Nursing

All whale species nurse their young for several months, but the exact duration varies from one species to another. Females have two nipples concealed in two small slits on either side of the genital slit, below the belly. Cetaceans lack sucking muscles. Instead, the calf stimulates the nipple by putting pressure on it and milk is then ejected into its mouth. The edge of its tongue is lined with petal-like extensions that are believed to improve suction and even serve to channel the milk toward the throat. With age and as the calf is weaned, these “petals” disappear.

Depending on the species, whale milk contains between 13 and 53% fat. This is much more than in land mammals, which allows the calf to grow quickly. A blue whale calf, for example, puts on 80 kg a day. Females produce milk from the fat reserves under their skin.

In baleen whales, milk is generally richer and nursing shorter-lasting than in toothed whales (several months vs. 1-2 years). Additionally, in most baleen species, females do not eat for at least the first few months of lactation. A female that feeds often has to leave her young on the surface, where it is vulnerable to predators, so fasting helps her stay close to her young at all times.

Calf in tow

In cetaceans, maternal care is long-lasting. Calves and juveniles stay close to their mothers’ sides for a long time, even if they are able to feed themselves. Belugas remain near their mothers for three years, sometimes even longer. During this period, mother and calf develop a strong bond, which is essential for the offspring’s survival.

The best known maternal care in whales is where the female places the calf close to her side while swimming. In this position, called “echelon”, the calf takes advantage of it’s mother’s wake the same way a cyclist at the head of the group makes it easier on those trailing behind. This hydrodynamic advantage for the calf comes at the expense of an additional drag force for its mother. The latter must therefore exert more effort when swimming.

Watching over others’ offspring

Although mothers do take care of their own offspring, certain females within the group may also temporarily pitch in. These “babysitters” can be a sister, an aunt, a cousin or another female that is not even related. If watching a friend’s baby is common for humans, it is still somewhat of an enigma when it comes to cetaceans.

Several hypotheses may explain why certain whales – including sperm whales, belugas and pilot whales – engage in allomaternal care (care provided by a female other than the mother).

Could it be a question of reciprocity? If one female assists a calf belonging to another female, the latter might be more inclined to return the favour by caring for her helper’s future offspring. This “whale-sitting” might also just be how young females practise to be mothers.

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