Yosemite is home to 90 species of mammals in seven orders, including marsupials, insectivores, bats, lagomorphs, rodents, carnivores and hooved animals. The Virginia opossum is the lone marsupial. Seven species of shrews and one mole comprise insectivores. Lagomorphs include one rabbit, the pika, and three hares. Bats and carnivores number 17 and 19 species, respectively. Rodents form the largest group with 39 species. The two hooved mammals inhabiting the park are the California mule deer and the Sierra Nevada bighorn sheep. One species, the Mount Lyell shrew is endemic to the Yosemite region while two others, the Virginia opossum and beaver are non-native introductions.
The Order Rodentia includes many common genera. Mice, chipmunks, squirrels, and gophers are its best known members. The order also includes lesser known taxa like voles. Mice and their allies (8 species), chipmunks (8 species), and squirrels (6 species) constitute more than half of the rodent species in the park. Most of the remaining genera are represented by only a single species like marmots, aplodontia, and porcupines. The fisher is a highly effective predator, equally at home on the ground and in the trees.
Carnivores are perhaps the most widely recognized group of mammals in Yosemite. Its members include the American black bear, bobcat, mountain lion, raccoon, coyote, foxes, weasels, and skunks. Lesser known species like the American marten, fisher, and ringtail are also present. Although grizzly bears once roamed the area, they were extirpated from Yosemite when the last individual was shot in the early 1920's.
Although often overlooked because of their nocturnal habits, bats represent a large proportion of the park's mammalian fauna. The mobility of these remarkable flying mammals enables them to occupy a wide range of habitats. They are found from the lowest elevations in the park to over 10,000 feet. They roost in rock crevices and caves, under loose bark and bridges, in attics and tree cavities. North America's largest bat species, the western mastiff, is a Yosemite resident, as is the spotted bat with its huge ears and vivid white spots. These are the only two species in Yosemite whose echolocation calls are audible to the human ear.
Many of Yosemite's mammals, like mule deer and gray squirrels, are fairly common and can be readily seen every day. Others, like the wolverine and Sierra Nevada red fox, are extremely rare and might be sighted only once a decade. Of the 90 mammal species on the park's fauna list, 17 are considered "special status" by either the federal or California state government due to declining population numbers or a lack of information about their distribution and abundance. Currently, Sierra Nevada bighorn sheep are the only park mammal on the U.S. Fish and Wildlife Service Endangered Species list.
Several mammal species have been the subject of research within the park. Graber (1980) investigated black bear ecology and population dynamics. Sherman and Holmes (1985) conducted long term studies of belding ground squirrel social behavior. Todd (1990) examined the distribution, abundance and habitat requirements of Sierra mountain beaver. And Chow (1991) studied the population dynamics and movement patterns of Sierra Nevada bighorn sheep while Moore (1992) examined the foraging ecology of those sheep. Additional work on forest carnivores and the interactions between mountain lions and human beings is also in progress.