Both male and female pigeons produce a nutrient-rich 'milk' to feed their young.

Crop milk is a unique substance produced in the crop of pigeons, doves, flamingos, and male emperor penguins. In pigeons, the process is regulated by the hormone prolactin, which is the same hormone responsible for lactation in mammals. About two days before eggs hatch, the walls of the parents' crops begin to thicken and shed cells filled with high levels of lipids and proteins.This 'milk' is significantly more concentrated than mammalian milk. It consists of roughly 60% protein and 32% to 36% fat, while lacking the carbohydrates and calcium found in cow milk. Because it contains no lactose, it is highly digestible for the young squabs. Research published in the journal 'BMC Genomics' in 2011 highlighted that crop milk also contains antioxidants and immune-enhancing antibodies to protect the chicks.The evolutionary advantage of crop milk is immense. It allows pigeons to breed in various environments and seasons because the parents do not need to find specific high-protein insects to feed their young. Instead, they convert their own bodily reserves into a complete nutritional source. This efficiency is why a squab can grow at an incredible rate, often increasing its birth weight by 100% within the first two days of life.