The Beluga or White Whale (Delphinapterus leucas) is an Arctic and sub-Arctic species of cetacean. It is one of two members of the family Monodontidae, along with the Narwhal. This marine mammal is commonly referred to simply as the Beluga or Sea Canary due to its high-pitched twitter. It is up to 5 m (15 ft) in length and an unmistakable all-white color with a distinctive protuberance on the head. From a conservation perspective, the Beluga is considered "near threatened" by the International Union for Conservation of Nature; however the sub-population from the Cook Inlet in Alaska is considered critically endangered and has been placed under the protection of the Endangered Species Act by the U.S. federal government.