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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Great Basin Spadefoot
Spea intermontana
Family: Scaphiopodidae
COSEWIC status:- Threatened
- Threatened
- Least Concern
Description
The Great Basin Spadefoot can attain a body length of up to 6.5 cm. Individuals are tan, grey or olive with dark reddish brown spots and sometimes have two light lines that run down the back and form an hourglass shape. The colouration often matches the substrates of the areas in which they are found. The eyes are golden yellow with vertical pupils, and the belly is white to cream-coloured. Individuals have relatively smooth skin covered with tubercles (small bumps), upturned eyes, a bump (called a boss) between the eyes, a blunt snout that is slightly upturned, short legs, webbed feet and a black ridge (spade) on the bottom of each hind foot that is used for burrowing. Larvae (tadpoles) have long tails with a large tail fin, a triangular-shaped head, upturned eyes that are located high on the head, and lack front legs (newly hatched tadpoles are legless). The larvae’s body is grey, brown or black with gold or brassy flecking, the belly is golden-tinged and there is dark flecking on the tail. The larvae can reach 7 cm in length before metamorphosis. The call of Great Basin Spadefoot is a series of rapid, low-pitched, guttural sounds.
Similar Species
The Great Basin Spadefoot may be confused with the Western Toad. The Western Toad has bumpier skin, horizontal pupils and large parotoid glands behind the eyes, and it lacks the “spade” on the hind feet.
Distribution
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The Great Basin Spadefoot is found in the dry southern interior of British Columbia in the Okanagan Valley and the Nicola, north Thompson and Similkameen River valleys. This species’ distribution extends south to southern California on the east side of the Coast Mountains and east to central Wyoming.
Habitat
This species is found in semi-arid habitats, such as dry grasslands, open woodlands and sagebrush plains. The Great Basin Spadefoot breeds in permanent or temporary wetlands, the shallow margins of lakes or streams, pools, springs and other shallow aquatic features. Individuals require loose, sandy soils in which they can burrow to seek shelter during the day and during extended dry periods. They hibernate underground below the frost line in deep burrows that they excavate or in mammal burrows.
Biology
n Canada, individuals hibernate during the winter and are active from early April until October. Male Great Basin Spadefoots call to attract females during the breeding season, which occurs over a few weeks from late April to early June. During breeding, the male grasps the female (amplexus) and fertilization occurs externally in aquatic habitats as the female lays eggs. The female lays 300–1000 eggs in small clumps of 20–40 eggs, which are usually attached to vegetation or other debris in shallow water. The eggs are black on top and creamy white underneath and are surrounded by clear jelly envelopes. The eggs develop rapidly and hatch in 2–7 days, and larvae transform into juveniles after 4–8 weeks. Great Basin Spadefoots reach maturity at 2–3 years of age and can likely live for over 10 years. Adults and juveniles are primarily nocturnal and forage for a wide variety of invertebrates, including worms, beetles, flies, ants and grasshoppers. Larvae can be omnivorous or carnivorous, each having different mouth morphology (i.e. carnivorous larvae have a sharp “beak”). Spadefoots are highly resistant to desiccation and can tolerate high levels of water loss. They also burrow underground and become dormant during extended dry periods, where they can absorb water directly from the soil in their burrows. Spadefoots secrete a noxious substance from their skin when threatened to deter predators.
Threats
Great Basin Spadefoots occur in a heavily developed region of Canada and habitat loss and fragmentation, primarily from urban expansion and agricultural activities, is the most significant threat to this species. Drawing water for irrigation or other activities that lower the water table, the introduction of predatory sports fish, as well as cattle grazing can render breeding habitats unsuitable. Roads pose a serious threat to this species and can cause high rates of mortality during mass migrations when they bisect travel corridors. Pesticides/herbicides, road salt and other environmental pollutants can be detrimental to frog and toad populations by causing direct mortality as well as developmental deformities. Pathogens, such as chytrid fungus and Ranavirus, can cause mass mortality of frog and toad populations. Climate change may also pose future threats to the Great Basin Spadefoot, particularly by increasing the frequency and severity of droughts.