|
Canadian Herpetological Society Société d'Herpétologie du Canada |
|---|
American Toad
Anaxyrus americanus
Family: Bufonidae
Until recently, the American Toad was in the genus Bufo, but it is now in the genus Anaxyrus.
COSEWIC status:- Not Assessed
- No Status
- Least Concern
Description
The American Toad is a medium to large toad that can grow to over 11 cm in body length; however, females grow much larger than males, which rarely exceed 8.5 cm in body length. Individuals are typically brown, tan or grey but are sometimes red, orange, olive brown or dark brown, and they have small dark spots on the back that each contain one or two large wart-like bumps. The belly is white or cream-coloured with grey mottling. American Toads have granular skin with large wart-like bumps, a large, kidney-shaped parotoid gland behind each eye, and pronounced cranial crests (two raised ridges between the eyes) that are furthest apart at the back of the head. The legs are short and the hind feet have moderate webbing between the toes. Larvae (tadpoles) have long tails with a large fin and lack front legs (newly hatched tadpoles are legless). Young larvae are black with a clear tail fin, but they become slightly less dark and gain brown, brass or golden flecking as they age. The larvae can grow up to 2.8 cm in total length before metamorphosis. The call is a long, high-pitched trill.
Similar Species
The American Toad can be confused with the Fowler’s Toad and Canadian Toad. The Fowler’s Toad, which has a Canadian distribution that is limited to a few sites along the north shore of Lake Erie, typically has three or more wart-like bumps in each dark blotch on its back and plain, a light-coloured belly, while the American Toad has one or sometimes two bumps per blotch and dark mottling on the belly. The range of the American Toad only overlaps with the Canadian Toad in southeastern Manitoba and the species interbreed in this area, making identification of some individuals difficult. The cranial crest of the Canadian Toad are more-or-less parallel and they connect at the back of the head to form an obvious bump (called a boss), whereas the American Toad’s cranial crests diverge at the back of the head and form a “V” shape.
Distribution
Click for larger image
The American Toad has a widespread distribution in Canada, ranging from eastern Manitoba east to Nova Scotia, Prince Edward Island and Newfoundland and Labrador and encompassing almost all of eastern Canada except for the extreme northern tip of Ontario, northern Quebec and parts of Newfoundland and Labrador. This species also occurs throughout most the eastern U.S., extending from North Dakota east to Maine and as far south as Georgia and northeastern Texas.
Habitat
American Toads breed in a diversity of permanent or temporary shallow aquatic features, including marshes, bogs, fens, swamps, vernal pools, ponds, flooded areas, and sheltered bays of lakes or backwaters of small streams. American Toads are habitat generalists and can be found in a wide range of terrestrial habitats outside of the breeding season, including deciduous and mixed forests, forest clearings, grasslands, meadows, old fields, and rock barrens. Individuals hibernate below the frost line in burrows that they excavate in sandy soils, mammal burrows, crevices in bedrock and other underground cavities.
Biology
In Canada, American Toads hibernate during the winter and are active from April or early May until late September or October, depending on latitude. Males call to attract females during the breeding season, which occurs over a 1–2 week period from April to June in Canada, 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 2,000–15,000 eggs in two long strings that can be over 60 m in length. The eggs are black on top and somewhat cream-coloured underneath and are surrounded by two clear jelly envelopes. The eggs develop rapidly and hatch in 2–7 days, depending on water temperature, and the tadpoles transform into juvenile frogs after 6–9 weeks. Males reach sexual maturity at 2 years of age, while females may not mature until they reach 3 or even 4 years of age. American Toads can live to be 6 or 7 years old. American Toads are primarily nocturnal and they spend much of the day seeking shelter under logs, rocks or other cover objects. Individuals forage for almost anything they can capture, eating a wide variety of invertebrates, such as insects, spiders, slugs and snails. 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. American Toads can tolerate dry conditions and are often found considerable distances from water. Individuals often return to the same breeding site in successive years, and they may travel several kilometers between breeding sites, summer habitats and hibernation sites.
Threats
American 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. Pollution, such as herbicides and road salt, 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 may also pose future threats to Canada’s frog and toad populations.