Baby whales are called calves. The gestation period in most whale species is 11 to 16 months. Generally a single young is born, tail first likely in order to prevent drowning, and twins are very rare. The newborn calf is usually one-quarter to a third the length of the mother.
The ‘baby’ stage runs from birth until the calf is weaned, during which time the calf frequently nurses on the mother’s nutrient rich milk. Baleen whales will wean their calves by their first summer when they are less than a year old, while toothed whales take up to three years to be completely weaned. Calves grow very rapidly, thanks to the extremely high proportion of fat and proteins contained in whale milk
The adult whale stage starts when the whale reaches sexual maturity. This can occur between the ages of six and 13 years, varying dramatically depending on the species.
Breeding often takes place seasonally in migrating species but in others it seems to occur through most of the year. In the adult stage, whales of both genders start searching for mates with whom to breed.
Sexually mature whales migrate to warmer waters during winter to mate. This ensures that when they return the next year, their calves will be born in more temperate conditions. Mating takes place every two to three years for the cow as her gestation period lasts for between 10 and 14 months.