Spotted Frog

Last Review/Updated: May 30, 2002

Rana pretiosa

Description

The spotted frog ranges from 45-100 mm in length and is covered with small dark spots. It is generally a dark brown with a pink or red underside. The dorsolateral folds are present but somewhat indistinct. The frog may have a "mask" covering the eyes and snout like the wood frog, but the spotted frog is much larger. Although it is about the same size as the northern leopard frog, the spotted frog lacks the light-coloured dorsolateral folds. In addition, spotted frogs tend to have smaller spots and they lack the light rings circling the spots.

Natural History

This frog is generally aquatic and is found near permanent bodies of cold water such as streams or marshes in relatively mountainous areas. Despite living in alpine environments, it is basically nocturnal. Prey items include insects, worms, and crustaceans. The spotted frog is currently on the Blue List in the Status of Alberta Wildlife and is considered to be at risk, or vulnerable.

Breeding

Because of their high elevation locations, spotted frogs breed later than some other frogs. Breeding can be as late as May or June, depending upon snowmelt. Males emit quick, low-pitched calls, which sound vaguely like a helicopter. Females lay large eggs (5-8 mm in diameter) in communal masses. Each female can lay up to about 1500 eggs, which will hatch in about four days.

Larvae

The tadpoles are dark brown or dark green and are speckled with gold. Depending upon water temperature and the length of the summer season, the tadpoles will either transform late in the summer or overwinter as tadpoles. The newly transformed frogs are about 25 mm long. It can take up to 4-6 years for them to reach sexual maturity.

Distribution

The spotted frog is limited to the mountainous areas of Alberta. It is found in alpine and subalpine regions up to elevations of just over 2000 m. It is widely distributed throughout most of B.C. and even occurs in southern Alaska.

Monitoring

Spotted frogs are primarily nocturnal, making them difficult to locate outside of the breeding season. In the spring, adults will congregate at breeding ponds and begin calling.