Crop milk is a secretion from the lining of the crop of parent birds in some species that is regurgitated to young birds. It is found among all pigeons and doves, where it is also referred to as pigeon milk. Crop milk is also secreted from the crop of flamingos and male emperor penguins, suggesting independent evolution of this trait. Unlike in mammals where typically only females produce milk, crop milk is produced by both males and females in pigeons and flamingos; and in penguins, only by the male.