The disappearance of Hen Harrier ‘Highlander’ off the airwaves may be due to tag failure, though this isn’t yet certain, but a tagged adult female answering to the description of Highlander (brown with a white rump but with an aerial that kinks left) has been spotted in some of her earlier haunts.
I was interested to read this on the RSPB Skydancer blog:
Satellite tags of this type are designed to last for up to 5 years (though sadly, hen harriers rarely seem to live that long). Highlander’s tag was two years old and is the only confirmed failure out of 23 RSPB-monitored hen harrier satellite tags deployed in the last 3 years (ie a 4% failure rate). Researchers at the Dutch Montagu’s Harrier Foundation have previously recorded a 6% technical failure rate (out of 67 birds tagged) using exactly the same make and model of satellite tag, with all failures occurring on tags older than at least one year. This puts the failure of this bird’s tag well within the realms of expected normality, so I suppose we shouldn’t be surprised that something like this would happen sooner or later.