An interesting observation; in the vast majority of birds the right ovary starts to degenerate in the first month or so. The main reason birds do lay eggs is so that they don't have to fly with a heavy load [some completed egg clutches weigh more than the actual bird laying them]. To save further on unneeded weight the right ovary shrinks to an nonfunctional vestigial flap. Even the functioning ovary and in the cocks the testes shrink somewhat out of breeding season, rapidly regrowing to a functional size when conditions are right for breeding.