Bottlenose dolphin females typically become sexually mature at 5 to 13 years of age. Their reproductive lifespan is prolonged. Dolphin females, up to 48 years of age, have successfully given birth and raised young.
Males mature later, at about 9 to 14 years of age. Paternity testing of calves has shown that their fathers ranged in age from 13 to 40 years. Some males are far more successful at becoming fathers than others.
Calves are born in all seasons, but most are born in the spring and summer. The gestation period is about one year. At birth, calves measure about a meter (3.8 feet) long and weigh about 18 kilograms (40 pounds).
Calves usually stay with their mothers for 3-6 years. During this time the calves must learn how to catch their prey, how to avoid dangers, and how to find their way around the home range. They also become integrated socially into the dolphin community.
Calves usually separate from their mothers and join juvenile groups when the mother’s next calf is born. Older calves still may sometimes be seen swimming with their mom and the new sibling.
Older female calves will usually return to be a member of the mother’s female band. These bands might include 4-5 generations of relatives. While band members may use similar home ranges, they are not always swimming together.
Associations between females are based mostly on their reproductive condition. Moms with calves of similar age often swim together, and pregnant females often swim together.
Male calves will usually pair up form a male alliance.
Calves nurse under water, which becomes an intricate ballet. The calf usually must dive to find the mother’s mammary slits, located about two-thirds of the way down her belly.
The calf prods the mammary slit, which causes a milk gland to shoot milk into the calf’s mouth. The calf rolls its tongue to channel the milk. Nursing only lasts a few seconds, and so must be repeated frequently.
Calves usually nurse for several years, and they begin to eat a few little fish when they are as young as a few months old. Over a period of years, calves learn to catch fish on their own, and they decrease consumption of their mother’s milk.
Relevant SRRP citations
Urian, K.W., D.A. Duffield, A.J. Read, R.S. Wells and D.D. Shell. 1996. Seasonality of reproduction in bottlenose dolphins, Tursiops truncatus. J. Mammalogy. 77:394-403.
Wells, R.S. and M.D. Scott. 1999. Bottlenose dolphin Tursiops truncatus (Montagu, 1821). Pp. 137-182 In: S.H. Ridgway and R. Harrison (eds.), Handbook of Marine Mammals, Vol. 6, the Second Book of Dolphins and Porpoises. Academic Press, San Diego, CA. 486 pp.
Wells, R.S. 2003. Dolphin social complexity: Lessons from long-term study and life history. Pp. 32-56 In: F.B.M. de Waal and P.L. Tyack, eds., Animal Social Complexity: Intelligence, Culture, and Individualized Societies. Harvard University Press, Cambridge, MA.
All photos © Sarasota Dolphin Research Program under NMFS permit #522-1785