If twins are conceived, they are unlikely to survive to full term. In rare cases where twins are born, they are not likely to survive, due to a limited milk supply from the mother. In most species, females may bear a calf every two to four years. Observations of baleen whale births at sea are extremely rare. The placenta seperates from the uterine wall during or soon after delivery.
Some species seek protected coastal areas to give birth.
E. Calf at birth. Calves can swim at birth. In general, a calf is approximately one-quarter of the mother's length. Baleen whale calves have small, soft baleen plates. See also baleen.