And what, may I ask, do you deduce from the fact that on the day you counted them 0.5% of the Trafalgar Square pigeons carried some form of marker rings? Were they all English birds, or did any come from Wales, Scotland, Ireland, or even further afield, say Holland, Belgium or France? Maybe you don't know, after all why should you when to you a pigeon is a pigeon is a pigeon!
As I've already said, the day I counted them there were none. Therefore based on our respective counts it is possible to say that the number of ringed racing pigeons resident in Trafalgar Square can range from between 0 up to and including a maximum of 6.
Just because you haven't personally seen it doesn't mean it's impossible for someone else to have seen 10 pigeons brought to one eyrie in one day. In this instance, the figure was quoted by Dr Andrew Dixon who has extensively studied the predation of Racing Pigeons by Peregrine Falcons, particularly in South Wales. I'm sure the ever-present 'valley boy' will have heard of him and may even know him and have helped him in his work. Therefore, the '10 per day' figure was
NOT simply plucked out of the air by pigeon fanciers as you seem to imply, but rather arrived at by an acknowledged expert on Peregrine Falcons.
(Reference for any Doubting Thomas's - http://www.rpra.org/raptors.html paragraph headed 'Delaying the start of the old bird racing season.'
In future, LB, PLEASE try to do a bit of your own leg-work!