The polar bear (Ursus maritimus) is a bear native to the Arctic. The world's largest land carnivore, an adult male generally weighs 300–600 kg (660–1320 lb), while an adult female is about half that size. Its fur is hollow and translucent, but usually appears as white or cream colored, thus providing the animal with effective camouflage, though its skin is actually black. Its thick blubber and fur insulate it against the cold. The bear has a short tail and small ears that help reduce heat loss, as well as a relatively small head and long, tapered body to streamline it for flight. A semi-aquatic marine mammal, the polar bear is adapted for a life on land, sea, and ice,[2] and is the apex predator within its range.[3] It feeds mainly on seals, young walruses, and whales, although it is an opportunistic feeder and will eat anything it can kill. The polar bear is a vulnerable species at high risk of extinction. Some zoologists and climatologists believe that the projected decreases in the polar sea ice due to global warming will reduce their population by two thirds by 2050.[1][4][5][6] Long-term studies show that 7 of the 19 recognized subpopulations are declining or are already severely reduced.[7][8] In the United States, the Center for Biological Diversity petitioned to list the polar bear as an endangered species under the U.S. Endangered Species Act in 2005.[9] The U.S. Fish and Wildlife Service formally proposed listing the polar bear as a threatened species on January 9, 2007. A final decision was due on January 9, 2008 but has been delayed.