From a story I read today here on Wildlifeextra.com, bird ringing is 100years old and over 36 million birds ringed.
Now clearly they can be a pain to us photographers as they show the 'hand of man' on our wild subjects. It is particularly galling when it is a rarish or difficult to capture subject.
But it is clearly vital to monitor our valuable wildlife and the research has been critical for understanding behaviours, movements and lifespans.
Martin