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BC Conservation Data Centre: Species Summary


Anaxyrus boreas
Western Toad


 
Scientific Name: Anaxyrus boreas (Baird and Girard, 1852)
Scientific Name Synonyms: Bufo boreas
English Name: Western Toad
 
Classification / Taxonomy
Scientific Name - Concept Reference: Frost, D. R. 1985. Amphibian species of the world. A taxonomic and geographical reference. Allen Press, Inc., and The Association of Systematics Collections, Lawrence, Kansas. v + 732 pp.
Classification Level: Species
Taxonomy Comments: Changed from Bufo boreas to Anaxyrus boreas (June 2010 - DW).
Species Group: Vertebrate Animal
Species Code: A-ANBO
Kingdom Phylum Class Order Family
Animalia Craniata Amphibia Anura Bufonidae
   
Conservation Status / Legal Designation
Global Status: G4 (Jan 2008)
Provincial Status: S4 (Apr 2022)
BC List: Yellow
Provincial FRPA list:   
Provincial Wildlife Act:
COSEWIC Status: Special Concern (Nov 2012)
SARA Schedule: 1  -  Special Concern (Jun 2018)
SARA Comments: Calling and Non-calling Populations
General Status Canada: 3 - Sensitive (2005)
   
Ecology & Life History
General Description: These warty toads are yellowish, dusky, tan, gray, or greenish on top, with dark markings ranging from a few spots to extensive mottling. Usually a light stripe extends along the middle of the back (most prominent in mature females; may be absent or inconspicuous in juveniles, which may have reddish warts). Parotoid glands (glandular swellings behind each eye) are oval. Cranial crests (hard ridges next to the eyes) are absent or indistinct. The tubercles on the underside of hind feet lack a sharp cutting edge; the foot tubercles are yellowish or orange in juveniles. Adult females are as large as 5 inches (12.7 cm) in snout-vent length, but males rarely exceed 3.7 inches (9.5 cm). Mature males have a dark patch on the inner surface of the thumb during the breeding season. Male lack vocal sacs but may produce repeated chirping sounds if grasped by hand (females usually are silent or emit few chirps). Larvae are black or dark brown on top; the tail fin may be heavily speckled with gray or black;and the eyes are about half way between the midline of the head and outside edge of the head. Larvae may reach a maximum total length about 2 inches (5 cm) but often are much smaller. Eggs are about 1.5-1.8 mm in diameter and are arranged in 1-3 rows (often two rows that appear to be a single zig-zag row) in long strings of two-layered jelly. Source: Hammerson (1999).
Subspecies Comments: There is only one subspecies found within BC, B. b. boreas.
Identification Comments: Adults: Their skin appears dry and bumpy with conspicuous, oval-shaped parotoid glands behind the eyes. They have horizontal pupils and a cream-coloured or white dorsal stripe. Males can reach 60-110 mm long, with the larger females up to 125 mm snout-to-vent length (SVL). The hind feet have horny tubercles used for burrowing. Male toads may emit a release call when grasped. Tadpoles: The larvae are small and black (roughly 12 to 13 mm SVL, or 25 to 30 mm total length prior to metamorphosis), with a square snout, eyes in from the margins of the head, and a narrow tail fin. Eggs: Single long strands or loosely intertwined layed at or below the water surface (Wind and Dupuis 2002).
Global Reproduction Comments: The breeding period varies with local conditions; it may begin in January at low elevations but not until late spring or summer, as the winter snowpack begins to melt, in the high mountains. Females deposit an average of about 12,000 eggs/clutch, in two strands. Eggs hatch in a few days (warm temperatures) or in up to about 12 days (cold conditions). Larvae metamorphose in around 1-3 months, before the next winter; warm conditions result in the fastest larval development. Recently metamorphosed western toadlets sometimes form dense aggregations on the shores of breeding sites. Adult females may skip one or more years between successive breeding events. In northwestern Utah, single-year breeding populations at six sites ranged from a few dozen to nearly 250 individuals (Thompson 2004).
Provincial Reproduction Comments: Western Toads reach sexual maturity between 2-6 years of age; females may reproduce only every 1-3 years, and possibly only once in their life time, while males may breed more than once per year (Olson 1988). Western Toads are explosive breeders, with reproduction occuring for a short period in early spring (e.g., during a one to two week period). Males may or may not emit an advertisement call (varies across the range), but they produce a release call when grasped (Wind and Dupuis 2002). Males amplex the female and there is external fertilization. Toads lay their strings of eggs in shallow, littoral areas, amongst emergent vegetation; they are colonial breeders and they may lay their eggs in the same location within a breeding site annually (Olson 1992). Like other amphibians, toads exhibit high high site fidelity to natal breeding ponds. Females lay approximately 1,500 to 5,000 eggs per clutch (Blaustein et al. 1995), which develop and hatch within 3-12 days depending on water temperature (Leonard et al. 1993; Hengeveld 2000); metamorphosis occurs within three months of egg laying (Stebbins 1951). There is no parental care in toads.
Global Ecology Comments: Ravens were significant predators on breeding toads in Oregon Cascades (Olson 1989). In Colorado, Corn (1993) observed a high rate of predation on breeding adults, evidently by ravens. Crow predation on adults was observed in Idaho (Brothers 1994.
Provincial Ecology Comments: The home range of Western Toads radio-tracked on southern Vancouver Island was less than or equal to approximately 0.1 ha (Davis 2000). Dispersal distance is unknown - adults move 1-2 km, long distance movements of up tp 7.2 km (Davis 2000). A study in Oregon revealed that female toads may only reproduce once in their life time due to the high energy expenditure required for reproduction (Olson 1988). Like all amphibians, toad populations likely fluctuate extensively from year to year in response to climate (e.g., snowfall or precipitation). Tadpoles are highly gregarious, and newly transformed toadlets form large post-metamorphic aggregations; tadpoles transform in their first year. The greatest mortality within Western Toad populations occurs at the tadpole and juvenile stage (Campbell 1970). Western Toad and tadpoles predation observed by snakes (Thamnophis sirtalis) and ravens in BC and elsewhere (Gyug 1996; Davis 2000). Tadpoles are unpalatable to fish and newts (Kiesecker et al. 1996), but there is high predation pressure by predacious diving beetle larvae (Livo 1999). Toads reach sexual maturity in two to six years, and have a life expectancy of nine to 11 years (Campbell 1970; Porter 1972; Green and Campbell 1984; Olson 1988; Carey 1993). Toads may be particularly susceptible to disease and parasite infections.
Migration Characteristics:
(Global / Provincial)		 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant: 		N / 0
Y / Y
N / N
na / N
Global Migration Comments: Migrates seasonally between aquatic breeding and terrestrial nonbreeding habitats.

In Colorado, Muths (2003) found that radio-tracked toads moved up to about 2 km from their breeding sites. Average maximum distance from the breeding site was 905 m in six females and 462 m in 8 males; mean distance of all locations was 721 m in females and 218 m in males; mean minimum distance was 392 m in females and 131 m in males. The longest distance was by a female that moved 2,324 m from her breeding site.

In Idaho, males moved an average of 581 m from the breeding pond and females moved an average of 1,105 m; the greatest total seasonal distances traveled by a male and a female toad were 0.94 km and 2.44 km, respectively (Bartelt et al. 2004). Some individuals remained in the breeding pond area, even after the pond dried.

In northwestern Utah, Thompson (2004) recorded movements of up to 5 km across upland habitat between two springs; the movement occurred between June of one year and January of the next year. Another toad moved 1.3 km between May of one year and May of the next year; the following June it was back at the original breeding location (Thompson 2004).

In Montana, individuals moved along stream corridors; based on recaptures (not radio-tagging), the longest documented movement was 1.5 km upstream in 6 days (Adams et al. 2005).
Provincial Mobility & Migration Comments: Like many other amphibians, Western Toads migrate between aquatic breeding sites, upland summer ranges, and overwintering areas in spring and fall. Radio-telemetry on southern Vancouver Island revealed that adult toads move very little in spring and summer, within small distinct home ranges less than or equal to about 0.1 ha (Davis 2000). Males and females commonly travelled 1-2 km from breeding sites; long-distance movements were occasionally observed (e.g., one toad moved approximately 7.2 km within a 24-hour period) (Davis 2000). Little is know about toadlet dispersal distances, but they are known to move away from aquatic breeding sites en mass, forming large, post-metamorphic aggregations (Wind and Dupuis 2002). On southern Vancouver Island, adult toads moved mainly at night (Davis 2000). Toads are active from spring until fall throughout their range, but in the north of the province they have been observed emerging very early in the year where they are known to breed in hot springs (Slough 2004).
Habitats:
(Type / Subtype / Dependence) 		Forest / Conifer Forest - Dry / Facultative - frequent use
Forest / Conifer Forest - Mesic (average) / Facultative - frequent use
Forest / Conifer Forest - Moist/wet / Facultative - frequent use
Forest / Deciduous/Broadleaf Forest / Facultative - frequent use
Forest / Mixed Forest (deciduous/coniferous mix) / Facultative - frequent use
Grassland/Shrub / Grassland / Facultative - frequent use
Grassland/Shrub / Meadow / Facultative - frequent use
Lakes / Lake / Obligate
Lakes / Pond/Open Water / Obligate
Riparian / Gravel Bar / Facultative - frequent use
Riparian / Riparian Forest / Facultative - frequent use
Riparian / Riparian Herbaceous / Facultative - frequent use
Riparian / Riparian Shrub / Facultative - frequent use
Springs / Warm Spring / Facultative - occasional use
Stream/River / Stream/River / Facultative - frequent use
Wetland / Bog / Obligate
Wetland / Fen / Obligate
Wetland / Marsh / Obligate
Wetland / Swamp / Obligate
Global Habitat Comments: Western toads occur in a wide variety of habitats ranging from desert springs to mountain wetlands. They range into various upland habitats around ponds, lakes, reservoirs, and slow-moving rivers and streams; sometimes they move up to a few kilometers through uplands. For shelter, they dig their own burrow in loose soil or use those of small mammals or seclude themselves under logs or rocks. Egg laying sites include shallow areas of ponds, lakes, or reservoirs, or pools of slow-moving streams.
Provincial Habitat Comments: Western Toads have been observed in a variety of aquatic and terrestrial habitats. They breed in shallow, littoral zones of lakes, temporary and permanent pools and wetlands, bogs and fens, and roadside ditches (i.e., toads may be found in all lacustrine and palustrine habitats); tadpoles associate with benthic habitats. In northern BC and the Yukon, Western Toads have been observed using geothermal springs and surrounding tufa/soils for breeding and hibernacula (Slough 2004). In addition, like many amphibian species, toads utilize riparian areas. Lotic habitats with little to no flow are suitable for toads. Small, moist depressions may be used for reydration (toads can absorb water through their 'pelvic patch') (Green and Campbell 1984; Davis 2000). Toads utilize a variety of terrestrial habitats in BC, including all forest and woodland types, shrubland/chaparral, savanna, cropland/hedgerow, grassland/herbaceous cover, old fields, and suburban/orchard. Hibernacula are located in areas with loose soils and burrows. Toads have been observed using downed wood for cover in recent clearcuts (E. Wind, pers. comm.). Western Toads one of few amphibians found at high elevations (> 3,000 m). Climate change may impact western toads in northern regions of BC where populations are dependent on areas of high snow accumulation, that lack permafrost, to survive through winter (Cook 1977).
Food Habits: Herbivore:Immature
Invertivore: Adult
Global Food Habits Comments: Metamorphosed individuals feed on various small terrestrial invertebrates. Larvae filter suspended plant material or feed on bottom detritus (Nussbaum et al. 1983).
Provincial Food Habits Comments: Adult toads are opportunistic carnivores, feeding mainly on invertebrates in terrestrial and riparian environments, such as worms, spiders, bees, beetles, ants, arachnids, crayfish, sow bugs, grasshoppers, trichopterans, lepidopterons, and dipterans (Wind and Dupuis 2002). Tadpoles are herbivorous, filtering suspended plant material or feeding on benthic detritus in aquatic environments.
Global Phenology: Crepuscular: Adult, Immature
Diurnal: Adult, Immature
Hibernates/aestivates: Adult, Immature
Nocturnal: Adult, Immature
Global Phenology Comments: Activity varies seasonally and geographically. At low elevations, western toads are active in daylight during cool weather of late winter and spring, but most activity is at night during warmer weather. They are active day or night in summer in the mountains, depending on conditions. They remain secluded in winter in cold climates.
Provincial Phenology:
(1st half of month/
2nd half of month)		 Jan: Present / Present
Feb: Present / Present
Mar: Active / Active
Apr: Active / Reproducing
May: Reproducing / Eggs present outside adult
June: Eggs present outside adult / Larvae present and active
July: Larvae present and active / Larvae present and active
Aug: Larvae present and active / Larvae present and active
Sept: Active / Active
Oct: Active / Active
Nov: Active / Present
Dec: Present / Present
Provincial Phenology Comments: Because the habitat range of the Western Toad within BC is so extensive, both latitudinally and elevationally, the active season and breeding period varies extensively through the province. In south-central British Columbia they breed in May (Poll et al. 1984; Gyug 1996), when the average daily minimum temperature is above freezing and the maximum reaches 10 degrees Celsius (Gyug 1996). In coastal areas, they may breed as early as March. In general, toads are active from early spring until late fall; adults emerge and breed in early spring, eggs and tadpoles are present in late spring and summer, and metamorphosis occurs in late summer/early fall. Toads activity varies by region and elevation; e.g., at low elevations, they are nocturnal in summer and diurnal in early spring, but they may be active day and night at higher elevations. Toads are inactive in winter in most areas; at low elevation coastal areas in the south of the province toads may be active at some periods in winter. Studies suggest that amphibians are breeding earlier as a result of climate change (Corn 2000).
Colonial Breeder: Y
Length(cm)/width(cm)/Weight(g): 13/ /
Elevation (m) (min / max): Global: 
Provincial:  0 / 3600
   
 
Distribution
Endemic: N
Global Range Comment: The range extends along the Pacific Coast from southern Alaska (Wiedmer and Hodge 1996) to Baja California, and eastward through the Rocky Mountains to west-central Alberta, Montana (Werner et al. 2004), Wyoming (Baxter and Stone 1985), Utah (Ross et al. 1995, Thompson et al. 2004), Colorado (Hammerson 1999), and (formerly) northern New Mexico (Degenhardt et al. 1996). The species is absent from most of the desert Southwest (Stebbins 2003). Elevational range extends from sea level to more than 11,000 feet (3.355 meters) in some areas in the Rocky Mountains.
 
Authors / Contributors
Global Information Author: Hammerson, G.
Last Updated: Jan 26, 2010
Provincial Information Author: Wind, E.
Last Updated: Dec 03, 2005
   
References and Related Literature
Behler, J. L., and F. W. King. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp.
Blaustein, A.R., P.D. Hoffman, D.G. Hokit, J.M. Kiesecker, S.C. Walls and J.B. Hays. 1994. UV repair and resistance to solar UV-B in amphibian eggs: a link to population declines. Proc. Nat. Acad. Sci. 91:1791-1795.
British Columbia Ministry of Water, Land and Air Protection. 2002e. Western Toad. B.C. Minist. Water, Land and Air Prot., Biodiv. Branch. 2pp.
Brothers, D.R. 1994. Bufo boreas (Western Toad) predation. Herpetological Review 25(3):117.
Campbell, J.B. 1970. Life history of Bufo boreas boreas on the Colorado Front Range. PhD. Diss. Univ. of Colorado, Boulder, CO.
Carey, C. 1993. Hypothesis concerning the causes of the disappearance of boreal toads from the mountains of Colorado. Conserv. Biol. 7:355-362.
Carey, C. 1993. Hypothesis concerning the causes of the disappearance of boreal toads from the mountains of Colorado. Conservation Biology 7(2):355-362.
Cook, F.R. 1977. Records of the boreal toad from the Yukon and northern British Columbia. Can. Field-Nat. 91:185-186.
Corn, P. S. 1993. Bufo boreas (boreal toad) predation. Herpetological Review. 24(2):57.
Corn, P. S., and F. A. Vertucci. 1992. Descriptive risk assessment of the effects of acidic deposition on Rocky Mountain amphibians. J. Herpetol. 26:361-369.
Corn, P. S., W. Stolzenburg, and R. B. Bury. 1989. Acid precipitation studies in Colorado and Wyoming: interim report of surveys of montane amphibians and water chemistry. U.S. Fish and Wildl. Serv. Biol. Rep. 80(40.26). 56 pp.
Corn, P.S. 2000. Amphibian declines: review of some current hypotheses. In D.W.Sparling, G. Linder, C.A. Bishop, eds. Ecotoxicology of Amphibians and Reptiles. U.S. Geol. Sur., Midwest Sci. Cent. Columbia MO, 663-696.
COSEWIC. 2002l. COSEWIC assessment and status report on the western toad Bufo boreas in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 31 pp.
Davis, T.M. 2000. Ecology of the western toad (Bufo boreas) in forested areas on Vancouver Island. Final Rep., For Renewal B.C., Minist. For., Victoria, BC.
Davis, T.M. 2002. Research Priorities for the Management of the Western Toad, Bufo boreas, in British Columbia. B.C. Minist. Water, Land and Air Prot., Biodiversity Branch, Victoria, BC. Wildl. Working Rep. WR-106. 35pp.
Green, D.M., and R.W. Campbell. 1984. The Amphibians of British Columbia. Royal B.C. Mus. Handb. No. 45. 101pp.
Gyug, L. 1996. Part IV Amphibians. In Timber harvesting effects on riparian wildlife and vegetation in the Okanagan Highlands of British Columbia. B.C. Environ., Penticton, BC.
Hailman, J. P. 1984. Bimodal nocturnal activity of the western toad (Bufo boreas) in relation to ambient temperature. Copeia 1984:283-290.
Hammerson, G. A. 1982b. Amphibians and reptiles in Colorado. Colorado Division of Wildlife, Denver. vii + 131 pp.
Hammerson, G. A. 1989. A field survey of amphibians in the Rocky Mountains of Colorado, August 1989. Report to the Colorado Division of Wildlife and the Colorado Natural Areas Program. 53 pp.
Hammerson, G. A. 1992. Field surveys of amphibians in the mountains of Colorado, 1991. Report to the Colorado Division of Wildlife and Colorado Field Office of The Nature Conservancy.
Hengeveld, P.E. 2000. Presence and distribution of amphibians in the Williston and Dinosaur Reservoir watersheds. Peace/Williston Fish and Wildl. Compensation Program Rep. No. 212.
Hodge, R. P. 1976. Amphibians and reptiles in Alaska, the Yukon and Northwest Territories. Alaska Northwest Publishing Company Anchorage, Alaska. 89 pp.
Kiesecker, J.M., D.P. Chivers, and A.R. Blaustein. 1996. The use of chemical cues in predator recognition by western toad tadpoles. Anim. Behav. 52:1237-1245.
Leonard, W., H. Brown, L. Jones, K. McAllister, and R. Storm. 1993. Amphibians of Washington and Oregon. Seattle Audubon Soc., The Trailside Ser., Seattle, WA. 168pp.
Livo, L.J. 1999. Predator communities and boreal toad breeding sites. In M.S. Jones, ed. Colorado Div. Wildl. Boreal Toad Res. Prog. Rep. 1998. Fort Collins, CO.
Nussbaum, R.A., E.D. Brodie, Jr., and R.M. Storm. 1983. Amphibians and Reptiles of the Pacific Northwest. University Press of Idaho, Moscow, Idaho. 332 pp.
Olson, D H. 1992. Ecological susceptibility of amphibians to population declines. In Proc. of the Symp. on Biodiversity of Northwestern California, October 28-30, Santa Rosa, CA.
Olson, D. 1989. Predation on breeding western toads (Bufo boreas). Copeia 1989:391-397.
Olson, D. H. 1992. Ecological susceptibility of high elevation Oregon anuran amphibians to population fluctuations. Abstract, 6th Annual Meeting of the Society for Conservation Biology, p. 102.
Olson, D.H. 1988. The ecological and behavioral dynamics of breeding in three sympatric anuran amphibians. PhD. Diss., Oregon State Univ., Corvallis, OR.
Ovaska, K, S. Lennart, C Engelstoft, L. Matthias, E. Wind and J. MacGarvie. 2004. Best Management Practices for Amphibians and Reptiles in Urban and Rural Environments in British Columbia. Ministry of Water Land and Air Protection, Ecosystems Standards and Planning, Biodiversity Branch
Poll, O.M., M.M. Porter, G.L. Holroyd, R.M. Wershler, and L.W. Gyug. 1984. Ecological land classification of Kootenay National Park, B.C. Volume II. Wildlife Resource. Can. Wildl. Serv., Edmonton, AB.
Porter, K.R. 1972. Herpetology. W.B. Sanders Co. Philadelphia, PA.
Ross, D. A., T. C. Esque, R. A. Fridell, and P. Hovingh. 1995. Historical distribution, current status, and a range extension of Bufo boreas in Utah. Herpetological Review 26:187-189.
Samallow, P.B. 1980. Selective mortality and reproduction in a natural population of Bufo boreas. Evolution 34(1):18-39.
Slough, B.G. 2004. Western Toad inventory in the Chilkoot Trail National Historic Site, July-August 2004. Parks Can. Species at Risk Inventory Fund Proj. SARINV04-30. Rep. to Parks Can. Yukon Field Unit, Haines Junction, YT. 54pp.
Smits, A. W. 1984. Activity patterns and thermal biology of the toad Bufo boreas halophilus. Copeia 1984:689-696.
Stebbins, R. C. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.
Stebbins, R.C. 1951. Amphibians of Western North America. University of California Press. Berkeley, CA.
Wind, E., and L. Dupuis. 2002. Status of the Western toad Bufo boreas in Canada. Rep. for the Comm. on the Status of Endangered Wildl. in Can. (COSEWIC), Can. Wildl. Serv., Environ. Can., Ottawa.
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 2010. Species Summary: Anaxyrus boreas. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed May 9, 2025).