The Sagebrush Sea supports an estimated 250 terrestrial vertebrate species, including 100 bird and 70 mammal species. The Snake River Birds of Prey National Conservation Area south of Boise, Idaho, hosts the largest population of nesting raptors in North America (approximately 700 pairs of raptors representing 15 species). Increasingly rare big sagebrush habitat is alive with 94 bird species, 87 mammals, 72 spiders, 58 reptiles, 52 aphids, 32 gall midges, 31 fungi, 24 lichens, 23 ants and 23 beetles. Black-tailed jack rabbits are the most abundant large herbivore in the Sagebrush Sea; populations oscillate from approximately 60 to 600 rabbits per square kilometer. Black-tailed jack rabbits have increased and white-tailed jack rabbits have declined in sagebrush steppe as shrubs have increased (due to livestock grazing) relative to grasses and forbs. Coyotes are a top-level predator in the Sagebrush Sea and a very effective predator of jack rabbits.
Pinyon and juniper species occur in the Sagebrush Sea and individual trees may live for hundreds of years. The oldest living tree in Oregon is a western juniper that is over 1,600 years old. Bristlecone pines more than 4,000 years old have been found at the highest elevations in the Sagebrush Sea.
Science has identified at least 163 species and subspecies of aquatic fauna endemic to Great Basin rivers, lakes, streams, and cold and hot springs (67 fishes, 85 mollusks, 9 insects, 2 amphibians, 1 fairy shrimp). Great Basin wetlands support 61 aquatic bugs, 19 endemic plant species and 5 endemic plant varieties, and 4 endemic vole subspecies.
More than 1,000 different insects and invertebrate species may be found in sagebrush steppe (more than 1,240 insects have been identified at the Idaho National Laboratory in eastern Idaho). Their impact on ecosystem dynamics is marked: harvester ants were observed moving vast quantities of leaves and seeds underground in sagebrush steppe near Reno, Nevada-between 63 and 92 million annual plants per acre annually.
Sagebrush obligate species (wildlife that depend on sagebrush habitats during the breeding season or year-round) include greater sage-grouse, Gunnison sage-grouse, sage sparrow, Brewer's sparrow, sage thrasher, pygmy rabbit, sagebrush vole, sagebrush lizard, and pronghorn. As many as 16 million sage-grouse may have occurred in sagebrush steppe prior to European arrival.
The use and abuse of the Sagebrush Sea—the draining and diversion of its streams and wetlands, conversion of sagebrush and native grasses to cropland and exotic forage plants, invasion by weeds and other non-native species, a century or more of intensive livestock grazing, energy development, and unnatural fire—have eliminated and degraded large ares of the landscape. If current land uses continue without modification, the future of many Sagebrush Sea species will be uncertain.