Whales, like all mammals, nourish their young through nursing. This process is fundamental for the early development and survival of whale calves. Despite living entirely in water, female whales provide milk to their offspring in the marine environment.
How Whales Nurse Underwater
Nursing underwater presents challenges, which whales overcome through specialized anatomical and behavioral adaptations. Female whales possess mammary glands concealed within mammary slits on their underside, near the genital slit. These slits house retractable nipples that become accessible when the calf is ready to nurse.
When a calf is ready to nurse, it nudges the mother’s belly, signaling its intent. The mother then actively ejects milk into the calf’s mouth through muscular contractions of her mammary glands. This active ejection is necessary because whale calves lack the strong sucking muscles and lips found in terrestrial mammals.
The calf positions itself close to the mother, often belly to belly. Some research suggests calves may curl their tongues or have petal-like extensions to help channel the milk and create a seal, preventing dilution with seawater. This process is quick, lasting only a short period to minimize the calf’s time underwater without breathing.
The Unique Properties of Whale Milk
Whale milk possesses distinct properties, making it ideal for calves in an aquatic environment. It has an extremely high fat content, often ranging from 13% to 53%, with some species like blue whales (35-50%) or humpback whales (45-60%) having even higher levels. This concentrated energy source is significantly greater than that found in terrestrial mammal milk. The milk also contains a high protein content, supporting the development of tissues and muscles in the growing calf.
Its very low water content gives whale milk a thick consistency, often described as similar to cottage cheese or yogurt. This thickness helps prevent the milk from dissolving or dispersing in the surrounding seawater during nursing. The milk’s composition, including minimal or absent lactose, is adapted to the calf’s digestive system. This nutrient-dense milk facilitates the rapid accumulation of blubber, a thick layer of fat for insulation against cold ocean waters and for buoyancy.
The Importance of Nursing for Calf Survival
The nursing period is a fundamental stage in a whale calf’s life. Its duration varies significantly among different whale species, ranging from a few months to over two years. For instance, baleen whales generally nurse for 6 to 9 months, while some toothed whales, like belugas, can nurse for 20 to 30 months.
The milk supports a rapid growth rate in calves. A blue whale calf, for example, can gain 80 to 100 kilograms per day while nursing. This weight gain is primarily due to the accumulation of blubber, which provides insulation against the cold ocean and serves as an energy reserve. Nursing also transfers antibodies from the mother to the calf, providing passive immunity against diseases during its vulnerable early life. This period of dependency ensures the calf receives sufficient nutrition and protection before it becomes capable of foraging independently.