Four birds w/ one stone ... might be settin' a BYC record ~'-)
Give your birds an astringent solution at the rate of four teaspoons of Apple Cider Vinegar to each gallon of water (but never in galvanized metal containers). The tannin in ACV will reduce the viscosity of mucus, and 'cuts through' the coatings in the mouth, throat and intestines, improving the uptake of nutrients/vitamins, and is useful in the treatment of any respiratory disease, as it helps them to expel the mucus from their system. It also reduces the presence of botulism, and is the only effective treatment for the toxin it produces. The target pH is 5~6, or slightly acidic, which also creates a hostile environment for internal parasites ... all that goodness, and for quite literally pennies per gallon ~;-)
It can (and probably should) be given continuously, and truly can't harm a single feather on your birds ...