BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Bufo boreas | Western Toad 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Seasonal Activity:  Western toads are active from January to October,
depending on latitude and elevation [16].  Boreal 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 temperatues 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 boreal 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, boreal toads probably attain a maximum
age of at least 9 years [41].
 


PREFERRED HABITAT : 
Western toads are widespread througout 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 Bufo (probably western toad, as it was the only Bufo 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 persistance 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].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Bufo boreas | Western Toad