BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Scaphiopus intermontanus | Great Basin Spadefoot 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Breeding:  Great Basin spadefoots breed in spring and early summer.
Hovingh and others [10] reported that in the Bonneville Basin of Utah,
breeding occurred from April to mid-June.  Breeding after early summer
is probably uncommon.  Spring rains usually provide the stimulus for
males to emerge from their burrows for breeding, although unlike other
spadefoots (Scaphiopus spp.), Great Basin spadefoots do breed during
periods of no rainfall.  The stimulus for emergence for breeding in the
absence of rain is unknown.  Males move to breeding waters first and
begin vocalizing.  Female Great Basin spadefoots move to breeding waters
after only a few males are vocalizing [10].

Each female produces several hundred eggs contained in a sticky gel.
The female deposits her fertilized eggs in several different locations
within the breeding water:  on vegetation, rocks, or anything else that
anchors the eggs.  After mating, females return to their burrows.
Males stay at the breeding pool and continue vocalizing until females
stop arriving (presumably because all females in the vicinity have
mated); then the males also return to their burrows [3].

Development:  Developing rapidly helps Great Basin spadefoots avoid
desiccation and consequent death in their arid environment.  Great Basin
spadefoot eggs probably hatch within 2 to 3 days of deposition [15].
Tadpole development and metamorphosis is complete within 4 to 8 weeks,
depending upon temperature, food quality, and food quantity.  Brown [4]
found that recently fertilized Great Basin spadefoot egg masses,
collected on 20 May from a temporary pond in eastern Washington and
placed in an aquarium, hatched a day later.  Hindlegs of tadpoles in the
aquarium developed by 18 days of age, and forelimbs developed by 31
days.  Tadpole body mass was greatest at 33 days, when complete head
reorganization (eyes, ears, jaws, muscles, and gill absorption) was
complete.  Tail length was greatest 30 days after hatching; the tail was
reabsorped 40 days after hatching [4].  In the wild, temporary waters
frequently dry out and tadpoles die before larval development is
complete [3,4].  Rate of tadpole development may vary with breeding pool
type.  In Texas, tadpoles of a related species, Couch's spadefoot
(Scaphiopus couchii), were found to develop more slowly in permanent
waters than in temporary ponds [14].

Young morphs (metamorphosed preadults) are small; Nussbaum and others
[15] reported that recently metamorphosed Great Basin spadefoots in
north-central Oregon averaged 0.8 inch (19 mm) in length [16].  (Adults
are from 1.5 to 2.5 inches [3.7-6.4 cm] long [18].)  Great Basin
spadefoots have high surface-to-volume ratios as morphs.  Consequently,
they are highly susceptible to desiccation and seek shade cover
immediately after emerging from breeding pools.  Young spadefoots grow
rapidly.  Under laboratory conditions, Couch's spadefoot morphs showed a
110 percent increase in length and over a 1,100 percent increase in mass
in a 3-month period [16].

Hibernation:  Spadefoots accumulate fat rapidly in summer. They are
dormant in fall and winter, with dormancy and apparently triggered by
photoperiod [16].  Spring emergence may be triggered by increased
moisture in the burrow [3].

Spadefoots extend their dormancy period during drought, and can
apparently remain dormant or mostly dormant for long periods of time.
Fat reserves are metabolized slowly during dormancy, and females may
reabsorb their eggs if spring rains do not occur.  Mayhew [12]
speculated that Couch's spadefoots in the extremely arid Imperial Valley,
California, survived a 20-year local drought by remaining dormant except
during rare summer thunderstorms.


PREFERRED HABITAT : 
Great Basin spadefoots occupy cold desert and arid grassland habitats at
low to high elevations.  Great Basin spadefoots have been found at 8,500
feet (2,600 m) elevation in Wyoming [3].  Morph and adult Great Basin
spadefoots live in burrows.  They dig the burrows with their
spade-shaped hindfeet, then cover the burrow entrance with soil.  The
only time they normally emerge from their burrows is when air is moist
[3].

Breeding occurs in spring runoff pools, reservoirs, permanent and
temporary springs, irrigation ditches, and basin lakes [10].  During
their short tadpole life stage, Great Basin spadefoots live in these
breeding waters [3,4].  Great Basin spadefoots usually do not utilize
strongly alkaline water:  Hovingh and others [10] found that most
breeding waters contained less than 1,000 mg/L of dissolved solids.
Breeding sites often have greatly fluctuating volumes of water that
evaporate by autumn.  In the Bonneville Basin, breeding pools with
adundant vegetation showed less tadpole recruitment than pools with
sparse vegetative growth.  The most successful breeding sites were
streambeds scoured by flash floods, reservoirs that had large draw-downs
of water (and thus lacked a littoral zone of vegetation), and temporary
waters that dried by autumn [10].


COVER REQUIREMENTS : 
Morphs and adult Great Basin spadefoots normally venture from their
burrows at night, when it is rainy or the night air is humid enough for
dew to collect [15].  Captive spadefoots (Scaphiopus spp.) have been
observed to dig shallow burrows in moist soil, then dig deeper (2 to 3
feet [0.7-1.2 m]) as soil dries at the surface.  Spadefoots have been
found 15 feet (4.6 m) underground in natural conditions.  An individual
spadefoot digs and occupies only one burrow, which it usually returns to
after foraging or mating.  Darkness provides hiding security during
feeding; spadefoots do not use shrubs or other vegetation for cover
while foraging.  Mating occurs in generally open water [3].


FOOD HABITS : 
Adult spadefoots are opportunistic carnivores.  Adults hunt in spring
and summer, but only at night or during light rains.  A variety of
species of insects, arachnids, and snails have been found in the
stomachs of adult spadefoots.  Tadpoles feed on nearly every type of
water-borne organic matter:  algae, rotting vegetation, bacteria- or
other humus-rich mud, insects, and the bodies of dead tadpoles.
Spadefoot tadpoles are dimorphic.  Within a cohort, some tadpoles have
large mouthparts, while others have much smaller mouthparts.  As well as
consuming other types of food, large-mouthed individuals are
cannibalistic, swallowing other tadpoles whole [3,20].


PREDATORS : 
Mud turtles (Kinosternon flavescens), spotted skunks (Spilogale
putarius) [13], raccoons (Procyon lotor) [5], common crows (Corvus
brachyrhynchos), and other tadpoles [9] have been noted to prey upon
spadefoot tadpoles.  Many other animal species probably prey on both
tadpole and morph Great Basin spadefoots.  Predators of adult Great
Basin spadefoots have not been described in current literature, although
predation of adults is thought to occur [10].  Predation is probably
reduced by the primarily nocturnal habit of adults [3].  In addition,
adult Great Basin spadefoots secrete an odorous, skin-burning mucous
from the paratoid glands when bitten or handled; they may also
regurgitate when bitten or handled.  Many predators are probably
deterred by these traits [19].


MANAGEMENT CONSIDERATIONS : 
Increased irrigation and range improvements in the Great Basin have
benefitted the Great Basin spadefoot [15].  Hovingh and others [10]
noted that on their Bonneville Basin study area, only 8 percent of
breeding waters utilized by Great Basin spadefoots were entirely
natural.  Populations have declined where water has been diverted,
however.


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Scaphiopus intermontanus | Great Basin Spadefoot