Oregon spotted frog
Rana pretiosa
Habitat
Oregon spotted frogs are highly aquatic. They are found in or near permanent still water, such as lakes, ponds, springs, marshes, and the grassy margins of slow-moving streams. They have been found at elevations up to 5,150 feet (1570 meters).
Physical Description
Adults weigh 25-90 grams, with females being larger at maturity. Mature females, measured snout to rump, range from 2.4-3.9 inches long (60-100 mm), mature males range from 1.8 to 2.9 inches (45-75 mm).
They are robust, solid-looking frogs. Their color ranges from olive green to brown to brick red, with individuals tending to redden with age. They are patterned with many large, irregular black spots with indistinct edges (and often, lighter-colored centers). Their undersides are mottled with red or orange, which appears painted onto the surface of the skin rather than penetrating deeply into it. Eyes are upturned and greenish-yellow in color. A ridge runs along each side of the frog’s back, starting right behind each eye and fading away as they reach the hindquarters. Oregon spotted frogs can be differentiated from similar species by their relatively short legs and webbing on their back feet that reaches all the way to the ends of the toes.
Life Expectancy
A maximum of five to eight years in the wild, though most do not live that long. The species has not been widely maintained in captivity until very recently, so no typical captive lifespan has been determined.
Diet
In the wild: Tadpoles graze on algae and rotting vegetation, with the bacteria living on the decomposing plant material providing important nutrition. Adults are carnivores, feeding primarily on insects, spiders, and earthworms.
At the zoo: Tadpoles eat a pureed mixture of boiled romaine, kale and spirulina. When they become juvenile frogs, they are fed live crickets.
Reproduction
Male Oregon spotted frogs reach sexual maturity at about two years of age; females, not until age three. Breeding season begins in late winter to mid-spring, depending mainly on elevation, and lasts about three weeks. Males congregate in shallow water along wetland margins or on floating vegetation mats, often in water less than six inches deep, and emit advertisement calls to females. The call is faint, and sounds much like a woodpecker tapping on a tree in the far distance. When a female is ready to lay her eggs, she approaches the group of males. The first male she encounters will seize her from behind with his forelegs in an embrace called amplexus. She will lay her eggs in the shallow water, and his grasp places him in the ideal position to fertilize the eggs as they are laid. The egg mass is smaller than an orange when first laid, but expands to many times that size within hours as the jelly around the eggs absorbs water. Females arriving later will lay their eggs next to, or even on top of, the egg masses already there. After laying her eggs, each female will immediately return to her solitary life. The males remain in the breeding pond as long as a month, calling to attract additional females that may show up later in the season. Often, the first larvae are starting to hatch before the final males have given up and left.
Life Cycle
Eggs hatch in 18-30 days, depending mainly on water temperature. Initially, the eggs hatch into fairly immobile larvae, which remain in or on top of the gradually liquefying jelly. In about a week, they are free-swimming tadpoles. It takes 13-16 more weeks for the tadpoles to metamorphose into juvenile frogs. The juveniles start out roughly half the size of adults, and are light olive green to light brown, with a cream-colored underside. As they grow, they develop their darker, redder adult coloration.
Everything Old Might Be New to Us
Oregon spotted frogs look so similar to another species, the Columbia spotted frog (Rana luteiventris), the two were considered variations of the same species until 1997. While the two species look almost identical, they live in distinctly different habitats, and their ranges do not overlap. Additionally, geneticists discovered in the late 1990’s the two species are actually much more distantly related than had ever been imagined. Another difference is their conservation status. The Columbia spotted frog is thriving in its habitat, but not so for the Oregon spotted frog.
Before it was known there were two distinct species involved, it seemed spotted frogs were declining in some marginal areas, but otherwise thriving throughout most of their range. This new information revealed an entire species, the Oregon spotted frog, rapidly disappearing. Scientists and regulatory agencies had to act fast, and the legal status of the Oregon spotted frog is in a state of flux as new information comes in.
Location at the zoo
Oregon spotted frogs at Woodland Park Zoo are not currently on exhibit. Instead, they are part of a captive headstarting program WPZ participates in along with partners including Northwest Trek Wildlife Park, Oregon Zoo, Cedar Creek Correctional Facility, and the Washington Department of Fish and Wildlife. (See below for more information.)
You can see other fascinating amphibian species in many areas of the zoo, including the Day Exhibit and the Tropical Rain Forest. Species include Panamanian golden frogs, poison dart frogs, smooth-sided toads, and axolotls.
Conservation Connection
Since they have only recently been determined to be a distinct species, the legal status of the Oregon spotted frog varies widely by region. The governments of Canada and the state of Washington classify them as endangered. The US federal government currently classifies the species as a candidate for endangered status. The International Union for the Conservation of Nature (IUCN) lists them as vulnerable.**
The overall population of the Oregon spotted frog is decreasing. The total number of the frogs in the wild is estimated to have decreased 30% in just the last 15 years. The primary threat to the frogs is the loss of habitat. The shallow wetlands required for breeding are also the easiest to drain and fill for agriculture or new construction. While adult Oregon spotted frogs can live in deeper water outside of the breeding season, they cannot reproduce successfully without significant expanses of water just a few inches deep. Very few of these wetlands still exist within their range. Furthermore, the few remaining breeding areas now present the added threat of introduced predators, such as the locally non-native American bullfrog and exotic game fishes, such as the large-mouth bass. In addition to these problems, the amphibian specific chytrid fungus (Batrachochytrium dendrobatidis) has been identified at every Oregon spotted frog occupied site. This fungus is likely responsible for many amphibians’ mortalities and may be one important reason for recent declines in Oregon spotted frog populations.
The Oregon spotted frog is an important species in many respects. They are a predator of insects, including species that in large enough numbers can damage food crops or spread disease to humans and domestic animals. In addition, they are also an important source of food (both as tadpoles and adults) to many larger native predators. These include, but are not limited to, garter snakes, roughskin newts, mink, otters, red foxes, kingfishers, greater sandhill cranes, and great blue herons. Amphibians also fill an important role as indicators of the cleanliness of our water supply. The skin of frogs and other amphibians can easily absorb chemical pollutants, so changes in the health of these animals are often a first sign that a watershed has become contaminated. Would you want water that can kill a frog coming out of your faucet?
Woodland Park Zoo Is Helping—With Your Support!
The zoo’s captive headstarting program is part of Washington state’s efforts to protect the Oregon spotted frog. Eggs are collected in the spring from the few remaining breeding ponds, are raised to fully metamorphed frogs in a protected captive environment. In the fall, they are released back into a protected wetland area in hopes to boost their population numbers and help them avoid extinction. This project is modeled after recovery programs in British Columbia, where survival rates have improved when large numbers of juvenile frogs are all released at the same time.
The Oregon spotted frog headstarting project is one of four captive breeding and release projects at the zoo; the others are for western pond turtle and Oregon silverspot butterfly. In addition to species recovery work, the zoo also supports conservation efforts around the globe through its Partners for Wildlife program. Learn more at How You Can Help.
How You Can Help!
The effort to save animal species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Let your elected representatives know your views on protecting endangered species and wild habitats. Please do not buy products made from wild animal parts.
You can help the zoo’s conservation projects directly by donating via our website. Learn other ways you can help conserve wildlife and the habitats they require for survival, by calling the zoo's Education Center at 206.684.2424.
Sources and Suggested Reading
Jones, Lawrence L.C., Leonard, W.P. & Olson, D.H. (eds.) (2005). Amphibians of the Pacific Northwest. Seattle Audubon Society.
Corcran, Charlotte C. & Thoms, Chris (2006). Amphibians of Oregon, Washington, and British Columbia. Vancouver: Lone Pine Publishing.
McAllister, K. R. and W. P. Leonard (1997). Washington State status report for the Oregon Spotted Frog. Olympia: WA Department of Fish and Wildlife.
Backhouse, Frances (2002). Wildlife in British Columbia at risk: Oregon spotted frog. Victoria: Ministry of Water, Land and Air Protection.
Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, & T. A. Dewey (2008). Rana pretiosa. In: The Animal Diversity Web (online). Accessed 17 September 2009 at http://animaldiversity.org.
Geoffrey Hammerson & Christopher Pearl 2004. Rana pretiosa. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1 (online). Accessed 16 September 2009 at www.iucnredlist.org.
AmphibiaWeb: Information on amphibian biology and conservation (2009). Berkeley, California (online). Accessed 30 September 2009 at http://amphibiaweb.org/.
For Kids!
Whiting, Jim (2007). Frogs in Danger (On the Verge of Extinction: Crisis in the Environment series). Mitchell Lane Publishers. 32 pages. Ages four to eight.
Hamilton, Garry (2004). Frog Rescue: Changing the future for endangered wildlife. Firefly Books. 64 pages. Ages nine to 12.
Turner, Pamela S. (2009). The Frog Scientist. Houghton Mifflin Books for Children. 64 pages. Ages nine to 12.
Other References
Amphibian Conservation Alliance at http://www.frogs.org. A nonprofit organization dedicated to promoting the conservation of amphibians. Lots of amphibian information, including current news stories.
The Exploratorium: Frogs at http://www.exploratoruim.edu/frogs. The online component of the former Frogs exhibit at San Francisco’s Exploratorium. Information and activities especially suitable for children.
American Museum of Natural History’s Frogs: A Chorus of Colors at http://www.amnh.org/exhibitions/frogs/
More great information (and beautiful pictures), this time from the American Museum of Natural History in New York. A great place to hear recorded frog calls, too.
Washington Department of Fish and Wildlife
For more information about the Oregon spotted frog pilot reintroduction project,
http://wdfw.wa.gov/do/newreal/release.php?id=nov1709b
*Taxonomic classification varies between references. Classification information used in this fact sheet was taken from: IUCN Red List of Threatened Species. Version 2009.1 (online). Accessed 16 September 2009 at www.iucnredlist.org.
**There are several international and federal agencies that determine the endangered status of species. WPZ designates a species as endangered if it is listed as endangered on the IUCN (International Union for the Conservation of Nature) Red List, the US Fish & Wildlife Service's Endangered Species List, or on Appendix I of CITES (Convention on the International Trade of Endangered Species of Flora and Fauna).