Reproducing

How do whales mate? Like other mammals, such as humans, male whales (called “bulls”) have a penis and females (called “cows”) have a vagina. They mate underwater, usually belly to belly, while either stationary or swimming.

In many species, males usually mate with more than one female, and females with more than one male. After giving birth to a baby (called a “calf”), a female will generally nurse the calf for six months an then rest for six months before attempting to mate again.

Like most other large animals, whales have a low birth rate. On average, they become sexually mature around 8-10 years old, and a cow may give birth to one calf every few years. Humpback whale calves take about 11 months to develop in the womb, but sperm whales gestate for 15 months.

The calf is born tail first—and ready to swim! This is essential, as it has to get to the surface to breathe. The newborn calf is already well developed—it may be as much as a third of the length of the mother.

Mothers generally nurse their calf for about six months, and for much longer in strongly social species (up to two years for sperm whales.) Weaning is a gradual process, with the young animal starting on solid food before it has finished with its mother’s milk—just as humans do.