I rescued a female house sparrow a few months ago as a hatchling and she never grew as big as other sparrows, and has never had a coat that lacked breakage or dinginess. She is very spry and seems healthy as can be. I've took her to bird "experts" numerous times and they always say she's healthy and probably just molting, but she is around four months old and has always had broken, dirty-looking feathers (regardless of bathing). what could be happening?