Ministry of Environment
Oregon Spotted Frog
|Common Name:||Oregon Spotted Frog|
|Scientific Name:||Rana pretiosa|
The Oregon Spotted Frog is a medium-sized frog with light-centred black spots on the head and back. Adult frogs are green, brown or reddish brown as adults, while juveniles are brown or olive green. Two dorsolateral folds, which are usually lighter in colour than the frog's body, appear as stripes part way along the back. The eyes are set so that when you look straight down on an Oregon Spotted Frog, it gives the appearance of looking straight back up at you. Adults can grow to a length of 5 to 10 centimetres from the snout to the rump.
Similar frogs in B.C. include the Columbia Spotted Frog and the Red-legged Frog. The Columbia Spotted Frog can only be distinguished from the Oregon Spotted Frog with considerable experience, and until very recently was considered the same species. The Columbia Spotted Frog lives in the interior of B.C., and is much more common than the Oregon Spotted Frog. Red-legged Frogs, whose range overlaps that of Oregon Spotted Frogs, have eyes that are angled outward, have flecks rather than spots and much brighter legs than Oregon Spotted Frogs.
When viewed from a distance, Oregon Spotted Frogs have a distinct posture on land - they crouch to the ground, rather than sitting up straight as Red-legged Frogs do. Oregon Spotted Frogs spend much of their time in the water and when disturbed will dive to the bottom and stay there for quite some time. This makes them very difficult to find.
Oregon Spotted Frogs live in floodplain wetlands associated with permanent water bodies and prefer the warm, shallow edge of marshes to lay their eggs. Transformed Oregon Spotted Frogs are mainly aquatic, and temporary ponds, like the ones that often form after spring rains, are also important habitat features. Unfortunately, these habitats are very vulnerable to fluctuating water levels, and changing land use patterns. Oregon Spotted Frogs prefer ponds that are exposed to sunlight, so that the water can be warmed; too much shade can make an area unsuitable for them.
Oregon Spotted Frogs are far more aquatic than other native frogs - they leave the water for very short periods when foraging, and never move between ponds except by connecting waterways. This makes the frogs especially vulnerable to fragmentation of their habitat.
Oregon Spotted Frogs gather in breeding ponds in early spring. Males make a low-pitched call that sounds like a series of soft knocks on wood to attract females. Females lay egg masses communally, or in groups, in shallow water. The tadpoles metamorphose into small froglets after about four months, and take two or three years to reach breeding age. Like most frogs, Oregon Spotted Frogs do not guard or feed their young. The lifespan of Oregon Spotted Frogs is unknown, but is probably not more than four or five years.
Adult Oregon Spotted Frogs eat mostly invertebrates such as beetles, flies, spiders, and water striders. They are "sit and wait" predators, remaining motionless in the water or on the shore, until something wanders by that looks tasty. The frogs then lunge toward the prey and capture it with a sticky tongue. They have also been reported to eat juvenile frogs of other species.
Oregon Spotted Frog tadpoles are grazers, eating algae, decaying plant matter, and detritus.
At present there are only a few populations of Oregon Spotted Frogs in B.C., all in the Fraser Valley. Oregon Spotted Frogs are also found in Washington and Oregon (of course!) and were once found in California, populations that have since been lost. The frog may be seen in the spring in breeding ponds, where the males may be seen and heard calling during the day. Very little is known about the habits of Oregon Spotted Frogs outside the breeding season.
The specialised habitat requirements of Oregon Spotted Frogs have made them extremely vulnerable to extinction. Historic populations have been lost as a result of habitat loss, while it appears that existing populations are declining. Floodplain soils are very fertile, making them desirable for human uses, and much of the historic range of Oregon Spotted Frogs has disappeared under farms and houses. Human alteration of the flood patterns of rivers has also affected Oregon Spotted Frog habitat. From presently known populations, it appears there are only about three hundred Oregon Spotted Frogs in B.C.
Oregon Spotted Frog populations are now widely separated, and this presents a new set of problems, because fragmented populations are known to be particularly susceptible to extinction. Exotic or introduced species of plants and animals also pose a threat to Oregon Spotted Frogs. Bullfrogs, native to Eastern Canada, were accidentally introduced to B.C. forty or fifty years ago. These large frogs can eat Oregon Spotted Frogs and other smaller frogs, and wetlands where Bullfrogs are found have much smaller populations of native amphibians. Green Frogs, another introduction from Eastern Canada, may compete with Oregon Spotted Frog and other B.C. frogs for food. Fish introduced to waterways and wetlands for sport fishing may prey on native frog tadpoles or compete with native frogs for prey. Invasive plants such as reed canarygrass can alter the wetland habitats so much that native frogs can no longer use them.
Oregon Spotted Frogs were declared an Endangered species in Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1999. The species is also Red-listed in B.C.
In 1999, the Oregon Spotted Frog Recovery Team was formed to coordinate efforts to protect this species. The team has members from provincial, federal and regional district agencies, First Nations, universities, and conservation organizations. They are monitoring breeding sites, identifying important habitat, and may some day reintroduce these frogs to previously occupied areas.
The Oregon Spotted Frog is protected under the British Columbia Wildlife Act.
You can help by learning more about these frogs and other amphibians, and telling others about them. You can find out more about ways to protect wetlands through programs such as Naturescape, Wetlandkeepers, and Wild BC. Be an ambassador for the frogs in council meetings and other planning meetings! You can also help biologists learn more about the range, distribution and habits of these and other amphibians by joining B.C. Frogwatch and observing the frog populations near you. The more we learn about frogs in general, the better we can help the Oregon Spotted Frog, together!
- The species name “pretiosa” means “precious” in Latin.
- The main visible difference between Oregon and Columbia Spotted Frogs is the amount of mottling on the belly – leave it to the biologists to tell them apart!
- The Oregon Spotted Frog is the only organism that has received an “emergency listing” as an endangered species in Canada.
Photo © Wally Edwards. No reproduction or distribution without permission.