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Photo by Paul Thompson
Courtesy the Utah Division of Wildlife Resources
Western toad
Anaxyrus boreas
Other common names: Boreal toad
NatureServe conservation status
Global (G-rank): G4
State (S-rank): S3
- Reason: Although still fairly widely distributed and moderately common in Utah, this species is known to be greatly reduced in both abundance and distribution in this state. Populations have disappeared from many areas of its historically known occurrence in Utah.
External links
General information
The western toad, Anaxyrus boreas, inhabits western Canada and much of the western (especially northwestern) United States. It occurs throughout most of Utah, and can be found in a variety of habitats, including slow moving streams, wetlands, desert springs, ponds, lakes, meadows, and woodlands. The western toad, which is inactive during cold winter months, may either dig its own burrow in loose soil or use the burrows of other small animals.
Adults feed on numerous types of small invertebrates, such as ants, beetles, and grasshoppers, whereas larvae (tadpoles) filter algae from the water or feed on detritus. Adults are dusky gray or greenish in color with considerable dark blotching on the back and belly, and can usually be identified by a light-colored stripe along the back. The breeding season of the western toad varies, depending on geographic location.
Phenology
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.
Species range
Known from areas of high elevation, mainly the Wasatch Mountains and central high plateaus, from Rich and Daggett counties in the northeast to Washington and Kane counties in the southwest; also a few high areas near the Nevada border in Box Elder County.
Migration
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).
Food habits
Tanner (1931) presented data on stomach contents of this species in Utah: ants and beetles of several families were found in stomachs of most of the seven specimens examined; seven caterpillars were in one stomach, and a grasshopper was in another. Titus (1910) reported large numbers of weevil larvae and adults in stomachs of toads of this species found in cultivated fields in Utah.
Ecology
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.)
Reproductive characteristics
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).
Threats or limiting factors
Habitat loss is a widely recognized contributing factor, and has undoubtedly played a role in some population losses, especially populations formerly occupying what are now urban areas. Chytrid fungus (Batrachochytrium dendrobatidis) has been implicated in declines elsewhere, but does not appear to have contributed to the loss of populations in Utah (C. Bailey, UDWR, pers. comm.). Many of the population changes that have been detected remain unexplained.
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
- Stebbins, R. C. 1985. A field guide to western reptiles and amphibians. Houghton Mifflin Company, Boston. 336 pp.
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