Yellowstone is widely considered to be the finest megafauna wildlife habitat in the lower 48 states. There are almost 60 species of mammals in the park, including the gray wolf, the threatened lynx, and grizzly bears. Other large mammals include the bison (buffalo), black bear, elk, moose, mule deer, white-tailed deer, mountain goat, pronghorn, bighorn sheep and mountain lion.[1]

Bison

Bison once numbered between 30 and 60 million throughout North America; Yellowstone is one of their last strongholds. Their populations had increased from less than 50 in the park in 1902 to 4,000 by 2003.

The park's bison population reached a peak in 2005 with 4,900 animals. Despite a summer estimated population of 4,700 in 2007, the number dropped to 3,000 in 2008 after a harsh winter and controversial brucellosis management sending hundreds to slaughter.[5] APHIS has stated that with vaccinations and other means, brucellosis can be eliminated from the bison and elk herds throughout Yellowstone.[6]

Wolves

Starting in 1914, the U.S. Congress gave funds for the purposes of "destroying wolves, prairie dogs, and other animals injurious to agriculture and animal husbandry" on public lands. After the wolves were gone from Yellowstone, the coyote became the park's top canine predator. However, the coyote cannot bring down large animals. The result was a great increase in lame and sick megafauna.

By the 1990s, the Federal government had reversed its views on wolves. In a controversial decision by the U.S. Fish and Wildlife Service, wolves, imported from Canada, were reintroduced into the park. A survey conducted in 2005 showed there were 13 wolf packs, totaling 118 individuals in Yellowstone and 326 in the whole ecosystem.

The recovery of populations throughout the states of Wyoming, Montana and Idaho has been so successful that they are no longer on the endangered species list.[7]

Beruang

Kira-kira 600 ekor beruang grizzly hidup di Ekosistem Yellowstone Raya, dengan lebih daripada separuh berada di dalam Yellowstone.[8]

Elk

Jumlah populasi elk lebih daripada 30,000. Ia merupakan populasi spesies mamalia terbesar Yellowstone. Jumlah kawanan di utara menurun dengan mendadak sejak pertengahan tahun 1990-an. Ini mungkin di sebabkan oleh serigala. Selain itu, elk lebih banyak menggunakan kawasan berhutan bagi mengelakkan serigala, dan menjadikan keadaan lebih sukar bagi para penyelidik untuk mengira jumlahnya.[9] Pada musim sejuk, kawanan utara berpindah ke barat ke arah barat daya Montana. Kawanan selatan pula menuju ke arah selatan. Perpindahan kawanan selatan merupakan migrasi mamalia terbesar yang masih wujud di luar Alaska, Amerika Syarikat.

Other predators

In 2003, the tracks of one female lynx and her cub were spotted and followed for over 2 batu (3.2 kilometer). Fecal material and other evidence obtained were tested and confirmed to be those of a lynx. No visual confirmation was made, however. Lynx have not been seen in Yellowstone since 1998, though DNA taken from hair samples showed that lynx were at least passing through the park.[10] Other less commonly seen mammals include the mountain lion and wolverine. The mountain lion has about 25 individuals parkwide.[11] The wolverine is another rare park mammal, and accurate population figures for this species are not known.[12]

Yellowstone is also home to six species of reptiles, such as the painted turtle and Prairie rattlesnake, and four species of amphibians, including the Boreal Chorus Frog.[13]

Ikan

Lapan belas spesies ikan hidup di Yellowstone, termasuk trout cutthroat Yellowstone—sejenis ikan yang paling dikehendaki oleh pemancing.[1][14] Trout cutthroat Yellowstone menghadapi beberapa ancaman sejak tahun 1980-an, termasuk kemasukkan secara haram tasik trout ke dalam Tasik Yellowstone, sejenis spesies rempuhan yang memakan trout cutthroat yang lebih kecil.[15][16] Trout cutthroat juga menghadapi kemarau, selain kemasukkan tidak sengaja sejenis parasit—penyakit pusaran—yang mana membunuh anak-anak ikan. Sejak tahun 2001, kesemua spesies ikan sukan asli yang ditangkap di salur air Yellowstone tertakluk kepada undang-undang tangkap dan lepas.[14]

Burung

311 spesies burung telah dilaporkan, hampir separuh darinya membiak di Yellowstone.[1] Setakat tahun 1999, 26 pasang Helang Botak dilaporkan membuat sarang.