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Several living animals feed their young with a milk-like secretion even though they have no mammary glands. The best-documented examples are pigeons and doves, flamingos, emperor penguins, and the egg-laying caecilian Siphonops annulatus. The birds make a secretion in the upper digestive tract, usually called crop milk. Female Siphonops annulatus makes a different, lipid-rich secretion in glands of the oviduct and releases it through the vent.
These systems perform a similar job to mammalian lactation—delivering concentrated nourishment to dependent offspring—but they are not mammalian milk and do not use mammary tissue. “Milk-like” is therefore the most accurate umbrella term.
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The documented animals
Pigeons and doves
Pigeons and doves produce crop milk in a specialized pouch of the upper digestive tract called the crop. After hatching, a squab receives this secretion directly from its parent’s mouth. The parent does not obtain it from a mammary gland; epithelial cells lining the crop change under hormonal stimulation and form the nutritive material.
Prolactin is the key hormonal signal identified for this process. As the breeding cycle approaches feeding, the crop lining thickens and its specialized cells produce the secretion. Both male and female pigeons and doves can make crop milk, so feeding is not restricted to the mother. Parents regurgitate it for newly hatched young, when the chicks are too immature to handle ordinary seeds or other solid food.
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“Crop milk” describes its location and function, not a claim that it is chemically or anatomically identical to cow’s milk or human breast milk. It is a temporary parental food produced for a particular stage of chick development.
Flamingos
Flamingo parents also feed their chicks a crop-milk-like secretion from the upper digestive tract. Ornithology and zoo sources commonly use the term “crop milk” for this food, although descriptions differ in how narrowly they define the tissue involved. Some accounts refer to the crop specifically; others describe a secretion originating in the upper digestive tract.
Both male and female flamingos feed chicks. The parent supplies the secretion directly to the chick rather than nursing through a nipple. The secretion supports the chick during its early dependent period, before the young bird is fully independent in feeding.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesThe flamingo example should be stated with that anatomical qualification. The evidence supports a milk-like upper-digestive-tract secretion and parental feeding, but the detailed cellular process is not as thoroughly described as it is for pigeons and doves.
Emperor penguins
Male emperor penguins are reported to produce crop milk for their young. This is another bird example of a milk-like food made without mammary glands. The available descriptions establish the example and identify the male parent, but they do not provide the same level of physiological detail available for pigeon crop milk.
It is therefore safest to say that emperor penguins are documented crop-milk producers, with the cited report specifically identifying males, rather than to assume that every aspect of their secretion is understood or that both sexes produce it in the same way.
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The caecilian Siphonops annulatus
Siphonops annulatus is an egg-laying caecilian, a limbless amphibian that resembles a burrowing worm. Its feeding system is fundamentally different from bird crop milk. A female develops enlarged glands in the lining of her oviduct. Those glands produce a lipid-rich, milk-like secretion that leaves the body through the vent, the common external opening of the digestive, urinary and reproductive tracts in this animal.
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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Hatchlings consume the secretion from the female. Observations recorded provisioning over approximately two months, showing that the secretion is not a one-time coating of the eggs but an active post-hatching food source. The tissue involved is oviduct epithelium, not a crop and not a mammary gland. This makes the caecilian an especially clear example of convergent parental provisioning: a non-mammal evolved a secretion used to feed young, but through a different organ and route.
How the systems compare
The word “milk” can hide important biological differences. The useful comparison is the tissue that produces the secretion, how the young receive it, and which parent provides it.
| Animal group | Producing tissue | How young receive the food | Parent identified in the evidence |
|---|---|---|---|
| Pigeons and doves | Specialized epithelial cells lining the crop sac | Parents regurgitate crop milk to newly hatched squabs | Both sexes produce and feed it |
| Flamingos | Upper digestive tract; sources use “crop milk” broadly | Parents feed chicks the crop-milk-like secretion | Both sexes feed chicks |
| Emperor penguins | Reported as crop milk; detailed physiology is limited | Milk-like food is supplied to the young | Male emperor penguins are identified |
| Siphonops annulatus | Hypertrophied glands in the oviduct epithelium | Hatchlings consume secretion released through the vent | Female provides it |
This table does not rank the systems by “similarity” to mammalian lactation. Similarity depends on the feature being measured. Crop milk resembles mammalian lactation in its role as a specialized early food, while the caecilian secretion differs in both anatomy and delivery. No single scale captures all of those dimensions.
What mammary glands normally do—and what these animals replace
Mammary glands are specialized skin glands that secrete milk through ducts, usually from nipples or comparable openings. Mammalian young commonly attach to that outlet and suckle. The defining feature is the glandular tissue and its duct system, not simply the presence of a pale or nutritious liquid called milk.
Birds lack mammary glands, nipples and the mammalian breast structure. In pigeons and doves, the crop lining temporarily becomes a secretory tissue instead. Hormonal signals associated with reproduction, especially prolactin, coordinate that change. The crop is ordinarily a storage area in the digestive tract; during chick-rearing it also becomes a source of parental food.
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In Siphonops annulatus, the oviduct is the source. The female’s reproductive tract develops enlarged secretory glands, and the secretion is released through the vent for hatchlings to consume. That arrangement is not a modified mammalian breast. It is a separate evolutionary solution built from amphibian anatomy.
How the young obtain the secretion
Birds: direct feeding from the parent
Newly hatched pigeons and doves receive crop milk by regurgitation. Their parents bring the secretion up from the crop and pass it to the squabs. The behavior allows the adults to provide a concentrated food while the chicks are still unable to process the diet of older birds.
Flamingo parents likewise deliver their upper-digestive-tract secretion to chicks. Sources differ in whether they reserve “crop milk” for a specific crop tissue or use it as a functional description, so the route is best described as direct parental feeding rather than as nursing in the mammalian sense.
Reports of emperor-penguin crop milk establish the same general pattern of a parent supplying a milk-like food, but the reviewed evidence does not give a detailed account of the secretion’s cellular origin or feeding mechanics. Those details should not be filled in by assuming that all bird examples work identically.
Caecilians: a secretion available at the vent
Caecilian hatchlings feed from the female’s vent, where the oviduct-derived secretion exits. The observation of feeding over about two months indicates sustained maternal provisioning after hatching. Because the secretion is lipid-rich and comes from oviduct glands, it should not be described as crop milk or as a bird-like process.
Why birds make crop milk
Crop milk solves a timing problem. A hatchling needs food immediately, but its digestive system and feeding behavior are not yet suited to the adult diet. A parent can instead produce a temporary secretion inside its own body and transfer it directly to the chick.
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In pigeons and doves, the crop’s epithelial cells are the biological “factory.” Prolactin stimulates the change, and both parents can participate. This arrangement spreads the feeding work across the pair and ensures that a newly hatched squab has access to food even when one parent is away.
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Flamingo and emperor-penguin examples show that the same broad function has evolved in other birds. However, the evidence is not equally detailed for every species. The existence of a milk-like secretion is well documented in the named examples; the exact composition, cellular pathway and hormonal control are not established to the same degree for all of them.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What “milk-like” does—and does not—mean
- It means a parental secretion used to nourish dependent young. The term emphasizes function and appearance or consistency, not mammalian anatomy.
- It does not mean the animal has mammary glands. Pigeons, flamingos and emperor penguins use upper-digestive-tract tissues; Siphonops annulatus uses oviduct glands.
- It does not mean all examples share the same chemistry. The caecilian secretion is described as lipid-rich, while the cited evidence does not establish one common composition for every bird secretion.
- It does not mean every bird makes milk. The documented examples are specific groups, not a property of birds as a whole.
- It does not provide a complete species count. The examples are well documented, but no comprehensive inventory of all living animals with comparable systems is established here.
Which parent feeds the young?
Parental sex is one of the clearest differences among the examples. In pigeons and doves, both sexes produce crop milk and feed the chicks. Flamingo sources likewise describe both sexes feeding their young. The emperor-penguin report specifically identifies males as crop-milk producers, and the available account does not establish an equivalent production role for females.
In Siphonops annulatus, the female provides the oviduct secretion. The maternal system is therefore anatomically tied to the female reproductive tract, unlike pigeon crop milk, which can be produced by either parent.
These patterns show that milk-like provisioning is compatible with several forms of parental care. It can be shared by a pair, concentrated in one sex, or linked to a female’s reproductive anatomy.
Common questions answered precisely
Do birds produce milk?
Some birds do produce a milk-like secretion. Pigeons and doves are the clearest example, and flamingos and emperor penguins are also documented. It is crop milk or an upper-digestive-tract secretion, not mammalian milk made by mammary glands.
Are pigeons the only birds that make milk?
No. Pigeons and doves are the best-known examples, but flamingos and emperor penguins are also included among documented crop-milk producers. The physiology is not equally well characterized in all three groups.
Is caecilian milk the same as bird crop milk?
No. Caecilian milk-like secretion comes from hypertrophied oviduct glands and exits through the vent. Bird crop milk comes from specialized upper-digestive-tract tissue. They are functionally comparable foods, not the same biological product.
How many animals can feed their young this way?
No reliable total can be given from the documented evidence. It establishes several examples rather than a complete global inventory, so a precise number would overstate what is known.
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These animals demonstrate convergent solutions to a common problem: offspring often need a concentrated, easily delivered food before they can use the adult diet. Mammals solved that problem with mammary glands. Some birds recruited the crop or nearby upper digestive tract. A caecilian recruited glands in the oviduct.
The comparison is valuable precisely because the structures differ. Calling all of the secretions “milk” highlights their role in parental nourishment, while adding “crop” or “oviduct” preserves the anatomical distinction. A careful explanation should use both parts of that description instead of treating every non-mammalian secretion as a hidden form of mammalian lactation.
Bottom line
Pigeons and doves, flamingos, emperor penguins and the caecilian Siphonops annulatus all provide documented examples of animals feeding young with milk-like secretions without mammary glands. Pigeon and dove crop milk is made by crop epithelial cells under prolactin stimulation and supplied by both parents. Flamingos use a comparable upper-digestive-tract secretion, emperor-penguin crop milk is reported particularly for males, and female Siphonops annulatus produces lipid-rich oviduct secretion that exits through the vent. The shared function is real; the organs and mechanisms are not interchangeable.
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