An individual goes through 3 sets of feathers during first year of life. First is chick feathering and replacement of it starts as chick fuzz on head an neck replaced by contour / body feathers. Second is juvenile and replacement of it occurs as sexual maturity reached. Third set is usually complete by time frame / bones to near full size. In my games the third (first adult) feather set complete by age of 7 to 8 months after hatching. Thereafter a complete change over occurs annually in fall so as stated in previous posts, one molt per year.
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Some breeds differ and stress can effect pattern / frequency of feather loss and replacement. My California greys seem to have single major annual molt as indicated above but also seem to have a more or less continous turnover of flight feathers. I do not think that is normal. Birds stressed by heavy laying, high temperatures, parasites or predator yanking feathers out can replace some feathers some of time.