like many things theres a happy medium ,, it is my beleive if you have closed in lofts ,heaters lights etc , no good ,,,,pigeons will adapt to humidity levels [if they have the constitution] if pigeons can get a fly each day , using their respiratory system ,lungs, heart etc etc this , along with decent ventilation ,and a clean loft [2 inches of droppings under the perches would provide too much humidity and stale air ,and dampness] ,, proper amount of pigeons per air space is a must [half to one cubic meter per bird depending on ventilation , is quite suffice,, pigeons up north start racing later than pigeons down south [and still to early ] it would be easy to" false" condition a bird to win a 60 mile race in the begginning of april by false means ,,,but how long would this condition last ? if your black minerals are dry in a galley pot at the back of the loft ,,your spot on ,, were now guilty of breeding softies