Index of Species Information
WILDLIFE SPECIES: Anaxyrus boreas
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| A western toad in Squak Mountain State Park, WA. Wikimedia Commons image by Walter Siegmund. |
Introductory
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:
www.fs.usda.gov/database/feis/animals/amphibian/anbo/all.html
[].
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 DISTRIBUTION AND OCCURRENCE
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].
BIOLOGICAL DATA AND HABITAT REQUIREMENTS
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].
FIRE EFFECTS AND USE
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
1. Aubry, Keith B.; Hall, Patricia A. 1991. Terrestrial amphibian communities in the southern Washington Cascade Range. In: Ruggiero, Leonard F.; Aubry, Keith B.; Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 327-338. [17325]
2. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]
3. Brown, David E. 1982. Californian evergreen forest and woodland. In: Brown, David E., ed. Biotic communities of the American Southwest--United States and Mexico. Desert Plants. 4(1-4): 66-69. [8887]
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5. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]
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7. Gilbert, Frederick F.; Allwine, Rochelle. 1991. Terrestrial amphibian communities in the Oregon Cascade Range. In: Ruggiero, Leonard F.; Aubry, Keith B.; Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 319-324. [17324]
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17. Thomas, J. W. 1978. Species list: birds, mammals, fish, reptiles, and amphibians for the Forest Service. Misc. Publ. . Washington, DC: U.S. Department of Agriculture, Forest Service. 82 p. [21138]
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21. Welsh, Harwell H., Jr.; Lind, Amy J. 1991. The structure of the herpetofaunal assemblage in the Douglas-fir/ hardwood forests of northwestern California and southwestern Oregon. In: Ruggiero, Leonard F.; Aubry, Keith B.; Carey, Andrew B.; Huff, Mark H., technical coordinators. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 395-411. [17330]
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]
23. Martin, David L. 1992. Sierra Nevada anuran guide. San Jose, CA: Canorus Ltd. Press. 28 p. [21343]
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26. Komarek, E. V., Sr. 1969. Fire and animal behavior. In: Proceedings, annual Tall Timbers fire ecology conference; 1969 April 10-11; Tallahassee, FL. No. 9. Tallahassee, FL: Tall Timbers Research Station: 161-207. [13531]
27. Raphael, Martin G. 1988. Long-term trends in abundance of amphibians, reptiles, and mammals in Douglas-fir forests of northwestern California. In: Szaro, Robert C.; Severson, Kieth E.; Patton, David R., technical coordinators. Management of amphibians, reptiles, and small mammals in North America: Proceedings of the symposium; 1988 July 19-21; Flagstaff, AZ. Gen. Tech. Rep. RM-166. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 23-31. [7105]
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29. Crane, Marilyn F. 1982. Fire ecology of Rocky Mountain Region forest habitat types. Final Report Contract No. 43-83X9-1-884. Missoula, MT: U.S. Department of Agriculture, Forest Service, Region 1. 272 p. On file with: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. [5292]
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FEIS Home Page
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