I wasn't disappointed when I noticed a bird with a yellow ring, with the code 250B. I knew from a sighting I had of one of their birds last winter (see here), that this was a bird from a project in Mayo, run by Eoin McGreal and Chris Benson.
My sighting is the first in 3 years, and the fact I recorded the bird so soon after the breeding season, would suggest that it either failed to breed at Lough Mask this year and has returned to the wintering grounds already, or that it is breeding at a colony much nearer, possibly on Lough Neagh.
The same bird was still at Sprucefield yesterday, as was one of my birds, 2ACS.
Many thanks to Eoin for the information.