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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Canadian Toad
Anaxyrus hemiophrys
Family: Bufonidae
Until recently, the Canadian Toad was in the genus Bufo, but it is now in the genus Anaxyrus.
COSEWIC status:- Not at Risk
- No Status
- Least Concern
Description
The Canadian Toad is a medium-sized toad and can grow to 9 cm in body length, with males being slightly smaller than females. Individuals are tan, light brown, grey, brownish green or reddish brown with darker blotches. There is usually a white or cream-coloured vertebral stripe that runs down the back, though it can be faded on some individuals. The belly is white to tan with grey spotting. Canadian Toads have granular skin with large wart-like bumps, a large, kidney-shaped parotoid gland behind each eye, and pronounced cranial crests (raised ridges between the eyes). The legs are short and there are two prominent tubercles on the hind feet that are used for burrowing. Larvae (tadpoles) have long tails with a large fin and lack front legs (newly hatched tadpoles are legless). The larvae are black with a bi-coloured tail and clear tail fins. The larvae can grow up to 3 cm in total length before metamorphosis. The breeding call is a high-pitched trill.
Similar Species
The Canadian Toad can be confused with the American Toad, Great Plains Toad, Western Toad and Plains Spadefoot. However, the Canadian toad is the only species with cranial crests that connect at the back of the head to from a prominent bump (boss). The Western Toad lacks cranial crests, and the cranial crests of the American Toad and Great Plains Toad diverge at the back of the head and form a “V” shape. The range of the American Toad overlaps with the Canadian Toad in southeastern Manitoba and the species interbreed in this area, making identification of some individuals difficult. The Plains Spadefoot lacks cranial crests and parotoid glands and has vertical pupils.
Distribution
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As the name implies, the majority of the Canadian Toad’s distribution occurs in Canada. It is found throughout eastern Alberta, a small part of the southern Northwest Territories, most of Saskatchewan with the exception of the northeastern portion of the province, and southwestern Manitoba. In the United States, this species is restricted to North Dakota, eastern South Dakota and western Minnesota.
Habitat
Canadian Toads breed in a variety of shallow aquatic habitats, such as the margins of lakes, ponds, wetlands, slow-flowing portions of streams and rivers, and ditches. Breeding sites are located in open habitats, such as prairie and aspen parkland, rather than in forested areas. During the summer, Canadian Toads disperse into terrestrial habitats, such as prairie and grassland, aspen parkland, woodland, and willow or grassy bogs, but they generally remain close to water. Individuals hibernate underground below the frost line in burrows that they excavate.
Biology
In Canada, Canadian Toads hibernate for much of the year and are only active from May until early September. Males call to attract females during the breeding season, which occurs in May to early July, depending on latitude. During breeding, the male grasps the female (amplexus) and fertilization occurs externally in aquatic habitats as the female lays eggs. The female lays 3,000–6,000 eggs in two long strings. The eggs develop rapidly and hatch in 2–7 days and the tadpoles transform into juvenile frogs after 6–8 weeks, depending on water temperature. Males reach sexual maturity 1–3 years after metamorphosis, while females mature at 3–4 years of age. Canadian Toads can live to up to 12 years of age, but most only live a few years. Individuals forage for a variety of insects, primarily ants and beetles, as well as spiders and other invertebrates. Toxins that deter predators are produced by glands in the toad’s skin, particularly in the parotoid glands and the wart-like bumps. Canadian Toads are less tolerant of dry conditions than other toads and they are typically found close to water or in moist environments.
Threats
Canadian Toads occur throughout large expanses of Canada that are relatively undeveloped, and threats to this species are minimal throughout most of its range. Habitat destruction, particularly the loss of breeding ponds, can result in population declines or local extirpation. 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. 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.