ANWR is a biologically rich and diverse ecosystem, containing many important species of mammals. Of particular interest due to the conflict over its designation as a potential site for oil drilling, the coastal plain (also known as the 1002 area) is an area of critical importance. According to the United States Fish and Wildlife Service, there are as many as 130,000 Porcupine caribou that migrate more than 700 miles from their southern winter territory to their calving grounds on the coastal plain. These caribou rely on this coastal area for food and relief from predators in addition to a site for reproduction. This makes their annual migration an essential part of their life history. The remote nature of ANWR and absence of people, make it an ideal breeding grown, as calving caribou are sensitive to humans.
Like caribou, female polar bears rely on the coastal regions of ANWR for bearing cubs. Also, other mammals including a small population of muskoxen live in ANWR. Reintroduced in 1969 after having been nearly decimated by hunters in the 19th century, these animals live year round on the coastal plain. For at least part of the year, the coastal plain of ANWR is also home to such diverse species as wolves, moose, wolverines, snow geese, tundra swans, and peregrine falcons.