What Does a Narwhal Use Its Horn For?

A variety of theories have been proposed for the specific function of the narwhal’s long, straight tusk, but first we have to point out that it’s not a horn. You can be forgiven for thinking it’s a horn, especially since the narwhal’s tusk is grooved in a left-handed spiral, resembling traditional depictions of the imaginary unicorn’s horn. Indeed, during the Middle Ages narwhals were hunted in the arctic waters of northern Europe, and their tusks were then sold as unicorn horns to wealthy clients who had probably never seen a narwhal. But the unicorn of the sea does not have a horn. Horns typically come in pairs and grow from the upper portion of the head of hoofed mammals, such as sheep or antelopes. They often serve as weapons of defense against predators and of offense in battles between males for breeding access to females.

A narwhal has a tusk, which is actually an overgrown tooth just like the tusks of elephants or walruses. Narwhals have only two teeth, both at the tip of the upper jaw, not inside the mouth—they swallow fish whole. Usually, only the left tooth develops, and the resulting tusk grows to more than 3 meters (9.8 feet). The undeveloped right tooth in males and usually both teeth in females remain vestigial. However, though females usually don’t have even one tusk, on rare occasions two tusks may develop in females as well as males. Narwhals, which can live up to 125 years, sometimes lose their tusks over time.

So now we can go back to the question about what this overgrown tooth does. Recent observations by scientists suggest that narwhals use their tusks to hunt fish, shrimp, or squid and to detect the level of salt in the waters. In hunting, narwhals use their tusk not to spear their prey but rather to give it a quick firm tap that momentarily stuns the target. The narwhal then slurps up the creature whole.

The exterior of the narwhal tusk is very sensitive, having up to 10 million nerve endings, and this helps narwhals ascertain the level of salt in the Arctic waters through which they swim. Higher salinity can indicate colder water because salt is left behind as ocean water freezes. It’s possible that a narwhal’s tusk is used to help it navigate away from more frigid areas.

Previously, researchers, including English naturalist Charles Darwin, believed that narwhals use their tusks in the way hoofed animals use their horns, in aggression against one another in competition for mates. This theory was supported by the presence of tusk scars on male narwhals, indicating that they might use their tusks to establish dominance. However, this aggressive use of the tusk is now considered less significant compared with its sensory and hunting functions. The tusk may still play a role in social interactions, possibly serving as a display feature to attract mates or establish social hierarchy within groups.