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WILDLIFE SPECIES:  Anaxyrus boreas
A western toad in Squak Mountain State Park, WA. Wikimedia Commons image by Walter Siegmund.


WILDLIFE SPECIES: Anaxyrus boreas
AUTHORSHIP AND CITATION : Sullivan, Janet. 1994. Anaxyrus boreas. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. Revisions: The Taxonomy section of this review was updated on 23 October 2018. The image was also added. ABBREVIATION : ANBO COMMON NAMES : western toad boreal toad alkali toad California toad southern California toad TAXONOMY : The scientific name of western toad is Anaxyrus boreas (Baird and Girard) (Bufonidae) [41,42,43]. SYNONYMS : Anaxyrus boreas subsp. boreas, western toad Anaxyrus boreas subsp. halophilus (Baird and Girard), alkali toad, California toad, southern California toad [42] Bufo boreas Baird and Girard [13,16] ORDER : Anura CLASS : Amphibian FEDERAL LEGAL STATUS : None OTHER STATUS : Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe.


WILDLIFE SPECIES: Anaxyrus boreas
GENERAL DISTRIBUTION : The range of western toad extends from western British Columbia and southern Alaska south through Washington, Oregon, and Idaho to northern Baja California, Mexico; east to Montana, western and central Wyoming, Nevada, the mountains and higher plateaus of Utah, and western Colorado [15]. Occurrences of the western toad from Yukon Territory, the Northwest Territories, and northwestern and north-central British Columbia have been reported [36]. Southern records of western toads in New Mexico have been published [35]. ECOSYSTEMS : FRES20 Douglas-fir FRES21 Ponderosa pine FRES22 Western white pine FRES23 Fir-spruce FRES24 Hemlock-Sitka spruce FRES25 Larch FRES27 Redwood FRES28 Western hardwoods FRES29 Sagebrush FRES30 Desert shrub FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES37 Mountain meadows STATES : AK CA CO ID MT NV OR UT WA WY BC Mexico BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau KUCHLER PLANT ASSOCIATIONS : K001 Spruce - cedar - hemlock forest K002 Cedar - hemlock - Douglas-fir forest K003 Silver fir - Douglas-fir forest K005 Mixed conifer forest K006 Redwood forest K007 Red fir forest K011 Western ponderosa forest K012 Douglas-fir forest K014 Grand fir - Douglas-fir forest K018 Pine - Douglas-fir forest K023 Juniper - pinyon woodland K025 Alder - ash forest K029 California mixed evergreen forest K030 California oakwoods K038 Great Basin sagebrush K041 Creosotebush SAF COVER TYPES : 207 Red fir 211 White fir 215 Western white pine 217 Aspen 222 Black cottonwood - willow 229 Pacific Douglas-fir 230 Douglas-fir - western hemlock 239 Pinyon - juniper 241 Western live oak 243 Sierra Nevada mixed conifer 246 California black oak 247 Jeffrey pine 250 Blue oak - gray pine PLANT COMMUNITIES : The western toad is found in the Rocky Mountains in aspen (Populus spp.) groves and riparian forests [8]. In Colorado, the largest populations are typically found in areas characterized by willows (Salix spp.), bog birch (Betula glandulosa), and shrubby cinquefoil (Potentilla fruticosa) [41]. In the Pacific Northwest, the western toad occurs in mountain meadows and less commonly in Douglas-fir forests (Pseudotsuga menziesii) [8]. In California, optimum habitat for the western toad includes wet or dry mountain meadows or riparian deciduous forest with available open water for breeding. Suitable habitat includes blue oak (Quercus douglasii) savanna, gray pine-oak forest (Pinus sabiniana-Quercus spp.), mixed conifer forest, and alpine meadows. Marginal habitats include annual grasslands, chaparral, ponderosa pine forests, California black oak woodlands, Jeffrey pine forests, and red fir forests [20]. In the Sierra Nevada, the western toad occurs in mid-elevation pine forests (including Jeffrey pine (Pinus jeffreyi) at higher elevations and ponderosa pine (Pinus ponderosa) at lower elevations), California black oak woodlands [Quercus kelloggii], giant sequoia groves (Sequoiadendron giganteum), montane fir forest (which includes white fir [Abies concolor], red fir (A. magnifica), and western white pine [P. monticola]), and redwood forest (Sequoia sempervirens). It is also found in riparian areas within sagebrush-pinyon communities (Artemisia spp.-Pinus spp.), oak-pine woodland and savanna (including coast live oak (Q. agrifolia), interior live oak (Q. wislizenii), and canyon live oak (Q. chrysolepis)), and California coastal forest and scrub [8]. Western toads have been collected from sedge meadows near a pond occurring in a creosotebush (Larrea tridentata) community, and from aspen (Populus spp.)-willow groves within big sagebrush (Artemisia tridentata)-grassland [15].


WILDLIFE SPECIES: Anaxyrus boreas
TIMING OF MAJOR LIFE HISTORY EVENTS : Seasonal Activity: Western toads are active from January to October, depending on latitude and elevation [16]. Western toads in one Colorado population used natural chambers near a small stream bed. The high water table, constantly flowing stream, and deep winter snow served to maintain the air temperature within the hibernaculum at a point slightly above freezing. Emergence from hibernation followed a few days of warm temperatures that freed the entrance and increased temperatures within the chamber to about 39.2 degrees Fahrenheit (4 deg C) [40,41]. Diurnal Activity: At low elevations western toads are active at night; at high elevations and in the northern parts of their range they are diurnal [16]. Body temperature of western toads is closely correlated with the substrate temperature. Basking and conduction from the substrate are primary means of increasing body temperature and cooling is achieved by evaporative cooling and conduction of heat to a cooler medium. Diurnal and nocturnal activity are often related to seasonal changes in temperature; most western toads are diurnal during the spring and fall but are nocturnal during the warmer summer months [41]. Minimum Breeding Age: In central Oregon, the minimum breeding age for male western toads is 3 years, and probably 4 or 5 years for females [10]. California toads are reported as sexually mature at 2 years of age [11]. Male western toads breed every year; females breed at less regular intervals, depending on individual condition and previous years' breeding effort [10]. Sex ratios differ according to habitat type; males are more numerous in wet areas and females are more numerous in dry habitats [41]. Breeding Season: Eggs are laid in open water from February to July, with peak activity occurring in April. Timing of egg-laying activity varies with elevation and weather conditions [20]. In Colorado, initiation of breeding was correlated with the onset of warming weather and initiation of snowpack melting. Eggs are usually laid in late May or early June [41]. In western Montana, a few males were present on the shores (of two gravel pits) by May 11, 1967, and by May 14, each pond contained at least 30 males. Males were spaced at least 1 foot (.3 m) apart, all facing the shore [33]. Clutch Size: Eggs are laid in gelatinous strings of 13 to 52 eggs per inch, in masses of up to 16,500 per clutch [15,24]. Egg development rate is partially dependent on temperature; hatching times vary [11]. Development of Young: Metamorphosis is usually completed within 3 months of egg laying. The time required for metamorphosis is given as 30 to 45 days for the western toad and 28 to 45 days for the California toad [15]. Longevity: Female western toads at least 10 to 11 years of age have been reported [10]. In Colorado, western toads probably attain a maximum age of at least 9 years [41]. PREFERRED HABITAT : Western toads are widespread throughout the mountainous areas of northwestern North America, ranging from sea level to elevations near or above regional treeline, or 10,000 feet (305-3,050 m) in elevation [15,20]. It is uncommon at the higher elevations [20]. Elevational range in Colorado is from about 7,000 feet to 11,860 feet (2,131-3615 m). In the mountains of Colorado, the largest western toad populations usually occur from about 9,500 feet to 11,000 feet (2,896-3,353 m) elevation [34]. Western toads occupy desert streams and springs, grasslands, and mountain meadows; they are less common in heavily wooded regions. They are usually found in or near ponds, lakes (including saline lakes), reservoirs, rivers, and streams within the above mentioned habitats [15,16]. Under laboratory conditions western toads were able to survive in 40 percent seawater, but died within a week when exposed to 50 percent seawater [11]. In Colorado, individual western toads typically maintain distinct ranges which vary greatly in size according to the condition of the habitat. Breeding males may exhibit territoriality, especially in areas where breeding sites are scarce [41]. Populations of western toads have very limited dispersal, particularly in rugged terrain [10]. Breeding Habitat: Western toads require open water for breeding [20]. All breeding members of a local population tend to lay their eggs in the same location, which is used repeatedly from year to year. For example, at one site on a permanent lake in the Oregon Cascade Range, western toads returned each year to the same submerged willow clumps [10]. Eggs are usually laid in shallow water (not deeper than 12 inches [30 cm] but usually at least 6 inches [15 cm]) [10,24]. The warmth of shallow water increases the rate at which development occurs; shallow water and vegetative matter may contribute to protection of eggs from predation by fish [10]. In western Montana, breeding western toads used gravel pits that were only filled with water during spring runoff. These gravel pits contained cattails (Typha spp.) but no other vegetation, and were 5 feet (1.5 m) deep in the center [33]. COVER REQUIREMENTS : Western toads are terrestrial. Their body temperatures are largely controlled by basking and evaporative cooling. In order to avoid evaporative conditions, they usually spend the daylight hours on the forest floor in the soil under rocks, logs, stumps, or other surface objects or in rodent burrows [8,11,15,16,24]. Individuals have been observed to use the same retreat repeatedly. In locations where there is little or no hiding cover, western toads may spend most of the day in the water [15]. Under more humid conditions, western toads may become active during the day [11]. Breeding Cover: western toads lay their eggs in water; they require some form of surface cover near the egg-laying location. Woody debris or submerged vegetation is used to protect egg masses [10,24]. FOOD HABITS : Western toads wait for their prey on the surface of the ground or in shallow burrows dug by other animals. Their diet consists largely of bees, beetles, ants, and arachnids. Other foods include crayfish, sowbugs, grasshoppers, trichopterans, lepidopterans, and dipterans [15,20]. PREDATORS : Tadpoles are preyed upon by fish, herpetiles, birds, and mammals [11]. Toads in general tend to walk or hop rather than jump (like frogs). Their slow movement renders them vulnerable to predators; however, the western toad (like other toads) produces skin toxins that are avoided by many predator species. The nocturnal habit may help reduce predation [8]. Adult western toads are preyed upon by common ravens (Corvus corvax) and probably by other birds, herpetiles, and mammals as well [10,11]. A badger (Taxidea taxus) was recorded as having consumed five adult Anaxyrus (probably western toad, as it was the only Anaxyrus species in the area) in Wyoming [37]. MANAGEMENT CONSIDERATIONS : Reproductive success of western toads depends on amount of snowpack and rate of snowmelt which determine the persistence of breeding pools used by western toad populations [33]. Amphibians generally seem to be more sensitive to environmental changes than other taxonomic groups. Western toads repeatedly use individual stumps or logs, which may be an important consideration for conservation and recovery programs. They are also vulnerable to mass predation by common ravens during breeding periods when large numbers of toads congregate at egg-laying sites. It was observed that such mass predation did not occur when humans were in close proximity to the toads. The authors speculated that human activity may play a role in common raven activity pattern, and could contribute indirectly to mass predation episodes. Since the entire breeding effort of a population is concentrated in one location, mass predation on eggs can have severe consequences to population recruitment. The eggs are also vulnerable to catastrophic loss due to freezing, lowering of water levels, and other disturbances. Human activities such as logging and/or prescribed burning may have a negative effect on breeding congregations or on massed eggs by reducing woody debris in and near the water, reducing available shade, and pressuring predators to move from human activity sites to sites where western toad breeding is occurring [10]. In northwestern California, however, western toads were slightly more abundant in early brush/sapling stages of postharvest Douglas-fir forest compared to later stages or undisturbed forest; they are therefore classified as increasers after logging [28]. The water level of breeding pools could also be affected by human activity at critical times. The absence of nonbreeding adult females from breeding congregations provides some protection (at the population level) from population decline due to mass predation. More than half of females skipped at least 1 year between breeding years at study sites in the Oregon Cascade Range [10]. Mortality of western toads is greatest during the larval and juvenile stages, but is slight thereafter. Most mortality can be attributed to unseasonable weather and predation on juvenile toads. There is very little predation on adult toads and mortality of adults is low [41]. Western toads are taken by humans for the pet trade [23].


WILDLIFE SPECIES: Anaxyrus boreas
DIRECT FIRE EFFECTS ON ANIMALS : There is no published information on mortality of western toads from fire. The fact that there are no reports of high mortality for any herpetile species may indicate that amphibians and reptiles are not highly vulnerable to fire [26]. Kahn [25] reported that western fence lizards (Sceloporus occidentalis) survived a serious chaparral fire by remaining in the soil beneath rocks. Western toads similarly could survive fire by remaining in the soil beneath rocks, entering animal burrows, or by escaping to water; survival in retreats under flammable materials (logs, stumps, and boards) would depend on fire severity and moisture conditions. Komarek [27] states that animals appear to respond to fire with adaptive behaviors which minimize mortality; he reports that experiments with different types of prescribed fires resulted in no discernible amphibian mortality. Frogs escaped a backing fire by travelling ahead of the fire, then burying themselves under wet leaves and soil in a small depression [27]. HABITAT RELATED FIRE EFFECTS : Western toads occupy diverse habitats, some of which experience fire relatively frequently (Douglas-fir forests in drier areas [31]), and some of which rarely experience fire (riparian zones tend to act as fire breaks but will burn during extended dry conditions [30]). No specific information describing the response of western toads and their habitat to fire was available in the literature. Western toads are vulnerable to changes in both terrestrial and aquatic habitat. They are, however, found in slightly higher abundance in early seres of Douglas-fir forests [28]. Severe fires that burn surface objects such as logs and stumps would immediately decrease available hiding cover for western toads, but postfire sprouting of shrubby species would result in a longer-term, overall increase in low hiding cover [30]. Most willow species sprout after top-kill by fire [29], so the amount and thickness of willow clumps increases after fire. Crown fires would reduce shade and surface humidity and decrease the amount of daylight time toads could spend active after a fire. Fires during early spring could affect egg masses by reducing shade and increasing water temperatures. Any substantial change in runoff rates, erosion, or water tables caused by fire could degrade breeding sites. It is likely that there is a change in the relative amounts of different types of prey organisms in the postfire diet of western toads. Immediately after fire, many insects are present but those requiring shade do not adapt well to the more open conditions. In the longer term there are differential responses to fire among prey organisms; ant populations were one-third higher in burned areas than in unburned areas, but beetles tend to decrease on burned areas [32]. FIRE USE : Specific information concerning prescribed fire as it affects western toads was not available in the literature. Conservation of surface objects used for hiding cover is important in any management decision [10]. FIRE REGIMES : Find fire regime information for the plant communities in which western toad may occur by entering the species name in the FEIS home page under "Find Fire Regimes".

References for species: Anaxyrus boreas

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22. U.S. Department of the Interior, Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants; animal candidate review for listing as endangered or threatened species; proposed rule. 50 CFR Part 17. Tuesday, November 15, 1994. Federal Register. 59(219): 58982-59028. [24357]
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