We were all thrilled when we were able to confirm that one of our original satellite tagged white-tailed eagle chicks Mara had settled to establish a territory of his own. It was even more exciting when we also confirmed that he had paired up with a female from the east coast project 'somewhere on the Scottish mainland'. You may have seen him on BBC Springwatch in June after cameraman Mark Yates managed to capture some lovely images of him and his mate. Presenter Iolo Williams explained to Michaela Strachan how they were making a nesting attempt and were incubating a clutch of eggs. Subsequently, we weren't surprised that the eggs failed to hatch as both birds were still only 4 years old but the signs were very hopeful for the future.

We stopped plotting Mara's whereabouts on the tracking map in order to protect his specific location and nesting attempt but he has really done his bit for white-tailed eagle science. Since the day we fitted his tag (along with his sister Breagha) we have been able to follow his every move and for the first time ever we have a complete picture of how young white-tailed eagles disperse: where they go, how long they stay in certain areas and use certain habitats and when they decide to start settling down. Gordon Buchanan who filmed the fitting of the tag for BBC Autumnwatch in 2008 and Roy Dennis of The Highland Foundation for Wildlife who fitted it were equally delighted by both Mara's and the sat tag's performance. The data has all been carefully plotted over the years by the RSPB Web Team and stored by our colleagues in the RSPB Data Unit. We've also had help on this ground-breaking project from Natural Research Ltd, Scottish Natural Heritage, Forestry Commission Scotland, BBC Wildlife Fund and the Mull & Iona Community Trust - all of whom have either contributed towards the costs of the tags and tracking or have helped in other ways. Thank you all.

So, dear reader, imagine our worries and fears when in recent weeks we started getting data through that showed Mara's satellite signal was repeatedly coming from exactly the same location over several days. It wasn't just that Mara was roosting in the same tree or feeding in the same spot. This signal was also showing that there was no movement, no activity. This kind of news can often mean very bad news and in the past other satellite tagged eagles have been recovered dead as a result of illegal poisoning. RSPB Investigations staff and the police carried out a search and were able to go straight to the spot, such is the accuracy of the satellite signals. We all held our breaths but quietly we all feared the same result.

Then I got the call from the team. It wasn't a dead eagle! There was huge relief for everyone. It was just the satellite tag itself which had become detatched -  just as they are designed to do. The police and Roy Dennis who has fitted many tags are completely content that after 4-5 years the stitching on the join of the straps which held the tag in place had weathered and worn in exactly the right way allowing the straps to come off and the tag will have fallen safely to the ground. Mara will have had a good shake, a quick preen and will have flown on, possibly wondering where his amazing piece of light-weight technology which has been with him almost all his life, had gone. But I doubt he'll miss it! The old satellite tag which can cost up to £3000 will be sent away to be repaired and checked over and may one day help us to reveal new secrets somewhere else. Whilst  we haven't been able to see Mara recently we are confident he has come to no harm. As his mate is a 2008 east coast release and if her radio is still working we will be able to track her and hopefully find Mara not far away. Their territory is remote and vast so there may not be news for a while but we will keep you posted on any future developments or sightings. Mara has contributed hugely to the world of white-tailed eagle science. Skye and Frisa can be justly proud of what their son has achieved!

Meanwhile, we've also just heard that Shelly's satellite tag has also been recovered from a lonely moor in the Western Isles where she has been spending alot of time over recent months. This tag too looks like it simply became detatched and that she has not come to any harm. This tag has come off  somewhat sooner than we would have expected but it has been known before and the tough cotton thread can weather at different rates. Shelly is the female chick of Fingal and Iona at the Glen Seilisdeir Mull Eagle Hide from 2010.

And then there was one! Young Midge from 2010 now flies the flag for all Mull satellite tagged white-tailed eagles. The project has shown us so much about immature eagle dispersal and has filled in many of the gaps in our knowledge that wing tags just couldn't tell us. We wish Midge well for the future and will keep the tracking map updated as and when so you can follow his fortunes. Long live the Midge!

Dave Sexton RSPB Scotland Mull Officer