad to read Prince William is getting behind the plight of the elephant as he fears it is fast becoming extinct.

    Wonder why he has not chosen to support protecting some species a bit closer to home that are facing a similar fate.

  8. I have just contacted the BBC radio 4 programme “More or Less” in which “Tim Harford explains – and sometimes debunks – the numbers and statistics used in political debate, the news and everyday life” to ask them to investigate the statistics behind satellite tagged birds of prey. It would make an interesting item and help raise the issue of “disappearing tagged birds” to a wider audience.
    Perhaps others might like to do the same with a link to this page.

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