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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Great Plains Toad
Anaxyrus cognatus
Family: Bufonidae
Until recently, the Great Plains Toad was in the genus Bufo, but it is now in the genus Anaxyrus.
COSEWIC status:- Special Concern
- Special Concern
- Least Concern
Description
The Great Plains Toad is a medium to large toad that can grow up to 11 cm in body length, with females being slightly larger than males. Individuals are typically light brown, grey or olive with large, light-bordered dark blotches and a light-coloured stripe running down the back, though the vertebral stripe is often absent on lighter-coloured individuals. The belly is usually solid white. Great Plains Toads have granular skin with small wart-like bumps, a large, kidney-shaped parotoid gland behind each eye, and pronounced “L”-shaped cranial crests (two raised ridges between the eyes) that are furthest apart at the back of the head. The legs are short and there are two dark tubercles on the hind feet that are used for burrowing. Males can be differentiated from females by their dark throat. Larvae (tadpoles) have long tails with large, highly arched tail fins and they lack front legs (newly hatched tadpoles are legless). Young larvae are black with a lighter belly, but they become gray and mottled brown with silver flecking as they age. The larvae can grow up to 3 cm in total length before metamorphosis. The call is a long, loud, metallic-sounding trill.
Similar Species
The Great Plains Toad can be confused with most other toad species in Canada, as well as the Plains Spadefoot. Its distribution does not overlap with that of the Fowler’s Toad, American Toad and Western Toad in Canada, although it does occur in close proximity to the latter two. The cranial crests of the Great Plains Toad diverge at the back of the head to form a “V” shape, while the cranial crests of the Canadian Toad are parallel and connect at the back of the head to from a prominent bump (boss). The Western Toad lacks cranial crests altogether. The cranial crests of the Great Plains Toad and the American Toad are similar, but the Great Plains Toad has large dark blotches with many small warts while the American Toad has smaller dark blotches with 1–2 warts per blotch. The Plains Spadefoot lacks cranial crests and parotoid glands and has vertical pupils.
Distribution
Click for larger image
The Great Plains Toad has a small distribution in central Canada, ranging from southeastern Alberta through southern Saskatchewan and into extreme southwestern Manitoba. This species occurs throughout the central U.S. Great Plains states from Montana, North Dakota and western Iowa south to southeastern California and western Texas, and into northern Mexico.
Habitat
Great Plains Toads inhabit the dry grasslands of the southern prairie region of Canada. This species breeds in shallow, temporary pools created by snow-melt and rainwater, as well as anthropogenic features such as waterfowl ponds, dikes, ditches and flooded fields. Individuals burrow into loose soil to seek refuge from the heat during the day and during extended dry periods, and they dig deeper burrows that extend below the frost line for hibernation.
Biology
In Canada, Great Plains Toads hibernate during the winter and are active from April until October. Males call to attract females during the breeding season, which typically occurs in May or June. However, breeding is often triggered by rainfall and may occur later in the season in years when spring rainfall is low. Breeding is explosive and often occurs over a very short period when conditions are suitable. During breeding, the male grasps the female (amplexus) and fertilization occurs externally in aquatic habitats as the female lays eggs. The female lays 1,300–45,000 eggs in two long strings. The eggs are black on top and lighter-coloured underneath, are surrounded by two clear jelly envelopes and are enclosed in long, tough gelatinous strings. The eggs develop rapidly and hatch in 2–7 days and the tadpoles transform into juvenile frogs after 2.5–7 weeks, with both rates of development being dependent on temperature. In Canada, males reach sexual maturity at 2–3 years of age, while females mature at 3–4 years of age. Great Plains Toads may live for more than 10 years, though most individuals do not live this long. Great Plains Toads are primarily nocturnal and they spend much of the day seeking shelter from the heat. Individuals forage for almost anything they can capture, eating a wide variety of invertebrates, particularly beetles and ants. Toxins and noxious secretions that deter predators are produced by glands in the toad’s skin, particularly in the parotoid glands and the wart-like bumps. Individuals are dehydration-tolerant and will remain relatively inactive underground for extended periods during extreme drought. Great Plains Toads have large home ranges and can travel over a kilometre between breeding sites, summer habitats and hibernation sites.
Threats
The extensive conversion of prairie grasslands to agricultural uses has resulted in widespread habitat loss and continues to pose a significant threat to this species in Canada. Herbicides/pesticides, road salt and other environmental contamination can be detrimental to frog and toad populations by causing direct mortality as well as developmental deformities. Road mortality can be a significant threat when roads bisect the species’ habitat. Pathogens, such as chytrid fungus and Ranavirus, can cause mass mortality of frog and toad populations. Climate change also poses a threat to this species, particularly by increasing the frequency and severity of droughts.