A female bird is commonly referred to as a hen. All hens develop ovaries when it's breeding season. When breeding season is over, the ovaries become smaller.
The effectiveness of a hen's ovaries is determined by the life cycle of its species. Once the hen's ovaries start to develop, follicles begin to grow on the outer definable cortex of the ovaries. The medulla turns into a vascular zone that features nerves and blood vessels. Once an ovary is stimulated by hormones during the lay period, it bulges into the abdomen. The male counterpart of the hen is known as a rooster.