Births take place during the early spring through late summer of the Southern Hemisphere, October through March.

Just one calf is born at a time. Calves are born in the water, usually tail first.

A newborn Commerson's is about 55 to 65 cm (21.7-25.6 in.) in length and weighs 4.5 to 5.5 kg (10-12 lb.). This heavy calf makes up about 22% of the mother's body weight and is about 61% her length.

In the first few days after birth, the dorsal fin and tail flukes are flexible and pliable. They gradually stiffen.

The calf is gray at birth. Its' skin shows several vertical light lines, a result of fetal folding. These folds disappear in about a week.

A whale calf suckles from nipples concealed in abdominal mammary slits.

Calves nurse below water, close to the surface.

The mother's rich milk helps the baby rapidly develop a thick blubber layer.

Calves grow quickly. In the first year of birth, calves average 92 to 112 cm (36-44 in.). One-year-old calves are about 99 to 117 cm. (39-46 in.). Compare this to the average adult length of 120 to 170 cm (47-67 in.) and you'll see that a large one-year-old can be virtually the same size as a small adult.

The first Commerson's dolphin born in a marine zoological park was born at SeaWorld San Diego on February 22, 1985.