fitness and health and better feather cover non darkness birds usually start signes of falling to bits round about 3rd race (around neck and chest) but your darkness birds have already gone through this stage
darken your loft enough so the birds can get to have a drink the system will take the birds through the body moult but will leave the flight feathers intact well up to the longer races
a club member has a pigeon picked up by a non fancier its well flown down he carnt get a courier for at least 3 days member of public dosnt know what to do with him ?