Western American Subregion

a subregion of the Nearctic division of the zoogeographic Holarctic region. The subregion occupies the western part of North America (west of the 100th meridian and south of the Circumboreal subregion). The Western American subregion differs from the Eastern American in having prairies and deserts. The unique fauna and substantial number of endemics are due to the deserts and mountains, as well as to some historical factors. The resemblance to the Palearctic division is greater in this subregion than in the Eastern. Mammals include four endemic families: mountain beavers, gophers (burrowing ro-dents), kangaroo rats, and pronghorn antelope. This is the only area in the New World inhabited by pikas. The grizzly bear, American bison (almost extinct), mountain sheep, Rocky-Mountain goat, leaf-nosed bat (of southern origin), coat, and cacomistle (a small predator) are characteristic. There are some endemic species; including ground squirrels and polecats. There are few endemic genera among the birds. Hummingbirds (six species), California condor, and others impart a unique character to the fauna; the sage grouse and some quail are endemic. There is a substantial number of reptiles, with lizards predominant (in contrast to the Eastern American subregion, where snakes and turtles are predominant). The iguana family is well represented, including the moloch, a desert lizard; the anguine lizard is characteristic. The families of legless, burrowing lizards, the Annillidae and Helodermatidae (which consist of two species, the only poisonous lizards on earth), are endemic, as are some species of the families Gekkonidae and Amphisbaenidae. The amphibian fauna is poorer than in the Eastern subregion. There are few freshwater fishes. Migratory salmon are predominant in the northern part.