A couple of weeks ago we blogged about the ‘disappearance’ of eight young satellite-tagged golden eagles on grouse moors in the Monadhliath Mountains of Highland Scotland (see here).
Keen to deflect attention away from the most likely suspects, the grouse-shooting industry claimed that windfarms were probably to blame – a claim that was easily debunked when it became apparent those windfarms didn’t actually exist (see here). Still, it made a change from them suggesting that trees are the biggest threat to golden eagles in Scotland (see here).
Now they’ve come up with another excuse but once again, it’s poorly researched and relies upon their assumption that nobody will bother checking their claimed ‘facts’.
Have a read of this press statement from the Scottish Countryside Alliance (SCA). Hilariously, the SCA suggests that ‘finger pointing at the shooting community, based on no evidence, must be resisted‘.
No evidence? Good grief. Try this, this, this, this, and, particularly pertinent to the Monadhliaths, try this (where a young gamekeeper on Moy Estate was found to have a jar containing four eagle leg rings that had previously been attached to young golden eagles)!
However, that’s not what this blog is about. What particularly interested us about this SCA statement was the following:
“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%“.
Gosh! A failure rate of 49% does seem high! That MUST be the most plausible explanation for the ‘disappearance’ of these eight golden eagles (and all the other satellite-tagged raptors that have ‘disappeared’ over grouse moors during the last ten years), right? These tags are failing left, right and centre and it’s nothing more sinister than that, right?
Naturally, we wanted to read these recently published research papers but tellingly, the SCA hadn’t provided any references. After a bit of digging, it becomes apparent why they were so reluctant to reveal their source. Fortunately (for us), those scientific heavyweights at Countryman’s Weekly helped us out and pointed us to this:
As the paper’s title suggests, this is a review of wildlife radio telemetry studies that have been undertaken in India between 1983-2013.
It’s an interesting paper (if you’re planning to use telemetry to study animal taxa in India) but what relevance it has to satellite-tag reliability on golden eagles in Highland Scotland is a bit of a mystery to us, especially when you realise that many of the studies refer to radio-tagging (as opposed to satellite-tagging) of mammals (including Asiatic elephants, Asiatic lions, tigers) and reptiles (gharials, turtles). Of 82 studies reviewed, only 14 involve birds.
If you look at Table 8 (showing the known cause of tag failures), of 72 (radio & satellite) tags (across all taxa) where ‘contact was lost’ or there was an ‘unknown failure’, the vast majority (68) appear to relate to tags that had been attached to Olive Ridley Turtles. If you then have a look at this paper (‘Why do Argos satellite tags deployed on marine animals stop transmitting?‘), you’ll see that the failure of the salt-water switch is an on-going issue. Quite how this issue can be the cause of ‘failing’ satellite tags on golden eagles in the Monadhliaths is beyond our comprehension. Perhaps the Scottish Government’s planned review of golden eagle satellite data will shed some light. But perhaps not.