This video shows the release of tens of thousands of racing pigeons at the start of their journey back to their home lofts. It's quite a sight.
I've seen this in the flesh a couple of times. It's advisable to bring an umbrella . . . the pigeons frequently 'let go' as soon as they're out of their transport cages, and the resulting rain of ordure can be both smelly and damaging to your clothes!
(How do I know this, you ask? Trust me. I know this!)