The answer to whether birds drink milk from their mother is no; birds do not nurse their young in the same way mammals do. Mammalian milk is a specialized secretion produced by mammary glands, a unique anatomical feature that birds completely lack. The class Aves, which includes all birds, has evolved distinct reproductive and parental care strategies that do not involve the production of true milk.
Why Birds Cannot Produce Milk
The inability of birds to produce true milk stems from the evolutionary divide between the class Aves and the class Mammalia. Mammals are defined by the presence of mammary glands, which are complex structures that secrete milk, a carbohydrate-rich emulsion containing lactose, directly to the young.
Birds evolved along a separate lineage and lack the necessary anatomy for glandular milk production. Avian physiology is heavily influenced by the demands of flight, favoring a lightweight body structure. Carrying the added weight and metabolic cost of milk-producing mammary glands would present a disadvantage for most flying species.
Standard Avian Parental Feeding
The vast majority of bird species feed their young using methods that rely on external food sources rather than an internal secretion. One common technique is regurgitation, where a parent swallows food, partially digests it, and then brings it back up to deposit directly into the chick’s mouth. This method delivers a mash of insects, seeds, or other foraged material.
The developmental stage of the hatchling dictates the feeding approach. Altricial young, such as songbirds, are born helpless, requiring constant feeding from their parents until they fledge. Conversely, precocial young, like ducks and chickens, are born with feathers and open eyes, and can often begin foraging for themselves within hours of hatching. Parents of precocial species still provide protection, but the feeding demands are less intensive than for altricial chicks.
The Phenomenon of Crop Milk
A few exceptional bird species have evolved a unique secretion known as “crop milk” to nourish their young. This substance is often confused with mammalian milk, but it is not true milk because it does not come from mammary glands and contains no lactose. The primary producers are pigeons and doves, but it is also found in flamingos and the male Emperor penguin.
Crop milk is a holocrine secretion produced by the sloughing off and detachment of fat-filled epithelial cells from the lining of the parent’s crop, a sac-like pouch used for food storage. In pigeons, this fatty, curd-like substance is extremely rich in nutrients, containing high levels of both protein and fat. Production is triggered by the hormone prolactin, the same hormone that regulates lactation in mammals, demonstrating convergent evolution for parental feeding.
Both male and female pigeons and doves produce crop milk, which is regurgitated directly into the mouth of the squab during the first week or two of life. The milk of flamingos and Emperor penguins differs slightly. Flamingo crop milk, which is reddish due to carotenoids, is produced from the entire upper digestive tract, while the Emperor penguin father produces a temporary, protein-rich secretion from his esophagus. This nutrient-dense fluid allows the chicks of these specialized species to grow rapidly.