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The Columbia spotted frog is a candidate for listing
under the Endangered Species Act.
Background
Columbia spotted frogs were formerly classified as part
of Rana pretiosa, or Spotted frogs. However, Spotted frogs
are now classified as two separate species, the Oregon spotted frog (Rana
pretiosa) and the Columbia spotted frog (Rana luteiventris)
(Green et al. 1997). Researchers found that while the two species
are nearly identical morphologically, they differ genetically and occupy
different ranges (Green et al. 1997).
Historic Status and Current Trends
The species formerly occurred in scattered localities in eastern
Oregon. It still occurs in Deschutes, Crook, Grant, and Union Counties
and is believed to occur in other eastern Oregon counties. Extirpation
from much of its former range coincides with the introduction and
spread of bullfrogs.
Description and Life History
Columbia spotted frog (spotted frog) adults are light to dark brown,
gray, or olive green with dark spots on the back, sides and legs. The
number of spots and spotting pattern varies. The undersides of the
legs are orange or yellow; this color may extend up to the chin
or be replaced by a light, mottled gray on the chin, chest, and/or
belly. Adult
body length is 46 to 90 millimeters (1.8 to 3.5 inches). Spotted
frogs breed during a short, two-week breeding window anywhere from
early April to early June. Eggs
are laid at the water surface in large, globular masses of 200 to
500 eggs. Tadpoles are black after hatching and their eyes are located
on the top of the head. Tadpoles are approximately 8 to 10 millimeters
(0.3 to 0.4 inches) in length at hatching and commonly metemorphose
at 70 to 75 millimeters (2.7 to 3 inches). Metamorphosis
usually occurs from late July until freezing weather. The lifespan
of spotted frogs can be seven to nine years (Engle 2001). Spotted
frog diets can vary widely. Adults eat insects, mollusks, crustaceans,
and arachnids; larvae eat algae and organic debris. Predators of
spotted frog adults include herons and garter snakes, and the recently
introduced bullfrogs. In addition, larvae may be consumed by the
larvae of dragon flies, predacious diving beetles, fish and garter
snakes.
Habitat
Spotted frogs are highly aquatic and live in or near permanent bodies
of water, including lakes, ponds, slow streams and marshes; movements
of spotted frogs are limited to wet riparian corridors. Spotted frogs
occur in riparian areas, where emergent vegetation and standing water
are present, within the sage-juniper shrublands (Engle 2001). Standing
water, flooded meadows, and willows provide breeding, foraging, and
overwintering habitat. Most spotted frogs hibernate (spend winter
in a dormant state) and aestivate (spend summer in a dormant state);
hibernation occurs in spring-fed ponds with willows (Engle 2001).
Range
Columbia spotted frogs occur from Alaska and most of British Columbia
to Washington east of the Cascade Mountains, Idaho, the Bighorn
Mountains in Wyoming, the Mary’s, Reese, and Owyhee River systems in Nevada,
the Wasatch Mountains, and the western desert of Utah. There are currently
four recognized populations of Columbia spotted frogs: Northern, Great
Basin, Wasatch, and West Desert. Columbia spotted frogs within the
Northern population are considered to be abundant; however, the
other three populations (Great Basin, Wasatch, and West Desert) are either
declining or almost extirpated (locally extinct).
Reasons for Decline
The causes of decline are not fully understood, but like most amphibians
a major threat is the destruction, fragmentation and degradation of
wetlands. The
introduction of non-native predators such as bullfrogs, bass, and
predatory freshwater fish species are believed to contribute to the
spotted frog's decline.
References
Csuti, B.; Kimmerling, A. J.; O'Neil, T.A.; Shaughnessy, M.M.;
Gaines, E.P.; Huso, M.M.P. 1997. Atlas of Oregon Wildlife. Oregon
State University Press. 492pp.
Engle, J.C. 2001. Population Biology and Natural History of Columbia
spotted frogs (Rana luteiventris) in the Owyhee Uplands of Southwest
Idaho: Implications for Monitoring and Management. M.S. Thesis, Boise
State University, Boise, Idaho. 66 pages.
Gomez, D. 1994. Conservation assessment for the spotted frog (Rana pretiosa) in
the Intermountain Region, USFS. U.S. Forest Service; Ogden, Utah.
Green, D. M.; H. Kaiser; T.F. Sharbel; J. Kearsley; K. R. McAllister. 1997. Cryptic
Species of Spotted Frogs, Rana pretiosa Complex, in Western North America. Copeia
1997:1-8.
U.S. Fish and Wildlife Service. 2007. Review of Native Species That Are
Candidates for Listing as Endangered or Threatened; Annual Notice of Findings
on Resubmitted Petitions; Annual Description of Progress on Listing Actions;
Proposed
Rule 72(234): 69033-69106.
Marshall, D.B., M.W. Chilcote, and H. Weeks. 1996. Species at
risk: sensitive, threatened and endangered vertebrates of Oregon.
2nd edition. Oregon Department of Fish and Wildlife., Portland,
OR.
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