There are several endangered species in Sequoia National Park. The Big Horn sheep is one of the main species protected my the park. An additional 13 species, such as the wolverine, Sierra Nevada red fox, and Black-Tailed Hare are also endangered species in the park. Commonly observed species include yellow-bellied marmots, mule deer, Pika, and several species of squirrels, such as California ground squirrels, Douglas squirrels, golden-mantled ground squirrels, and Western gray squirrels. Most mammals in the park are nocturnal and they are rarely seen by park visitors. Some examples include Ring tailed-spotted skunks, short-tailed weasels, and mountain lions. Most of the mammals in these parks are secure, but there are some that are threatened with decline or even extinction. Once numbering over 1,000 animals throughout the Sierra Nevada, the federally endangered Sierra Nevada bighorn sheep was granted protection under the Endangered Species Act in 1999, when only about 125 individuals were left. Since then, the population has increased to about 400 individuals, but it is still threatened by the risk of disease from domestic sheep, predication by mountain lions, forest succession, genetic diversity, severe weather, climate change, and reduced geographic distribution.