Reproductive behavior is known mostly from studies on captive individuals,
primarily the bottle-nose dolphin. Copulation normally occurs during the spring
months, with the male-female pair exhibiting courtship for some time prior to
copulation. Gestation in the species studied is between 11 and 12 months, after
which a single calf is produced. Delivery is normally tail first, and the
newborn is capable of swimming and breathing within the first minutes. Some
mothers have been observed raising the calf to the surface, as if to help it,
but dolphins apparently play in this fashion with a variety of objects, living
or not. Such play may have provoked the stories of drowning persons being
helped to shore by dolphins.
After birth, the calf follows its mother closely, and suckling takes place
frequently, with the mother rolling slightly and the calf nuzzling the mammary
area. The dolphin's two mammary glands open into a pair of sacs on either side
of the anal opening, and the calf's beak fits into the openings of the sacs.
The nipple is grasped between the upper jaw and the tongue, and muscular
contractions by the mother literally squirt milk into the calf's mouth. Nursing
may continue for as long as 12 to 18 months after birth, although weaning is
probably slowed or inhibited in captive animals.