Sea Cows Dugongs and Manatees: Sirenia

Sirenians are semi-social mammals with the primary unit a female and her calf. Dugongs feed in herds of tens or hundreds of individuals. They have been recorded as traveling hundreds of miles (kilometers) in a matter of days, an impressive feat given that they must surface for air every few minutes. Dugongs have poor eyesight but an acute sense of hearing.

Manatees also travel long distances in short amounts of time and have a north-south migratory pattern, the direction or path taken during seasonal movement from one region to another, that keeps them swimming in warmer waters. Although most marine mammals use echolocation (eck-oh-loh-KAY-shun), a sensory system in which high-pitched sounds are used to determine location and distance, sirenians are not known to. Little is known about the behavior of Steller's sea cow.

Manatees reach sexual maturity between the ages of two and eleven years. Gestation, pregnancy, is believed to be twelve or thirteen months. Usually a single calf is born every two-and-a-half to three years. Manatees do not bond, which means they have numerous mates throughout their lifetimes. In fact, when a female is ready to breed, she may mate with as many as twenty males, often at the same time. Calves can swim to the surface at birth, and they are nursed, fed with mother's milk, until around the age of one. Though they have no vocal cords, calves also vocalize at birth, which is an important part of the mother-calf bonding process. The calf remains close to its mother for up to two years.

Pregnancy for the dugong lasts about one year and results in the birth of a single calf, which will nurse from and remain close to its mother for about eighteen to twenty-four months. Birth takes place in shallow water and the calf will rise to the surface to take its first breath. Dugong calves are about 3.3 to 3.9 feet (1 to 1.2 meters) and weigh 44.1 to 66.2 pounds (20 to 30 kilograms). Dugongs can live for seventy years.

Because Steller's sea cow died out so quickly, most of what we know is speculation, an educated guess based on facts. Gestation lasted at least one year, and calves were seen throughout the year, suggesting that there was no specific breeding season. Pregnancy resulted in single births, but physical data is not available. It is believed that the sea cow was monogamous (muh-NAH-guh-mus), having only one mate.