Western Toad

Name: Western Toad (Bufo boreas)

(also known as Boreal Toad, Northwestern Toad)

Status: Federal Candidate (1999), State Candidate (WA, ID), Sensitive Species (OR)

Description: A large toad with dry, bumpy skin, two horny tubercles on hind feet, distinct oval parotoid glands, and horizontal pupils. Coloration ranges from reddish-brown to gray to olive green. A cream-colored stripe runs down the middle of the back. The underside is yellow or cream color with dark blotches. Size: male- up to 4 ¼ inches, female- up to 5 inches. Tadpoles aggregate and are dark in color. Adults are distinct from other frogs and toads in that they walk rather than hop.

Threats: Habitat loss, degradation and fragmentation, other environmental changes.

Photo by Gerald and Buff Corsi

Ecology:

Western Toads are mostly terrestrial and live in habitats ranging from mountain meadows to desert flats. They are most common around marshes and small lakes. The toads are nocturnal at lower elevations and diurnal at higher elevations. During the day they burrow in the soil, using the horny tubercles on their hind feet to assist in digging, or else hide in woody debris or the abandoned burrows of small mammals. In the northern, colder climates, they hibernate during the winter. Adults feed on flying insects, spiders, crayfish and earthworms. Larvae eat suspended plant material and detritus. Western Toads are preyed upon by garter snakes, coyotes, raccoons, and some birds such as crows and ravens. When the toads are threatened they excrete a mild white poison from their parotoid glands and warts. Breeding season varies depending on ice and snow melt, and can occur from late January through July. In the lower elevations west of the Cascades, breeding can occur from February to April, and at higher elevations in the Cascades, breeding doesn’t occur until May or early July. Males do not have a mating call like most other frogs and toads. Females deposit eggs in two long strings of up to 2 meters in length, with an average of 12,000 eggs per clutch. Eggs are surrounded by two gel layers, which distinguish them from Woodhouse’s Toad egg, which have a single gel layer.

Population Trends and Possible Threats:

Western Toads have a historical range in the lowlands of western Washington and meadows of the North Cascades. According to surveys by Leonard et al. (1993), while once abundant in those areas they are now uncommon. They also appear to be in decline in the Greater Yellowstone Ecosystem and other parts of the Western U.S. (Leonard et. al.). Western Toads, like most amphibians, are sensitive to changes in environmental conditions. UV-B radiation has been shown to cause reduced hatching success of Western Toads in Oregon (Blausein et al. 1994, Garcia), but not in Colorado (Corn, 1998, Garcia). UV-B radiation has also been shown to increase the growth of the alga Saprolegnia ferax, which infects communal egg masses such as those laid by Western Toads (Kiesecker and Blaustein, 1997, Garcia). More research in these areas is still needed. Loss of habitat, principally wetlands, is another factor believed to contribute to the Western Toad’s decline.

Current Distribution:

The Western Toad is widely distributed throughout the western U.S. The subspecies B. b halophilus is found from California to Baja California, and the subspecies B. b. boreas is found from Alaska down through California and New Mexico (Garcia). The Western Toad can be found in all of Washington except the more arid regions of the Columbia basin, and in all of Oregon except the northern Coast Range and most of the Willamette Valley. They live at a variety of elevations, from sea level up to 7,370 feet in the Steens Mountains in Oregon (Leonard et al., 1993).

References:

Blaustein, Andrew R., Hoffman, P. D., Hotkit, D. G. Kiesecker, J. M., Walls, S. C., and Hays, J.B. (1994). UV repair and resistance to solar UV-B in amphibian eggs: A link to population declines? Proceedings of the national Achedemy of Sciences of the United States of America, 91(5) 1791-1795.

Garcia, Erica. Bufo boreas AmphibiaWeb page. Online: http://elib.cs.berkeley.edu/aw (Accessed 7/26/00).

Kiesecker, J.M., and A.R. Blaustein, (1997). Influence of egg laying behavior on pathogenic infection of amphibian eggs. Conservation Biology, 11(1), 214-220.

Leonard, W. P., Brown, H. A., Jones, L.C., McAllister, K. R. and R.M. Storm, (1993) Amphibians of Washington and Oregon. Seattle Audubon Society. Seattle, Washington.

Peterson, Charles R. Atlas of Idaho’s Wildlife in PDF. Digital Atlas of Idaho: Preliminary Beta Version.

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