Doves, and all members of the Columbidae family, feed their young with a substance called “crop milk.” This nutrient-dense meal is produced within the crop, a pouch-like structure in the esophagus, and is the sole source of nutrition for newly hatched squabs. The process functions similarly to mammalian lactation, yet it is a non-glandular secretion unlike true milk.
The Biological Origin of Crop Milk
The production of crop milk is not a glandular secretion but a process of cellular shedding from the lining of the crop. The crop, normally a simple storage organ for food, undergoes a transformation in preparation for the young. This change is driven by the hormone prolactin, the same hormone that governs milk production in mammals.
Prolactin stimulates the growth and development of specialized epithelial cells that line the crop sac in both male and female parents. These cells become engorged with fat and protein, resulting in the thickening of the crop lining. When the squabs are ready to hatch, these fat-laden cells detach, or slough off, into the lumen of the crop, forming the semi-solid, curd-like substance known as crop milk.
This physiological change begins days before the eggs hatch, ensuring an immediate food supply for the nestlings. Both parents are involved in producing and delivering the crop milk, which aids in the successful and rapid growth of the young. The mechanism is classified as a holocrine secretion, meaning the entire cell is shed to become the secretion, rather than an apocrine secretion like mammalian milk.
Nutritional Makeup of Dove Milk
Crop milk is an energy-dense and protein-rich food source, tailored for the rapid development of the young. On a dry matter basis, it contains a high percentage of protein (45% to 55%) and an equally high fat content (38% to 48%). This composition is significantly higher in both protein and fat than cow or human milk.
The substance is a suspension of fat and protein-filled cells and notably contains virtually no carbohydrates, unlike mammalian milk. Beyond macronutrients, dove milk contains antioxidants, various minerals, and immune components, such as IgA antibodies. These components provide the nestling with passive immunity during its early stage of life.
The Feeding Process and Squab Development
The physical act of feeding is a direct and efficient method of nutrient delivery. The newly hatched squabs, or nestlings, instinctively stimulate the feeding process by inserting their beaks deep into the parent’s mouth. The parent then regurgitates the crop milk, effectively pumping the nutrient-rich substance directly into the squab’s own crop.
Both the male and female doves participate equally in this feeding duty, sharing the metabolic burden and ensuring a constant supply of food. This intense feeding regimen, fueled by the energy-dense crop milk, results in a rapid growth rate for the squabs. For the first week of life, the young are fed exclusively on this pure crop milk.
The rapid growth enabled by this diet is apparent in the squabs, who mature much faster than the young of many other avian species. Parents adjust the amount of food based on the young’s size, with the highest volume of crop milk being delivered around the fourth or fifth day after hatching. This system ensures the nestlings receive maximum nourishment during their initial period.
Moving to an Adult Diet
The transition from a pure milk diet to an adult diet of seeds and grains is a gradual process that begins around one week after hatching. As the squabs grow, the parents begin to mix small amounts of adult food, which has been softened in the parent’s crop, into the crop milk. This blending introduces the young bird’s digestive system to solid foods and marks the start of the weaning phase.
The production of crop milk in the parents begins to taper off when the squabs are between six and nine days old. By the end of the second week, the young are being fed almost entirely on softened seeds and other materials from the adult diet. Within a few weeks, often by the time they are ready to fledge, the squabs are consuming the same diet as the adult doves and are fully independent feeders.