The Oregon Spotted Frog is one of BC rarest amphibians and is found only in the Fraser Valley. Four populations are documented: Mountain Slough, Bertrand Creek, Maria Slough, Morris Valley (Mike Pearson pers. comm. 2013). Collections reported from the BC interior are erroneous (Mike Pearson pers. comm. 2013).
This species can be confused with the Red-legged Frog (Rana aurora).
Species Description
Oregon spotted frogs and Columbia spotted frogs are very similar in appearance. They can be olive, tan, light brown to reddish brown, with light-centred black spots scattered over their backs. As colouration and patterning can vary, particularly in juveniles, spotted frogs can be easily confused with Red-legged Frogs and even juvenile Green Frogs. A light tan stripe on the upper jaw extends back to the shoulder, and a faint, dark eye mask may be visible. The underbelly of the species is whitish, with reddish-orange tinges appearing as though they were painted onto the lower belly and legs. In adults, bones on the undersides of the hind legs cannot be seen through the skin.
Diet
Adults and Juveniles are sit-and-wait ambush predators, feeding on invertebrates, insects and earthworms. They have been observed eating dragonflies, damselflies, spiders, as well as juvenile western toads. Tadpoles feed on algae and detritus.
Reproduction
AmphibiaWeb (2009) provides the following information on reproduction of Oregon Spotted Frog: ' breeding occurs sometime in February or March at lower elevations, and adults exhibit strong fidelity to breeding sites; males arrive first, gathering in "lek-like" groups and float in the shallows, calling while awaiting the arrival of a female; most breeding occurs over a two-to-three-week period, although interruptions to this can occur during periods of cold weather; ted; females usually lay their eggs atop or adjacent to other egg masses (some of the larger aggregations may contain more than 100 individual egg masses), and they are deposited in still, shallow water; sometimes, the the upper portions of the egg masses protrude above the water surface resulting in severe egg mortality from freeze-thaw damage or desiccation; egg development takes several weeks then thousands of small tadpoles emerge and cling to the remnants of the gelatinous egg masses; after several days, the tadpoles become free-swimming tadpoles, they may grow to 90 mm total length before metamorphosing in their first summer or fall, mortality of eggs, tadpoles, and newly metamorphosed frogs is high, and it is likely that only about 1% of an annual cohort survive to the first winter; near sea-level sexual maturity is attained at age two, while at higher elevations one or two additional years is required."
Habitat
The Oregon Spotted Frog breeds in shallow, warm water marshes associated with permanent bodies of water (Haycock 2000), which have decreased greatly in the past century due to human encroachment (e.g., agricultural draining, urban development). They prefer habitat that is under 30 cm deep, with a variety of emergent vegetation at a medium density and complex submerged vegetation structure. Overwintering has been observed in beaver dams, culverts, shrub roots, woody debris, seeps, springs, and shallow silt.
Distribution
The Oregon Spotted Frog is another member of the family Ranidae (true frogs). Its known historical distribution is discontinuous, and includes areas in northern California, western Oregon, the Puget Basin of Washington, and the Lower Mainland of British Columbia. It is now extirpated from some of these areas, in some cases up to 90 percent of its former range. (Natureserve.org Species Explorer, 2005). Based on allozymal variation, this species was only recently recognized as a distinct species from the much more widely distributed Columbian Spotted Frog (Rana luteiventris; Green et al. 1997) which ranges from central Wyoming northwest to the Alaskan panhandle and northwestern BC. In B.C., the Oregon Spotted Frog is at the northern extent of its range. The species currently occurs only in extremely small populations in isolated wetland sites in the Fraser River Lowlands .
Conservation Concerns
An enormous amount of habitat for this species was lost when the seasonally flooded wetland area known as Sumas Lake, east of Abbotsford in the Fraser Valley, was dyked and drained in the early 1900s. Introduced species may also be a threat, particularly Bullfrogs, and invasive reed canary grass (Phalaris arundinacea), which overgrows the shallow, warm waters in which Oregon Spotted Frogs breed and forage. Reed canary grass is found in every site in B.C. known to contain these frogs (Haycock 2000). The Oregon Spotted Frog has a habit of communal egg-laying which has also contributed to its decline. Several females will lay their eggs in the exact same spot piled on top of each other. If the water at that location undergoes a change in depth, temperature, water chemistry – anything that can potentially harm developing embryos - then some or all of the egg masses can be lost.
Read the COSEWIC report for this species here.
View a short documentary video of the Oregon Spotted Frog, produced by Isabelle Groc and Mike McKinley, and narrated by researcher Monica Pearson.
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