Antelope Island State Park is the largest of the Great Salt Lake’s islands, encompassing 42 square miles of rangeland and mountainous terrain in northern Utah. Connected to the mainland by a seven-mile causeway, this environment functions as a protected refuge for free-roaming wildlife. The island’s isolation provides a memorable setting for observing a variety of species native to the Great Basin ecosystem. The park’s management focuses on preserving this landscape to support the diverse animal populations that thrive within its boundaries.
The Iconic Grazers: Bison and Pronghorn
The American Bison herd on Antelope Island is one of the nation’s oldest and largest publicly owned herds, originating from 12 animals introduced in 1893. The population is actively managed, typically fluctuating between 500 and 700 individuals, peaking after spring calving. To ensure genetic health and prevent overgrazing, park staff conduct an annual roundup in late October. During this event, horseback riders move the animals into corrals for vaccinations, medical checks, and selection for auction.
The island’s namesake, the Pronghorn, is another prominent grazer frequently seen across the landscape. These mammals are not true antelope but represent the sole surviving member of the Antilocapridae family. Pronghorns are the fastest land animals in North America, capable of reaching bursts of up to 60 miles per hour. Their large eyes and open-country habitat preference allow them to detect predators from a significant distance.
Terrestrial Mammals and Predators
The island’s rugged slopes and canyons provide habitat for other specialized mammals, notably the Rocky Mountain Bighorn Sheep. Although native to the area, the original population was lost in the early 1900s, necessitating reintroduction efforts. A new herd was established in 2020 following a disease outbreak that decimated the previous group, with a management goal of maintaining approximately 125 animals. The bighorn sheep are valued as a source population, with individuals periodically transplanted to augment other herds throughout Utah.
The primary predator on Antelope Island is the Coyote, which regulates populations of smaller prey animals. Coyotes are opportunistic hunters and scavengers, primarily feeding on voles, jackrabbits, and cottontails. The island also supports a population of Bobcat, an elusive feline recognizable by its short, “bobbed” tail. Mule Deer are also common terrestrial mammals, frequently seen browsing the island’s vegetation.
Birds and the Great Salt Lake Ecosystem
The Great Salt Lake surrounding the island supports millions of birds migrating along the Pacific Flyway. The lake’s high salinity limits aquatic diversity but creates an enormous abundance of two specialized invertebrates: Brine Shrimp and Brine Flies. These organisms form the critical food base that sustains the massive avian populations.
Millions of Eared Grebes and Wilson’s Phalaropes use the Great Salt Lake as a crucial staging area to molt and build energy reserves before migration. Up to 95% of the North American population of Eared Grebes can congregate here during the fall staging period. The island’s open skies are patrolled by various raptors, including year-round resident Golden Eagles. Visitors can also spot Northern Harriers, Red-tailed Hawks, and Bald Eagles during the winter months.
Tips for Viewing Wildlife Safely
Visitors should prioritize safety by maintaining a significant distance from all wildlife, especially the large bison herd. Park officials advise doubling any distance considered safe, as large animals can be unpredictable and aggressive if they feel threatened. Never attempt to approach bison or pronghorn for photographs; always use a telephoto lens or camera zoom for close-up images. If a bison is encountered on a trail, slowly retreat or leave the trail to give the animal a wide berth. The island’s scenic loop road and the area around the historic Fielding Garr Ranch are known locations for good sightings, with activity highest during the cooler hours of dawn and dusk.