Crop milk is a secretion from the crop organ of parent birds that is regurgitated to young offspring. It is an emulsion of fat and protein that provides nutrition for altricial chicks that are hatched blind, naked, and helpless.

What is the Crop Organ?

The crop is an enlarged part of the esophagus in birds. It serves as a storage pouch where food is moistened before passing further down the digestive tract.

The crop is located near the bottom of the neck, right before the entrance to the stomach. When full of food, it creates a bulge in the neck area.

The crop allows birds to quickly down food to be stored and eaten later. This is important for species that need to consume a lot of food rapidly. Having a crop pouch lets them eat more at one time than would fit directly into the stomach.

The stored food is later brought back up from the crop and rechewed before fully passing through the bird’s digestive system.

What is Crop Milk?

Crop milk is a unique substance that both male and female pigeons, doves, and flamingos produce in their crop to feed newly hatched chicks.

It is not like the milk of mammals. Crop milk is an emulsion of fat and protein. The fat provides a rich energy source and the proteins supply essential amino acids for growth and development.

Crop milk is made of concentrated nutrients manufactured by both parents. It does not contain lactose or casein like mammalian milk. The exact components can vary by species, but proteins make up 15-30% and fats comprise 50-70%. There are also immune molecules and carotenoids for pigmentation.

The crop milk is produced by sloughing off of fluid-filled epithelial cells that line the crop. This allows the high-energy crop milk to rapidly develop without direct blood supply.

The milk-like substance is regurgitated for hatchlings to ingest. In pigeons, both the male and female take turns feeding the young. The chicks insert their beak into the parent’s mouth to stimulate regurgitation of crop milk.

Why Do Some Birds Make Crop Milk?

Crop milk provides an evolutionarily advanced way for certain birds to nourish their vulnerable hatchlings. Species that need to produce precocial young developed the ability to synthesize crop milk.

Precocial birds are those whose chicks hatch covered in down feathers, with open eyes, and are mobile shortly after birth. They must rapidly grow and develop to become independent.

Crop milk gives an energy and nutrient boost. It is the sole food source for the first few days of life until chicks transition to seeds or insects. Without crop milk, precocial hatchlings would not survive.

Some examples of precocial species that depend on crop milk include:

• Pigeons
• Doves
• Flamingos
• Penguins
• Cormorants
• Plovers
• Rheas

For altricial species whose young hatch naked, blind, and helpless, crop milk production is not necessary. Those chicks grow more slowly and are fed by parents for an extended duration.

How is Crop Milk Produced?

The crop lining sheds nutritive cells in response to the hormone prolactin. Both male and female birds develop the ability to produce crop milk when they reach reproductive maturity.

The mechanism of crop milk synthesis is not fully understood but involves prolactin signaling on crop epithelial cells. This stimulates the cells to proliferate and fill with lipids and proteins.

The fluid-filled cells become engorged and detached from the epithelium. They slough off the lining, creating a nutritious secretion. The concentrated mixture of fat and protein resembles milk.

Hormone levels peak just after eggs hatch to maximize food availability. In pigeons, prolactin levels are highest during the first week post-hatching, resulting in copious crop milk output.

The crop has a direct blood supply during the period of crop milk production. This allows efficient transfer of nutrients from the circulation into the crop sac for crop milk generation.

Once the hatchlings are older, prolactin levels decrease, and the crop lining changes to reduce crop milk synthesis. The chicks simultaneously begin eating normal food.

How is Crop Milk Fed to Chicks?

Parent birds use their muscular crop organ to regurgitate the crop milk for newly hatched chicks. The hatchlings beg and bob their heads, signaling the adult pigeon for food. This stimulates regurgitation of the nutrient-rich crop milk.

Chicks insert their beak inside the parent’s mouth to eat the curdled emulsion. The begging behavior ensures they are correctly positioned to swallow each morsel.

Both male and female pigeons take turns feeding their young. Frequent feedings continue around the clock in the first week of life. The crop milk meals steadily decrease as the chicks mature and transition to seeds and grit.

Parent flamingos also produce crop milk and drip feed it directly into the chick’s mouth. Penguin chicks consume crop milk secreted from both parents’ crops for their first 2-3 weeks of life.

What is the Purpose of Crop Milk?

Crop milk provides essential nourishment to support growth and development in newborn chicks. It offers the perfect food source for precocial young that must rapidly mature.

The concentrated nutrition gives more energy than the parent bird could provide by collecting food. Crop milk contains up to twice the calories and three times the protein of regular bird milk.

The rich emulsion helps chicks grow quickly to become independent. Without crop milk, they would not survive the vulnerable neonatal period.

Benefits include:

• High calorie and protein content for rapid growth
• Antimicrobial agents to protect from infection
• Carotenoids for immune function and flamingo pigmentation
• Growth promoting hormones and vesicles
• Complete source of amino acids for development
• Easy for hatchlings to digest and absorb

Within just one week, a crop milk-fed hatchling can increase its body mass up to 400%! The nutritious fluid is essential for birds with precocial offspring requiring substantial early development.

What is Pigeon Milk?

Pigeon milk is a type of crop milk produced by both male and female parent pigeons to feed newly hatched squabs.

Pigeon milk contains over 60% fat and 15-20% protein. The high lipid concentration provides more calories for fast growth. Immune molecules and growth promoters are also present.

Pigeon milk is first secreted around 3 days before eggs are laid. It is initially thick and yellowish, but the consistency changes to a lighter, more fluid texture after hatching.

Both parents continue producing the milk-like substance for up to 10 days post-hatching. Squabs can increase body weight tenfold in just 7-10 days when fed nutritious pigeon milk.

Pigeon milk is produced in progressively smaller quantities as the squabs grow. By two weeks old, they transition to seeds, grains, and insects for food.

Do Flamingos Make Crop Milk?

Yes, flamingos are one of the bird species that produce crop milk. Both male and female flamingos synthesize crop milk in their esophageal pouch.

The nutritious fluid contains over half lipids and around 15% protein. It also has essential carotenoids that give flamingo chicks their colorful pink feathers.

Parent flamingos drip crop milk directly into the hatchling’s mouth. The chick sticks its head inside the adult’s bill and pumps its neck to get milk.

Crop milk production begins with egg laying and lasts for 10-14 days after hatching. It helps the chicks grow strong and healthy. Without it, they wouldn’t survive.

The flamingo’s crop has a direct blood supply only during the time of crop milk secretion. This allows efficient transfer of nutrients into the milk-like emulsion.

Flamingo crop milk helps the chicks achieve the massive weight gain crucial for precocial development. With proper nutrition, hatchling flamingos double in size in just two weeks!

Do Penguins Make Crop Milk?

Yes, both male and female penguins produce a form of crop milk to nourish their chicks. Penguin crop milk is very high in fat, with around 66% lipid content.

Emperor penguins secrete crop milk for almost two months while incubating eggs. Then, after hatching, they continue producing it for 2-3 weeks to feed chicks.

Since penguins don’t have typical crop pouches, the milk-like substance is made in their esophagus. The nutritious fluid is regurgitated like regular crop milk.

Parents take turns feeding their hatchling by allowing it to reach in their mouth and ingest the thick, yellowish crop milk.

The concentrated nutrition helps penguin chicks grow and develop protective feathers. Without crop milk, the vulnerable chicks would not survive the harsh Antarctic winter.

When Do Birds Stop Making Crop Milk?

Birds gradually decrease crop milk production over a chick’s first few weeks of life. The young offspring simultaneously begins eating more normal food.

In pigeons, crop milk synthesis starts declining around 7-10 days post-hatching. Prolactin levels decrease, and the crop lining changes.

For flamingos, the richest crop milk production lasts around two weeks after eggs hatch. Penguin parents secrete crop milk for 2-3 weeks post-hatching.

The chicks’ begging behavior decreases as crop milk hand-feedings become less frequent. By two to three weeks old, the babies’ diet is mostly adult food like seeds or shrimp.

The timing allows a gradual transition to independent feeding. As crop milk lessens, the hatchlings are developmentally ready for new food sources.

Weaning off crop milk depends on the species but generally occurs between 2-4 weeks post-hatching. The young chicks have grown enough to survive without the nutritional fluid.

Do Both Parents Make Crop Milk?

In most bird species, both the male and female parent produce crop milk to nourish their chicks.

Pigeons are a prime example. Male and female pigeons take turns feeding regurgitated crop milk to their hatchlings multiple times a day.

Penguins and flamingos also both secret crop milk. Parent flamingos drip it into the chick’s mouth. And penguin parents shed esophageal cells to generate the fat-rich substance.

Male budgerigars, however, do not produce crop milk. Only the mother budgie synthesizes the crop milk to nourish hatchlings.

Evolutionarily, biparental crop milk feeding probably boosted reproductive success. The chicks get fed more frequently and double the nutrition.

Both parents making crop milk provides insurance if one dies. The remaining parent can still produce enough crop milk to raise the brood solo.

What Animals Produce Milk Besides Mammals?

Only mammals make true milk that requires lactation for nourishing newborns. But some birds synthesize a milk-like nutritional fluid in their crop organ.

Bird species that produce crop milk include:

• Pigeons
• Doves
• Flamingos
• Penguins
• Shearwaters
• Cormorants
• Budgerigars
• Columbids
• Rheas

Researchers have also identified primitive forms of lactation-like nutrition in certain fish and invertebrates.

Some fish species produce milk-like skin secretions to nourish eggs and new hatchlings. Certain rove beetles nourish larvae with glandular secretions.

But birds are the only non-mammals who fully developed the ability to make a true milk-like nutritional fluid. Crop milk mimics all the key features of mammalian lactation.

Do Male Seahorses Produce Milk?

No, male seahorses do not create a milk-like substance. But they do provide a form of “male pregnancy” and give birth to offspring!

Seahorses exhibit a unique reproductive strategy where the male carries the eggs in a brood pouch. The female deposits eggs into his pouch, and he fertilizes them internally.

The embryonic seahorses then develop fully inside the male’s pouch. He provides oxygen, nutrients, and protection.

When development completes, the male enters labor and gives birth, ejecting tiny baby seahorses from his pouch into the water.

So while male seahorses don’t lactate or make milk, their pouch allows them to become pregnant and provide nutrients to developing embryos!

Key Takeaways on Crop Milk:

• Crop milk is a fat and protein emulsion secreted by the crop of certain birds
• It serves as the sole food for newly hatched chicks of precocial species
• Both male and female parents can produce the nutrient-rich substance
• Pigeon milk, flamingo milk, and penguin milk are all forms of crop milk
• It is regurgitated into hatchlings’ mouths, providing nutrition for growth
• Crop milk production decreases as chicks mature and transition to normal food
• Without crop milk, vulnerable chicks of altricial species would not survive

What Is Pigeon Milk?

Pigeon milk is a unique substance produced by both mother and father pigeons to feed newly hatched chicks called squabs. This form of crop milk provides essential nutrients and immune factors to support the rapid growth and development of baby pigeons.

What is Pigeon Milk Made Of?

Pigeon milk consists of nutritive fluids secreted from the crop lining of parent birds. It contains approximately 65% fat and 15-20% protein.

The main components of pigeon milk include:

• Fats and fatty acids – Provides concentrated calories for energy and growth.
• Proteins – Supply essential amino acids for development. Mainly immunoglobulins and albumin.
• Antimicrobials – Protect squabs from infections.
• Growth promoters – Hormones and growth factors to facilitate maturation.
• Immune factors – Maternal antibodies and white blood cells.
• Carotenoids – Pigmentation for the squab.
• Electrolytes – Ions like sodium, potassium, and chloride.
• Prebiotics – Support digestive health.

The balance of fat to protein in pigeon milk can vary over time. The earliest secretions are more viscous and yellowish, with over 60% fat. It becomes more dilute and fluid after hatching.

The concentrations provide the perfect nutrition profile to give squabs an energetic boost. The rich array of proteins, protective factors, and micronutrients supplies everything a growing chick needs.

How is Pigeon Milk Produced?

Pigeon milk comes from both the male and female parent. Production begins a few days before eggs are laid in preparation for hatching.

The mechanism involves the hormone prolactin. As prolactin levels rise, it acts on the epithelial cells lining the crop sac.

This stimulation causes the cells to proliferate and fill with lipids and proteins. The cells become engorged with fluid and detach from the epithelium.

These secretory cells are sloughed off into the crop sac where they accumulate and are regurgitated as pigeon milk.

The lining of the crop transitions from a hardened stratified layer to a softened simple columnar epithelium. This facilitates increased nutrient transfer into the crop cells to create the milk fluid.

Parents can produce up to 25mL of nutrient-rich crop milk per day to hand-feed squabs. Both produce equal amounts and continue secreting for up to 10 days.

How Do Squabs Get Fed Pigeon Milk?

Parent pigeons use their muscular crop organ to regurgitate the concentrated crop milk fluid to feed newly hatched squabs.

The nestling squabs beg for food by bobbing their heads vigorously. This signaling stimulates the parents to bring up the nutrient-rich crop milk.

The hungry baby sticks its beak inside the adult’s mouth. The parent then regurgitates the milk-like substance directly into the squab’s mouth.

Both mother and father pigeons take turns feeding the crop milk numerous times a day. The frequent, small meals provide a continual food source.

As the squabs grow, the intervals between feedings increase. By two weeks old, the babies are eating regurgitated seeds and grains.

Why Do Pigeons Produce Crop Milk?

Pigeon milk provides a perfectly adapted nutrition source to give squabs an energetic boost after hatching. This helps pigeons have a reproductive advantage as precocial birds.

Precocial species like pigeons have chicks that hatch covered in down, with eyes open, and able to move about. But they are vulnerable and need to develop quickly.

Pigeon milk allows rapid growth – a squab can increase its body mass tenfold in just over a week! Without the crop milk, newborns would not survive.

The concentrated nutrition supplies the building blocks need for growth. Pigeon milk contains over double the calories and triple the protein compared to regular bird milk.

Both parents producing crop milk improves feeding frequency. More crop milk feedings result in faster growth and healthier squabs.

When Does Pigeon Milk Production Stop?

Pigeon parents start decreasing crop milk production around 7-10 days after eggs hatch. Squabs also beg for feedings less frequently.

Prolactin levels begin to drop, and the crop lining changes to reduce secretion capacity. The squabs’ diet shifts to more regurgitated seeds and insects.

By two weeks old, the parent pigeons are no longer producing crop milk. The babies rely entirely on soaked seeds, grains, greens, and bugs brought by their parents.

Weaning occurs by 14-30 days post-hatching once squabs can digest solid foods. The crop milk enabled fast development to facilitate the transition to independence.

What Happens Without Pigeon Milk?

Pigeon squabs depend completely on crop milk for the first week of life. Without it, they would not get adequate nutrition and energy.

Squabs need crop milk’s high fat and protein content for the rapid growth that occurs in the first days after hatching. Nestlings can increase body weight tenfold in just one week!

Insufficient crop milk would stunt growth and development. Squabs would likely die from malnutrition, dehydration, or infection without the antibody protection crop milk provides.

Lack of pigeon milk may also contribute to “fading syndrome” where baby pigeons fail to thrive and die for no apparent reason.

Supplementing hatchlings with puppy formula can help survival but does not contain the ideal nutrition profile pigeon milk provides.

Key Takeaways on Pigeon Milk

• Pigeon milk is a form of