It answer depends upon how late?
If a pigeon comes home a few hours late say 5/6 hours on the wing the answer is very little a pigeon young or old when fit should not be bothered unduly by flying 6 hours.
So let them rest give them the usual recovery food and drink, check to see if the reason for them being late is obvious e.g. illness of do treat the cause. if the reason is not obvious and you suspect the pigeon just made a mistake, got caught up with a flock or was simply off course through inexperience or a hawk scare. These otherwise healthy pigeon you let them fly around the loft for the next few days and when fully recovered put them back into the training routine. Every pigeon is entitled to a mistake and should learn from the experience.
If the pigeon arrives the next day or several days later, then you should isolate the bird in a quarantine section, supply the usual recovery food and drink and observe for a few days to assess if the bird should be treated as a precaution so as not to infect your other birds when the bird is reintroduced to the loft.
If the pigeon arrives the next morning I generally do not automatically treat the unless I think it is ill any longer from the loft I automatically treat the bird with a 3 in 1 medicine. I like to return my pigeons back to the loft within the week and restart the training as soon as they are healthy. I make a note in my black book of all late arrivals to help me evaluate my pigeons at the end of the season generally one or two mistakes can often be ignored three or more would be a bad sign wherther the cause is mistakes, lack of fitness or illness.
Racing Pigeon Thoughts – What to do with Strays
I take a leave from Poultry Owners, they are obsessed with biological isolation and will make you walk through a disinfectant trough, don a sterile coat etc before they let you on their premises. I see no reason why pigeon flyers should not adapt the same regime we have a lot at stake I would even include a hand wash if you are going to handle the birds.
I will return to strays, firstly isolate the stray away from your birds, provide a recovery food and drink. The next morning release the bird on its own before you let your birds out ( I some times after dark leave the quarantine section open so the Stray can exit as soon as they wish)
If the bird heads for home that is job done, if the bird returns take it miles form your loft, then when you are doing your very next training session or travelling any where more than 5 miles from home and release it in isolation on the way to or when returning from the journey.
If the pigeon returns to your loft, keep the pigeon in isolation and report it to the authorities or owner. In these days of relative expensive courier services the owner will sometimes offer you ownership of the bird, I personally politely refuse obviously if the pigeon was mine it would have an entry in my black book and also strays have no place no matter how bred or how handsome they look in my plans.