Dolphins are mammals that produce milk to nourish their young. This underwater nursing process is an adaptation, allowing mothers to provide sustenance to their calves. Their unique physiology enables them to carry out this function while submerged.
The Mechanics of Underwater Nursing
Nursing underwater requires adaptations in both the mother and the calf. Female dolphins possess two mammary slits on their underside, which conceal inverted nipples for streamlining and preventing drag. When a calf is ready to feed, it nudges these mammary slits, signaling the mother to expose her nipples. The calf then positions its mouth around the nipple, often curling its tongue into a U-shaped or cone-like tube for a tight seal.
This unique tongue action helps prevent seawater from mixing with the milk. The mother dolphin then voluntarily ejects a stream of milk directly into the calf’s mouth, controlled by muscle contractions around the mammary glands. These nursing sessions are typically brief, lasting 5 to 10 seconds. In the first few weeks, a mother might lie on her side to help the calf locate the glands, or slow her swimming speed as the calf nurses alongside her. Calves must periodically surface for air, synchronizing their breathing with these quick nursing bouts.
The Nutritional Uniqueness of Dolphin Milk
Dolphin milk is formulated to meet the rapid growth and energy demands of a calf in a marine environment. Unlike terrestrial mammal milk, it is rich in fat and protein, with low water content. Fat content can be 33% to 40%, while water content is around 58%. This high-fat composition provides the energy needed for quick development and building a thick layer of blubber.
Blubber provides insulation against colder ocean temperatures, a layer newborn calves lack. The milk’s concentrated nature, similar to toothpaste or a milkshake, prevents it from dissolving quickly in seawater during nursing. Dolphin milk also contains lower lactose levels compared to human or cow’s milk. This nutritional profile supports the calf’s accelerated growth and helps it gain the size and strength needed for survival.
From Milk to Maturity: The Dolphin Calf’s Journey
Dolphin calves depend on their mother’s milk for an extended period, nursing typically lasting one to three years, though some may nurse for up to seven or eight years. During this time, the calf gradually transitions from a milk-dependent diet to consuming solid foods like fish and squid. Calves often begin to catch their own small fish around three to five months of age.
The mother-calf bond extends beyond providing nourishment. Mothers teach their calves survival skills, including hunting techniques, navigation, and social behaviors within the pod. Calves often swim in their mother’s slipstream, a low-pressure area that reduces their energy expenditure, allowing them to keep pace with the group. This prolonged maternal care and learning is important for a calf’s development and independence in the marine world.