Of course, in years gone by the recovery of dead birds with tags or rings was an important element in transforming the hobby of birdwatching into the science of ornithology. Recoveries and 'controls' provided evidence of how long various species lived and the routes and destinations of their migrations. Of more interest, I suspect, to many modern birders is the fact that reading a bird's ring details can prove beyond doubt that the Wood Duck you just added to your list really did fly across the Atlantic and not merely hop the wire from Pensthorpe.
But do we really need to carry on ringing everyday species such as Robins and Blackbirds? The daily reports of the better-known 'ringing stations' seem mostly to consist of these and other familiar species. Surely we're not learning anything new by adding a third or fourth ring to those already present on the leg of a Song Thrush? It does sometimes seem as if it's the ringing itself that is the object: 'Today our ringing totals were 4 Wrens, 6 Robins, 6 Dunnocks and 3 Blackbirds' It all seems a bit close to bus or train spotting!
I recall that much of Sir Peter Scott's study of Swan migration was based on his careful observation of the bill-patterns of Bewick's and Whoopers: surely the same skills could be applied to birds such as Marsh Harriers that often display distinctive plumage?
I find it very hard to believe that half a dozen rings on the legs of a wading bird don't have some effect on its ability to feed or evade predators: with due respect to Beyoncé: 'If you liked it, then you shouldn't put a ring on it'