Rosaflamingo-Küken - Fuetterung mit Kropfmilch

Crop milk is a secretion from the lining of the

crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydropon ...

of parent birds that is regurgitated to young birds. It is found among all pigeons and doves where it is referred to as pigeon milk. An analog to crop milk is also secreted from the esophagus of flamingos and the male

emperor penguin The emperor penguin (''Aptenodytes forsteri'') is the tallest and heaviest of all living penguin species and is endemic to Antarctica. The male and female are similar in plumage and size, reaching in length and weighing from . Feathers of t ...

Description

Crop milk bears little physical resemblance to

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

ian

milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...

. Crop milk is a semi-solid substance somewhat like pale yellow

cottage cheese Cottage cheese is a curdled milk product with a mild flavor and a creamy, non-homogeneous, soupy texture. It is made from skimmed milk by draining the cheese, as opposed to pressing it to make cheese curd—retaining some of the whey and keep ...

. It is extremely high in

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

and fat, containing higher levels than cow or human milk. A 1939 study of pigeon crop milk showed, however, that the substance did not contain carbohydrates. It has also been shown to contain anti-oxidants and immune-enhancing factors which contribute to milk immunity. Like mammalian milk, crop milk contains

IgA Iga may refer to: Arts and entertainment * Ambush at Iga Pass, a 1958 Japanese film * Iga no Kagemaru, Japanese manga series * Iga, a set of characters from the Japanese novel '' The Kouga Ninja Scrolls'' Biology * ''Iga'' (beetle), a g ...

antibodies. It also contains some bacteria. Unlike mammalian

, which is an

emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Alth ...

, pigeon crop milk consists of a suspension of protein-rich and fat-rich cells that proliferate and detach from the lining of the

. Lactation in birds is controlled by

prolactin Prolactin (PRL), also known as lactotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pi ...

, which is the same hormone that causes lactation in mammals.

Pigeons

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 grows at a significantly faster rate. Research suggests that a pair of breeding pigeons cannot produce enough crop milk to feed three squabs adequately, which explains why clutches are limited to two.

References

External links

Article on Bird Milk from stanford.edu

Article on the relationship between crop milk and clutch size in Mourning Doves (.pdf)

Smithsonian National Zoo article on Common Crowned Pigeon, includes paragraph on crop milk
{{Birds Domestic pigeons Bird anatomy Bird behavior Milk by animal de:Kropf#Kropfmilch