Twelve amphibian and 22 reptile species inhabit Yosemite National Park. They are often considered together because both are poikilotherms, animals that lack the ability to generate their own body heat, relying instead on their environment to regulate body temperature. Amphibians spend the early part their life cycle in water as larva before metamorphosing into adults that live on land. Toads are a good example. As tadpoles, they are restricted to aquatic environments, but spend almost all of their time on land as adults. In contrast, reptiles are generally terrestrial throughout their life cycle. Amphibians are also characterized by moist, highly vascularized skin while reptiles are typically covered by scales.
Yosemite's amphibians can be divided into two groups - anurans and caudates . Anurans are frogs and toads. Caudates include newts and salamanders. They have tails and resemble lizards in appearance. Caudate amphibians spend most of the year hidden to escape Yosemite's hot dry summers. They live under rocks and rotten logs or underground in damp crevices and burrows and typically emerge in autumn after the first soaking rain. Yosemite's lone newt species, the California newt, is the park's most visible caudate. They move like a lizard in slow motion and are often observed in early spring crossing roads or trails on their way to breed in rivers and streams. Of the four salamander species inhabiting Yosemite, one, the Lyell salamander, is endemic to the region.
Yosemite's anurans include the western toad; its close relative, the Yosemite toad; and five species of frogs. The Yosemite toad is endemic to the region. The most common frog species is the ubiquitous Pacific treefrog. Found at nearly all elevations in nearly all habitats, this diminutive frog is the species most often heard calling around meadows and ponds in the spring. The bullfrog is an non-native introduced species restricted to a few locations in Yosemite Valley and near Hetch Hetchy. The other three frog species are the red-legged frog, the foothill yellow-legged frog, and its cousin, the mountain yellow-legged frog. Yosemite has very little suitable habitat for the red-legged and foothill yellow-legged frog, thus these species are extremely rare within the park and may be extinct. Because they have also disappeared from many other locations around California, red-legged and foothill yellow-legged frogs are being considered for endangered species status. Mountain yellow-legged frogs have been rapidly disappearing in Yosemite. Predation by non-native fish is the major cause.
The mountain yellow-legged frog inhabits higher elevations and was once numerous in Yosemite's lakes and streams. However, in recent years, its numbers have declined dramatically and it is also being considered for protection under the Endangered Species Act. The cause of this frog's disappearance, and that of both toad species, is currently uncertain. Evidence strongly suggests that trout, introduced to Yosemite's lakes and streams, have played a role in amphibian population declines. Pesticides drifting into the park from California's Central Valley and diseases have also been implicated.
In marked contrast to the amphibian's preference for moist, damp habitats, reptiles prefer dry, rocky places. Yosemite's reptile fauna can be divided into three groups - turtles, lizards, and snakes. The lone turtle species, the western pond turtle, is an uncommon resident of mid-elevation ponds and slow moving streams. The eight lizard and thirteen snake species are seen at varying degrees of frequency.
The western fence lizard is the most numerous and readily observed lizard species in Yosemite. They are often seen darting across granite slabs or heard skittering through dry leaves. They are easily recognizable as the lizard doing "pushups," a common display behavior. The northern and southern alligator lizards are almost as common as the western fence lizard. However, their habit of hiding under rocks and logs makes them much less obvious. The coast horned lizard is extremely rare and has only been recorded once or twice within the park.
Yosemite has a diverse snake fauna with thirteen species recorded in the park. The most common are the garter snakes with three species. They frequent ponds and wet meadows hunting for small fish and frogs. The mountain king snake with red, black, and cream colored bands encircling its body is the park's most beautiful snake. The rubber boa looks like a giant earthworm. Light gray in color with a blunt tail, this gentle snake primarily eats insects and soil invertebrates. The remaining species are uncommon to rare, mainly inhabiting the warm, dry lower elevations of the park.
Of the thirteen species of snakes found in Yosemite, only the western rattlesnake is venomous. Fortunately, the likelihood of encountering one is relatively low. Pay attention when hiking or climbing in dry, rocky places. Avoid putting your hands in holes or on ledges where snakes may be sunning themselves. If you do see or hear one, simply detour around it or let the snake crawl away. Rattlesnakes are an important part of Yosemite's ecosystem, as they help keep the park's rodent numbers in check.
With the exception of the mountain yellow-legged frog and Yosemite toad, relatively little is known about the amphibian and reptile fauna of the park. Ongoing investigations into the causes behind declining frog and toad populations are our best source of information.