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Canadian Amphibian and Reptile Conservation Network - Réseau Canadien de 
Conservation des Amphibiens et des Reptiles

Rana pretiosa
Oregon Spotted Frog / Grenouille maculée de l'Oregon


Oregon Spotted Frog

Description
The Oregon Spotted Frog is a large brown true frog with ill defined spots which may have light centres. It has dorsolateral ridges and a dark mask with a light stripe on the upper jaw. Its toes are fully webbed and the eyes are slightly upturned. The tympanum is prominent. The underside may be yellow, orange or red with dark mottling on the throat. Maximum adult size is 10 cm. The two species of Spotted Frogs are very similar and very closely related. It has only recently been recognized that they are two different species. The Oregon Spotted Frog differs from the Columbia Spotted Frog in having a smaller head.

Call
The call is a series of short, rapid grunts which build in intensity. The entire call may last up to ten seconds. It is not known if the call differs between the two species.

Confusing Species
The Spotted Frogs may be confused with Northern Red-legged Frogs which differ in having incomplete webbing on the toes and not having upturned eyes. Northern Red-legged Frogs do not have mottling on the throat and are always yellow beneath with red wash on the underside of the legs and the belly. Northern Leopard Frogs have much more distinct dark spots with light rings around them. The other true frogs found within its range do not have spots.

Distribution
The Oregon Spotted Frog is restricted to extreme southwestern British Columbia, adjacent areas of Washington and parts of Oregon and northern California.

Habitat
Spotted Frogs are found in permanent water in alpine and subalpine areas with mixed coniferous or subalpine forests.

Reproduction
Breeding occurs early in spring and egg masses are laid communally with each consisting of 700-1,500 eggs. They hatch in about four days. Larvae may transform by the end of summer or overwinter as tadpoles and transform the following year. They may take up to six years to reach maturity.

Natural History
Spotted Frogs are primarily aquatic and when frightened will swim to the bottom and remain still. Differences in natural history between the two species have not been explored.

Conservation Concerns
The Oregon Spotted Frog is very rare in British Columbia. The original known population appears to be extirpated but a new population was recently discovered.