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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Oregon Spotted Frog
Rana pretiosa
Family: Ranidae
COSEWIC status:- Endangered
- Endangered
- Vulnerable
Description
he Oregon Spotted Frog is a relatively large frog that can attain a body length of up to 10 cm, with males being smaller than females. Individuals are olive-green or brown as juveniles, but become reddish brown to red as adults, and they have distinct light-centred dark spots on the back. The underside is white to cream-coloured in juveniles and becomes orange or red with dark mottling in adults. Individuals have smooth skin with small bumps, upward-angled eyes, dorsolateral folds (folds of skin running down each side of the back) that often break up part way down the back, and extensive webbing that reaches the tips of the toes on the hind feet. Larvae (tadpoles) have long tails with a large tail fin and lack front legs (newly hatched tadpoles are legless). Larvae have a tan, dark brown or greenish body and tail with metallic flecking, dark spots or flecking on the tail fin, and a white belly. The larvae can reach 7–9 cm in length before metamorphosis. The call of the Oregon Spotted Frog is a rapid serious of short, low-pitched clucks of increasing intensity, which is said to sound like the distant tapping of a woodpecker.
Similar Species
The Oregon Spotted Frog may be confused with the Columbia Spotted Frog and the Northern Red-legged Frog. The Northern Red-legged Frog has semi-translucent skin on the underside of the hind legs, lacks the upward-angled eyes, and the webbing on the hind feet does not extend to the tips of the toes. The distributions of the Oregon and Columbia Spotted Frogs do not overlap, so these very similar species can be differentiated based on location.
Distribution
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The Oregon Spotted Frog has a very small Canadian distribution that is restricted to the Lower Fraser River Valley in southwestern British Columbia. This species has a patchy distribution in the United States, where it occurs at a small number of sites in western Washington and western Oregon. It is extirpated from California.
Habitat
Oregon Spotted Frogs inhabit and breed in large wetlands with shallow, warm areas and abundant floating or emergent vegetation. Inhabited wetlands are typically in forested areas, though Oregon Spotted Frogs are highly aquatic and rarely venture into terrestrial habitats. Individuals hibernate underwater in deeper parts of the occupied wetland.
Biology
In Canada, Oregon Spotted Frogs hibernate during the winter and are active from late February or March until October or November. Male Oregon Spotted Frogs call to attract females during the breeding season, which occurs in the early spring, immediately after ice recedes from the wetlands. During breeding, the male grasps the female (amplexus) and fertilization occurs externally in aquatic habitats as the female lays eggs. The female lays 250–1,000 eggs as a large gelatinous mass that is free floating in shallow water and not attached to aquatic vegetation. The eggs are black on top and white underneath and are surrounded by two clear jelly envelopes. The eggs hatch in 2–4 weeks and larvae transform into frogs 3–4 months after hatching. In Canada, individuals typically reach maturity at 3 years of age and may live for over 10 years. Individuals eat a wide variety of invertebrates, including spiders, beetles, aphids, mosquitoes, leafhoppers and slugs, as well as tadpole and juvenile frogs.
Threats
Oregon Spotted Frogs occur in one of the most developed regions in Canada, and the conversion of natural areas into urban and agricultural land uses has resulted in significant and ongoing declines of this species. Road mortality does not appear to be an issue for this species, likely because individuals rarely venture into terrestrial areas. Introduced invasive species, particularly the American Bullfrog, have also contributed to declines across much of this species’ range. Oregon Spotted Frogs are vulnerable to pollutants that can accumulate in wetlands, such as pesticides/herbicides, road salt, and industrial contamination. These environmental pollutants can be detrimental to Oregon Spotted Frog populations by causing direct mortality as well as developmental deformities. Pathogens, such as chytrid fungus and Ranavirus, can cause mass mortality of frog and toad populations. Climate change may also pose future threats to Canada’s frog and toad populations.