Could someone explain to me about the leg bands? What is on the leg band? Do I put what I want on the leg band or is it like a registration that I will be given a number? Can I pick my own color? Then I thought you put the band on the pigeon and it stayed on them for ever but I just saw bands in differrent sizes. Do you change the bands as they get bigger? Also could someone tell me where to get the bands? Thanks for your help.