Pigeon milk, also known as crop milk, is a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation. Similar crop milk is also produced by flamingos. Crop milk bears little resemblance to mammals' milk, being a semi-solid substance somewhat like pale yellow cottage cheese. It is very high in protein and fat and, in fact, contains more of it than cow or human milk. Both male and female adult birds produce crop milk and share in the feeding and care of the young.
Pigeon's milk begins to be produced a couple of days before the eggs are due to hatch. The parents may cease to eat at this point in order to be able to provide the babies with milk uncontaminated by seeds, which the very young babies would be unable to digest. The hatchlings are fed on pure crop milk for the first week or so of life. After this the parents begin to introduce a proportion of adult food, softened by spending time in the moist conditions of the adult crop, into the mix fed to the squabs, until by the end of the second week they are being fed entirely on softened adult food.
After I uncover the bird cages each morning, I usually see the parents begin feeding their babies. I've tried to get a video of this process, but they quit feeding when I open the door to the cage. So I took this video through the bars of the cage.
In this video, the babies are 9 days old. I watched momma feeding them both at the same time, wondering how she did it. I thought she put her beak into theirs, but I learned that they put their beaks inside hers. I'm guessing that the bobbing head is caused by the effort to regurgitate the pigeon milk which she feeds them. The father, by the way, is an equal partner and sets the nest as well as feeds the babies.