The Sierra Nevada red fox is to be listed as an endangered species following a decision by the U.S. Fish and Wildlife Service on Tuesday. The slender, bushy-tailed fox is one of the rarest mammals in the U.S., and its population has been threatened since the 1970s. According to the federal wildlife officials, the population of the red foxes has dropped to just 40 in an area stretching from Lake Tahoe to the south of Yosemite National Park in California. The U.S.