Males attract females to temporary breeding pools with loud calls while they are partially submerged in the water. These calls may also attract other males who will compete for the females. The calls are short, between 1 and 3 notes long, and duck-like. Because Spea intermontana is nocturnal, it has large eyes probably adapted to seeing at night. Great Basin spadefoot toads likely perceive their environment through a minimum of audio, visual, tactile and chemical stimuli.
Communication Channels: tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
Spea intermontana may sometimes be referred to as Spea intermontana.
Some studies place Spea intermontana as a sister group to to Spea bombifrons and suggest that S. intermontana is in fact paraphyletic.
Total adult population size is not knows but exceeds 10,000. The species has no special conservation status and populations seem to be stable. Natural habitats have mostly not been subject to threat, though agriculture has reduced and threatened some populations. Irrigation, however, could be creating new habitats, as it creates standing water sources necessary for breeding in areas previously inhospitable to the toads. Man-made reservoirs also account for a sizable number of breeding sites. The fact that the toads are generalized in their feeding habits is also good news for the survival of the species; the elimination or reduction of a particular species of prey will not significantly impact the availability of food. In general, Great Basin spadefoot toads have a good chance of survival wherever standing water is available and wherever soil allows for burrowing.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
Eggs usually hatch within 2 to 4 days. Tadpoles transform in about 30 to 40 days, but the rate of metamorphosis can increase if the temporary pools in which the larvae are developing begin to dry out. Growth and differentiation rates are also influenced by temperature, which affects thyroid hormone activity (thyroid hormone is involved in metamorphosis). It is critical that larvae develop rapidly in species that breed in temporary pools, such as Spea intermontana, because metamorphosis must occur before the water evaporates, as the tadpoles cannot survive outside of water. Transformed juveniles still have a tail which disappears soon after they leave the breeding pools, and they may remain at the breeding location for a period of several days to several weeks before they leave the site. Transformed juveniles develop into sexually mature adults in 1 to 2 years for males, and in about 2 years for females.
Development - Life Cycle: metamorphosis
When threatened, adult Great Basin spadefoot toads can produce noxious skin secretions which may cause minor allergic reactions in humans, symptoms of which may include sneezing and a runny nose, and may also cause a burning sensation upon contact with the eyes and nose.
There are no known positive impacts of Great Basin spadefoot toads on humans.
Great Basin spadefoot toads affect populations of the arthropods they prey on. Due to the relative stability of their populations, the species also helps maintain the populations of its predators, as the toads are a relatively consistent source of food. They have no symbiotic or mutualistic interactions with any other species. Parasites that infect the species include Polystoma nearcticum in the lung and bladder, Distoichometra bufonis in the small intestine, Aplectana incerta in the small and large intestine, species of the genera Physaloptera (larvae) in the stomach, and Acuariidea (larvae) in cysts on the stomach wall.
Commensal/Parasitic Species:
Adult Great Basin spadefoot toads are insectivores and carnivores who feed primarily at night. They are generalists, feeding on easily captured terrestrial insects and other arthropods. One study found that adult toads consumed at least 56 different arthropod taxa from the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Orthoptera, Trichoptera, Collembola, and Araneae. Due to their abundance in the native habitats of Great Basin spadefoot toads, ants and darkling beetles are the most common sources of prey. Great Basin spadefoots do not have any particular preference, however, for one prey type over another. Toads are limited to eating species small enough for them to swallow whole, and tend not to eat species that produce noxious secretions, such as certain types of ground beetles. While plant matter has been found in the stomach contents of the toads, vegetation is not a primary source of food for adults of the species.
Little information is available regarding the feeding habits of Great Basin spadefoot toad larva. Tadpoles of spadefoot toads are omnivorous; they feed on water-born plant material such as algae, organic detritus, and small plants, as well as insects and other amphibian larvae. Tadpoles also feed on carrion and may even become cannibalistic, especially in breeding pools. Carnivorous larvae are able to grow and metamorphose faster due to the higher level of protein in their diet.
Animal Foods: amphibians; carrion ; insects; terrestrial non-insect arthropods
Plant Foods: algae; phytoplankton
Other Foods: detritus
Primary Diet: carnivore (Insectivore )
Great Basin spadefoot toads are found in the United States and Canada. The species occurs in northwest Arizona, in California east of the Sierra Nevada mountain range, northwestern Colorado, lower Idaho, southwestern Wyoming, throughout Nevada and Utah, and between the Cascade and Rocky Mountain ranges in Oregon, Washington, and British Columbia.
Biogeographic Regions: nearctic (Native )
Great Basin spadefoot toads are found in arid regions, semi-desert shrubland, or sagebrush flats, but can also be found in alkali flats, pinion-juniper woodland, ponderosa pine, and high elevation spruce-fir forests at about 2800 m (9200 ft). Great Basin spadefoot toads require temporary or permanent water sources for breeding, such as slow-flowing springs, seasonal pools, irrigation ditches, and ponds. They are able to survive in arid habitats by remaining buried underground, thus their survival requires soils that permit burrowing.
Range elevation: 2800 (high) m.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: desert or dune ; chaparral ; forest ; scrub forest ; mountains
Aquatic Biomes: temporary pools
The lifespan of Great Basin spadefoot toads is unknown. It is assumed to be similar to other spadefoot toad species and is therefore estimated to be about 13 years for females and 11 years for males in the wild.
Typical lifespan
Status: wild: 11 to 13 years.
Great Basin spadefoot toads usually have a gray, olive, or brown colored dorsal coloration mottled with darker spots with light-colored centers. Gray streaks outline an hourglass shaped marking on the back. The coloration is similar to that of other species of the genera Spea and Scaphiopus. Ventral coloration is light gray, white, or creamy and without markings. The skin is relatively smooth compared to the rough, warty nature of true toads (genus Bufo), but still contains small bumps. Parotoid glands seem to be absent. There is a dark brown or orange spot present on each upper eyelid. Pupils are vertical, and the eyes are large, catlike, golden yellow, and located on the side of the head. The nose is slightly upturned and there is a raised callus between the eyes. The body is short and fat with stubby limbs. Spadefoot toads get their name from the presence of a black, keratinized spade, or tubercle, on the underside of each hind foot, which is used for burrowing behavior. Adult body lengths vary from 32 to 67 mm and females tend to be only slightly larger than males. Tadpoles have large globular bodies and can reach 70 mm in length. They are colored black, brown, and gaey with scattered golden specks. When threatened, adult Great Basin spadefoot toads can produce noxious skin secretions, which are probably poisonous or at least distasteful to predators.
Range length: 32 to 67 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: sexes alike; female larger
Adult Great Basin spadefoot toads are preyed upon by western rattlesnakes, coyotes, and burrowing owls. Tadpoles are mainly preyed upon by western terrestrial garter snakes and American crows. When water levels rise high enough to flood breeding pools, tadpoles are also preyed upon by rainbow trout and brown trout.
When threatened, adult Great Basin spadefoot toads can produce noxious skin secretions, which are reported to smell like popcorn or roasted peanuts. The skin secretions are probably poisonous or at least distasteful to predators. They may even cause minor allergic reactions in humans, symptoms of which may include sneezing and a runny nose, and may also cause a burning sensation upon contact with the eyes and nose. Burrowing and camouflaged coloration may also help adult spadefoots escape predation. By contrast, tadpoles are comparatively helpless and have few defenses against predation other than cryptic coloration.
Known Predators:
Anti-predator Adaptations: cryptic
Great Basin spadefoot toads are explosive breeders, with all breeding completed in a few days. There is no specific or definite breeding season, but all breeding takes place from May through August, when temperature and water availability is favorable. There is much variation in the timing of mating each year due to the nature of mating locations. Adults are terrestrial, but breeding sites are located around water sources. As a result, adults of the species must migrate to the breeding sites. These journeys typically occur at night in order to limit exposure to dangers such as evaporative water loss and predation. The factors that stimulate mating are not very well understood. Rainfall may be one of them, but is not necessary for it as is the case with other spadefoot toad species. Adults migrate anywhere from 1 to 5 km to reach breeding sites.
The breeding pools may be permanent or temporary sources of water, such as rain-water pools, snowmelt, ponds, irrigation ditches, and streams. Breeding is more common in ephemeral water sources in areas where it rains enough to create temporary pools, and more common in permanent water sources in areas where it does not rain enough to create temporary pools. The water must be still or slow-moving to allow breeding. In order to support metamorphosis, breeding pools must remain filled for at least 40 days to allow enough time for eggs to hatch and for larval transformation.
Males migrate to breeding sites, partially submerge near the shore, and attempt to attract females using loud calls 1 to 3 notes in length. The calls, or choruses, are reported to be monotonous duck-like snoring sounds, and may be heard over great distances. The choruses attract females, and probably other males, to the breeding pools. As females arrive, males scramble and compete to find mates. Reproduction involves amplexus, where males embrace females from behind using their forelimbs. This position allows males to externally fertilize the female eggs as they emerge from the females' cloacae. When mating is completed, the adults quickly burrow underground to avoid evaporative water loss.
Mating System: polygynandrous (promiscuous)
After mating, females lay anywhere from 300 to 1000 eggs in small clusters of 10 to 40 eggs. They attach the egg clusters to floating sticks, submerged rocks, and underwater vegetation. Eggs usually hatch within 2 to 4 days, but may take longer if water temperatures are too cold. Their size at sexual maturity is unknown. Males mature sexually in the first 1 to 2 years after metamorphosis, while females do not sexually mature until at least the second year after metamorphosis.
Breeding interval: Great Basin spadefoot toads breed an average of once yearly if conditions are favorable.
Breeding season: Great Basin spadefoot toads will breed from May through August when conditions are favorable.
Range number of offspring: 300 to 1000.
Range time to hatching: 2 to 4 days.
Average age at sexual or reproductive maturity (female): 2 years.
Range age at sexual or reproductive maturity (male): 1 to 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
There is no parental involvement in the care for young once the eggs are laid. Females lay and attach their eggs to vegetation in bodies of water, and subsequently migrate back to feeding habitats, along with males, to replenish their energy reserves.
Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female)
The Great Basin spadefoot (Spea intermontana) is an amphibian in the family Scaphiopodidae. It is 3.8 to 6.3 centimetres (1.5 to 2.5 in) long and is usually colored gray, olive or brown. Great Basin spadefoot toads have adapted to life in dry habitats. They use the hard, keratinized spade on each foot to dig a burrow, where they spend long periods during cold and dry weather. They are opportunistic hunters and will eat anything they can subdue. While their tadpoles have numerous predators, adults are able to produce skin secretions that deter enemies.
The Great Basin spadefoot ranges from 3.8 to 6.3 centimetres (1.5 to 2.5 in) long.[3] It is usually gray, olive or brown colored. Gray streaks outline an hourglass-shaped marking on the back. The skin is smooth compared with the bumpy skin of the true toads in the genus Bufo. There is a spade present on the inside of each hind foot; it has sharp edges and is wedge-shaped. A glandular boss is present between the eyes. Eyes are catlike; pupils are vertical in bright light and round at night. Dark brown spots are present on each upper eyelid.
The natural habitats of the Great Basin spadefoot include pinyon-juniper, ponderosa pine, and high elevation (up to 2,600 metres or 8,500 feet[4]) spruce-fir forests, semidesert shrubland, sagebrush flats, temperate grasslands, and deserts. They are present in agricultural areas as well. The Great Basin Spadefoot can be found from southern British Columbia through the eastern portions of Washington and Oregon and in southern Idaho. Their range extends throughout all of Nevada and into most of Utah; they are also present in small areas in California, Arizona, Colorado, and Wyoming.[3][5]
Breeding is explosive, meaning that large congregations of individuals assemble and mate with each other. Adults are terrestrial and must migrate to breeding sites. Breeding may take place in permanent or temporary water sources such as springs, sluggish streams, and manmade reservoirs during the months of April through July. 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 breeding in the absence of rain is unknown. Males move to breeding waters first and begin vocalizing.[6] Once females arrive, there is a race to mate with as many others as possible, and physical contests between males are common.
Females usually lay 300–500 eggs contained in a sticky gel, but have been reported lay as many as 1000 eggs in captivity. The female deposits her fertilized eggs in several different locations within the breeding water: on vegetation, rocks, bottom of the pool, 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.[4]
Eggs hatch in 2 to 4 days,[7] and the tadpole development and metamorphosis is complete within 4 to 8 weeks, depending upon temperature, food quality, and food quantity. Developing rapidly helps Great Basin spadefoots avoid desiccation and consequent death in their arid environment.[4]
Young morphs (metamorphosed preadults) are small, about 0.8 inch (19 mm) in length on average.[7][8] They have high surface-to-volume ratios; therefore, they are highly susceptible to desiccation and seek shade cover immediately after emerging from breeding pools. They grow, by about 110% in length and 1,100% in mass over 3 months under laboratory conditions.[8] Tadpoles may be carnivorous or herbivorous, depending on environmental conditions. Different larval diets are associated with different morphological characteristics.[9]
Adult spadefoots are opportunistic carnivores. Adults have been shown to eat arthropods from the taxa Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Orthoptera, Trichoptera, Collembola, and Araneae. Ants and beetles are their most common prey. Feeding seems to be generalized and opportunistic; the toads will eat anything they can subdue.[4]
Adults hunt in spring and summer, but only at night or during light rains. 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.[4][10]
Reported predators of adult Great Basin spadefoot toads include rattlesnakes, coyotes, and owls. Predators of larva include mud turtles (Kinosternon flavescens), spotted skunks (Spilogale putarius),[11] raccoons (Procyon lotor),[12] common crows (Corvus brachyrhynchos) and snakes. Adults are able to produce skin secretions that cause allergic reactions in some humans, including a burning sensation if the secretion gets in the eyes or nose. The skin secretions also deter predators.[13]
Great Basin spadefoot toads have adapted to life in dry habitats. Desiccation is avoided by this terrestrial amphibian through burrowing into the ground. The toad use the hard, keratinized spade on each foot to dig a burrow, where it spends long periods during cold and dry weather. The toad is able to absorb water from the surrounding soil; even as the soil becomes increasingly dry in spring and early summer months, increased concentrations of urea in the toad's body allow it to continue to suck water out of the soil through osmosis. When the summer rains arrive the Great Basin spadefoot emerges from its burrow.[4]
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.[7] Captive spadefoots 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. Spadefoots do not use shrubs or other vegetation for cover while foraging.[4]
Spadefoots accumulate fat rapidly in summer. They are dormant in fall and winter, with dormancy apparently triggered by photoperiod.[8] Spring emergence may be triggered by increased moisture in the burrow.[4] 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.[9]
This article incorporates public domain material from Scaphiopus intermontanus. United States Forest Service.
{{cite journal}}: CS1 maint: multiple names: authors list (link) {{cite journal}}: CS1 maint: multiple names: authors list (link) The Great Basin spadefoot (Spea intermontana) is an amphibian in the family Scaphiopodidae. It is 3.8 to 6.3 centimetres (1.5 to 2.5 in) long and is usually colored gray, olive or brown. Great Basin spadefoot toads have adapted to life in dry habitats. They use the hard, keratinized spade on each foot to dig a burrow, where they spend long periods during cold and dry weather. They are opportunistic hunters and will eat anything they can subdue. While their tadpoles have numerous predators, adults are able to produce skin secretions that deter enemies.
