The crop of both sexes of pigeons produces milk, called ‘pigeon’s milk’, during the breeding season. Internal epithelial lining of the crop is a little thickened in the form of two large patches. These are called crop glands but these are not glands. The milk is produced by the degeneration of the cells of the epithelial lining of the crop. The prolactin hormone, secreted by the pituitary gland, stimulates and controls the formation of milk. The milk is regurgitated into the mouth of the young ones by both the parents. This feeding continues till the young ones arc able to feed on grains. Pigeon’s milk is soft and cheesy and contains water, fat, protein (casein) and lactose. It contains 35% fat, compared to 3 to 5% in cow’s milk. It is more nourishing than the mammalian milk. Young ones, fed with it, double their hatching weight only in two days. A rabbit doubles its birth weight in six days, and a cat in nine days. Some parrots also produce milk.