Crop milk is a secretion from the lining of the crop of parent birds that is regurgitated to young birds. They are found among all pigeons and doves where they are referred to as pigeon milk. Crop milk is also produced by flamingos and some penguins.
Comparison to mammalian milk
Crop milk bears little resemblance to mammalian milk, the former being a semi-solid substance somewhat like pale yellow cottage cheese. It is extremely high in protein and fat, containing higher levels than cow or human milk. It has also been shown to contain anti-oxidants and immune-enhancing factors. Like mammalian milk, crop milk contains IgA antibodies. It also contains some bacteria. Unlike mammalian milk, which is an emulsion, pigeon crop milk consists of a suspension of protein rich and fat rich cells that proliferate and detach from the lining of the crop. In pigeons and flamingoes, both the male and female adult produce crop milk and share in the feeding and care of the young. In penguins only the males lactate. Lactation in birds is also controlled by prolactin, which is the same hormone in mammals.
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 squabs (baby pigeons and doves) with milk uncontaminated by seeds, which the very young squabs would be unable to digest. The baby squabs 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.
Pigeons normally lay two eggs. If one egg fails to hatch, the surviving squab gets the advantage of a supply of crop milk sufficient for two squabs, and by the end of the first week it is almost as big as two "normal" squabs would be.
Hand-rearing pigeon squabs
The very high nutrient concentration of pigeon's milk makes it difficult to devise an artificial substitute for hand-rearing squabs. Various proprietary mixes are available. A good home-made mix can be made from equal quantities of dehydrated dried pure soy protein (with no added salt, flavorings, preservatives etc.) and soy-based dairy-free butter-substitute (ordinary dairy butter is not suitable, as young squabs' digestive systems cannot cope with dairy products). This is made into a runny paste with a little water, a tiny crumb of a multivitamin tablet and a tiny pinch of chalk (which is necessary for bone development to avoid splay-leg). The crop should be allowed to empty completely between feedings. With care and gentleness, it is possible to raise a pigeon on this mix from the moment of hatching.
- In Animal Crossing: Wild World for the Nintendo DS and Animal Crossing: City Folk for the Wii, a character named Brewster uses it as an ingredient when serving coffee to long-time customers.
- In the reality TV series Flavor of Love during Season 2, the father of Deelishis requests a carton of pigeon milk at dinner.
- Ptasie mleczko (Polish: bird milk) is the name of Polish candy, which variations are also popular in Eastern Europe countries as Ptichye Moloko (Russian: птичье молоко), ptashyne moloko (Ukrainian: птaшине молоко).
- Levi, Wendell (1977). The Pigeon. Sumter, S.C.: Levi Publishing Co, Inc. ISBN 0-85390-013-2.
- Silver, Rae (1984). "Prolactin and Parenting in the Pigeon Family". The Journal of Experimental Zoology 232 (3): 617–625. doi:10.1002/jez.1402320330. PMID 6394702.
- Eraud, C., Dorie, A., Jacquet, A. and Faivre, B. (2008). "The crop milk: a potential new route for carotenoid-mediated parental effects". Journal of Avian Biology 39 (2): 247–251. doi:10.1111/j.0908-8857.2008.04053.x.
- Ehrlich, Paul R.; Dobkin, David S. and Wheye, Darryl (1988) Bird Milk. stanford.edu
- "Mysteries of pigeon milk explained" Retrieved September 22, 2011
- Gillespie, M. J.; Stanley, D.; Chen, H.; Donald, J. A.; Nicholas, K. R.; Moore, R. J.; Crowley, T. M. (2012). "Functional Similarities between Pigeon 'Milk' and Mammalian Milk: Induction of Immune Gene Expression and Modification of the Microbiota". In Salmon, Henri. PLoS ONE 7 (10): e48363. doi:10.1371/journal.pone.0048363.
- Gillespie, M. J.; Haring, V. R.; McColl, K. A.; Monaghan, P.; Donald, J. A.; Nicholas, K. R.; Moore, R. J.; Crowley, T. M. (2011). "Histological and global gene expression analysis of the 'lactating' pigeon crop". BMC Genomics 12: 452. doi:10.1186/1471-2164-12-452. PMC 3191541. PMID 21929790.