Spea intermontana

A small toad of the family Pelobatidae, the genus is characteristically short-legged and squat, having vertical "cat-eye" pupils, and a black, keratinized spade (used for burrowing) on the underside of each hind foot.Their skin is relatively smooth compared to the rough, warty epidermis of truetoads (genus Bufo). Females are slighty larger than males. Distinguishing features include a slightly upturned, "pug-nose", a raised callus, or boss, between the eyes, and a dark brown or orange spot on each upper eyelid. Dorsal coloration is similar to that of other Spea and Scaphiopus species: Usually a brown, gray, or olive background, mottled with darker spots posessing light-colored centers. The ground color is variable and often matches the substrate. The venter is light gray, white, or creamy.

Tadpoles have large, globular or ovoid bodies, reaching 70 mm in total length. Their dorsal coloration is black, brown, or dark gray and flecked with metallic golds and rusts, while the abdomen displays an overall golden irridescence. The spiracle is located low on the abdomen, and to the left side.

This species lives in western North America, in the United States and Canada. In Calfornia, they occur east of the Sierra Nevada, and north of San Bernardino Co. They occur throughout Nevada and Utah east of the Colorado River, push just south into northwest Arizona, and north into northwest Colorado and southwest Wyoming. In Canada, Washington and Oregon, they are sandwiched between the Cascade and Rocky Mtn. ranges, but occur throughout lower Idaho. They are found in arid regions, often associated with high desert scrub and sagebrush, but also reach past the pinion-juniper woodland, and into the spruce-fir belt at about 2800 m (9200 ft).

Little is known about abundance due, in part, to its explosive breeding habits, but it is often heard in temporary pools and flooded ditches immediately after winter and spring rains.

Activity varies with local conditions, but it is most active during and after winter, spring, and sometimes summer rains, when it may emerge to breed or forage on wet nights.

This species can be in Southern British Columbia, Canada (Cannings 1999) southward in the USA through central and eastern Washington and Oregon, southern Idaho, eastern California, Nevada, Utah, Wyoming, and northwestern Colorado to northwestern Arizona (Hall 1998). It can be found from the edge of Cascade-Sierra axis east to the Rockies. It is found at elevations of about 850m asl (Stebbins 1985).

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 )

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Southern British Columbia (Cannings 1999) southward through central and eastern Washington and Oregon, southern Idaho, eastern California, Nevada, Utah, Wyoming, and northwestern Colorado to northwestern Arizona (Hall 1998). From edge of Cascade-Sierra axis east to the Rockies. To elevations of about 9,200 ft (Stebbins 1985).

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

Length: 5 cm

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

Spea intermontana is 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

Comments: Mainly sagebrush flats, semi-desert shrublands, pinyon-juniper woodland. Digs its own burrow in loose soil or uses those of small mammals. Breeds in temporary or permanent water, including rain pools, pools in intermittent streams, and flooded areas along streams. Eggs are attached to vegetation in water or placed on bottom of pool.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Migrates up to several hundred meters between breeding pools and nonbreeding terrestrial habitats.

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 spadefood 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 )

Comments: Not well documented. Adults known to eat insects. Larvae probably eat algae, organic debris, plant tissue, etc., sometimes invertebrates and amphibian larvae.

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:

• Lung and bladder parasites Polystoma nearcticum
• Intestinal parasites Distoichometra bufonis
• Intestinal parasites Aplectana incerta
• Stomach parasites Physaloptera (larvae)
• Stomach parasites Acuariidea (larvae)

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:

• Western rattlesnakes (Crotalus viridis)
• Coyotes (Canis latrans)
• Burrowing owls (Athene cunicularia)
• Western terrestrial garter snakes (Thamnophis elegans)
• American crows (Corvus brachyrhynchos)
• Rainbow trout (Oncorhynchus mykiss)
• Brown trout (Salmo trutta)

Anti-predator Adaptations: cryptic

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: Hundreds of occurrences.

10,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but certainly exceeds 10,000.

Predators include birds and probably fishes.

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

Comments: Primarily nocturnal. Sometimes forages during the day.

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.

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.

Maximum longevity: 20 years (wild) Observations: While the average longevity of this animal is certainly much shorter, it has been suggested that dormant animals may have survived over 20 years in the arid Imperial Valley (http://www.fs.fed.us/database/feis/).

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.

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)

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.

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.

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.

The size of Great Basin spadefoot toads 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)

Breeds sporadically May-July, often after spring or summer rains. Eggs laid in small packets of 20-40 eggs. Female may lay a total of about 300-500 eggs. Under optimal conditions eggs probably hatch in about 2-3 days (Nussbaum et al. 1983). Larval period lasts a few to several weeks.

Year Assessed

Assessor/s

Reviewer/s

Justification

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

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Very narrow to narrow.

An explosive, opportunistic breeder, Spea intermontana is well adapted to the unpredictable and usually harsh seasons typical of the high desert areas it inhabits. Males have loud calls which attract females and probably other males to temporary or vernal pools where breeding takes place. Males are non-territorial, clumping and calling to females from partially submerged positions near the shore of pools. They appear to engage in a mad scramble for mates as they arrive. After breeding, adults disappear underground by using the spades on their hindfeet to burrow backward into the soil, thereby avoiding evaporative water loss to the dry desert air.

Eggs are laid underwater in groups of 10-40, and depending on the type of vegetation and substrate available, are arranged in either flat sheets, short strings, or golfball sized clusters.

Tadpoles may be either herbivorous or carnivorous, depending on local environmental conditions. The carnivorous morph has an enormous head, large jaw adductor muscles, and a sharp keratinous beak for tearing and cutting flesh. Tadpoles develop quickly to avoid dessication in their rapidly drying temporary pools.

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Area of occupancy and abundance are relatively stable.

Global Long Term Trend: Increase of 10-25% to decline of 30%

Comments: Likely relatively stable in extent of occurrence, likely less than 25 percent decline in population size, area of occurrence, and number/condition of occurrences.

Officially unthreatened, but recent studies have detected possible declines (Orchard 1992) and a repeat survey of historic collecting sites in the Sierra Nevada (Drost and Fellers 1996) found no specimens of Spea intermontana.

Major Threats

Comments: Most of habitat is not subject to incompatible uses or major threats, but intensive-extensive agriculture likely has extirpated/reduced some populations.

Conservation Actions

There are no known adverse effects of Spea intermontana on humans. 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.

Members of this species have few interactions with humans, positive or negative.