We had an intruder osprey visitor yesterday - and we could ID him. Finally!

Since her valiant battles with Blue 24 in April, Glesni has defended her regained nest with stoicism and determination. She has kept a constant 24-hour vigil over everything around her - until yesterday.

Blue 80

As Glesni is more or less fishing for herself now and is about to start her southerly migration any day, she let her guard down, just for a few minutes, and for just enough time for this handsome chap to sneak in and have a four-minute dialogue with Deri. Or maybe 'monologue' would be more descriptive.

Deri greets the new stranger with open wings. Not.

Blue 80 is a 2012 bird, hatched on 11th May in the Glaslyn nest. He hatched after 38 days, fledged at 54 days old and weighed 1,420g at the time he was five weeks old (Ceulan weighed 1,415g that year - almost identical). This is the first time that Blue 80 has been identified as having returned to the UK as an adult and as being very much alive!

Glaslyn brood of three in 2012

Osprey chicks usually take at least two years to return to the UK as adults from migration. So up to 2012, 21 young ospreys had fledged the Glaslyn nest and with the positive Blue 80 sighting yesterday, six of those 21 have been now been identified as having returned - that's almost 30%.

Of course, there could be more out there, especially from 2011 and 2012 (six in all, two broods of three) as these birds wouldn't have had the time to be spotted yet.

Something else struck me last night. We've had male intruders at the Dyfi for a few weeks now, but none of these intruders have had the opportunity to land and be identified (thanks Glesni!). What if these male intruders were not different birds, but the same one. What if they were all Blue 80?

Have a look at this collage of images taken over a six week period of the male intruder. He seems to be missing (moulting) a primary feather on the right wing, four in from the leading edge (so P7 probably). It looks like P7 is missing from the left wing also - many birds moult feathers like this in corresponding couples, including ospreys.

Blue 80 may have been around since at least July 5th!

We have to be careful though. Wouldn't this P7 feather have grown back in six weeks?

The best identifier of ospreys (apart from rings, obviously) is underwing patterning. Head markings and chest plumage are also useful but very difficult to assess usually from photographs of far away birds.

Here's Blue 80's underwing pattern taken from the video above:

He has a very pale underwing (just like his Dad) and individual 'cobbles' of brown. These are his own personal signature - an underwing fingerprint. If he is photographed again in flight - this photo could prove to be a great tool in identifying him as Blue 80. Rings are often hidden or partially obscured when ospreys are in flight.

Here's a photo of Blue 80's father with his very pale underbelly and wings

What magnificent news for all those up at Glaslyn. All the planning, the managing, the coordinating and the protecting of Blue 80 as an egg and chick - 24 hours a day. This is payback time - this is the light at the end of the tunnel. The reward.

The Glaslyn Osprey Project is now managed by volunteers after the RSPB pulled out in 2013. The group is called Bywyd Gwyllt Glaslyn Wildlife - Glaslyn Ospreys. You can view their website here and their Facebook page here. Please support them.

Finally, a big 'thank-you' to all the thousands of volunteers that ring ospreys and most other bird species in the UK every year. For over a century now the information from these ringed birds has helped us get a better understanding of bird ecology and migration.

Where birds migrate to, how long they live, amount of inbreeding tolerance, natal dispersion, levels of osprey immigration and emigration, causes of death, and a lot more stuff. This information helps conservationists set out plans for ospreys in the UK. Indeed, if it wasn't for bird ringing, Blue 80 would probably not be here at all.

His father was born in Scotland in 1998 and translocated to Rutland at a few weeks old. Why? Because the population expansion rate of ospreys is so slow - around 4Km per year, it could have taken centuries for the osprey to recolonise the UK naturally. Humans persecuted ospreys to extinction in the UK over hundreds of years - how ironic that humans are now helping them get a foothold again.

Bird ringing in the UK is coordinated by the BTO, British Trust for Ornithology.

Many congratulations to the folks at the Glaslyn - Llongyfarchaidau mawr i chi. We'll be keeping our Dyfi nest cameras turned on for a few weeks yet - you just never know who might land next. After all, Blue 80 did have a brother and sister in 2012.

Keep Calm and Look Up!