The word narwhal means "corpse whale" in Old Norse, the actual whale is rarely seen. Therefore, very little is known about this whale. All narwhals have two teeth in their upper jaw. After the first year of a male narwhal's life, its left tooth grows outward, spirally. The long, single tooth projects from its upper jaw and can grow to be seven to ten feet long. Tusks are usually twisted in a counterclockwise direction and have a hollow interior. The tusk's function is uncertain, perhaps used as a formidable jousting weapon in courtship and dominance rivalry, in obtaining food, and/or channeling and amplifying sonar pulses. The tusk is not used in hunting. Long ago, narwhal sightings reinforced the unicorn legends. Narwhals can grow to be about sixteen feet long (not counting the tooth) and weigh about 1.8 tons. Females are slightly smaller averaging about thirteen feet in length and weighing in at one ton. At birth, narwhals are about five feet log and one hundred and seventy five pounds. The skin on this animal is bluish-gray with white blotches (young narwhals are brown). Narwhals have a cylindrical body (with no dorsal fin) and a round head with a small mouth on their blunt snout. This compact body shape plus a thick layer of blubber retains heat in the icy Arctic water in which they live. They rarely stray far from the ice, in the summer they infrequently enter estruaries and bays. The duration of this mammals dive is from seven to twenty minuts. Narwhals are also a very vocal species of whale, making clicks, sqeauls, and whistles to communicate and/or navigate. They are though to live a maximum of about fifty years, and eat fish, squid, shrimp, and other marine mammals. Pods of four to twenty narwhals have been observed, some consist of just one sex and others contain both sexes. Many pods may travel together, forming very large groups. It is estimated that there are roughly ten thousand to fourty five thousand narwhals. The narwhals gestation period is ten to sixteen months. Calves are brown and have no spots, they are nursed for about four months after birth.