American Toad

Description

The American toad is a large, squat toad. Adults average between 5 and 9 cm in length. Females are generally larger than males, which are usually less than 8.5 cm long. Newly metamorphosed toadlets can be as small as 1 cm.

American toads are usually brown, tan or grey, but they can also have reddish, olive or dark brown skin. They have darker spots on their back that usually contain one or two wart-like bumps. This skin pattern can be used to differentiate American toads from Fowler's toads, the latter typically having more than two wart-like bumps within the spots on their back. A pale line can usually be seen running down the middle of the toad’s back. The belly of the American toad is white or cream-coloured with darker mottling. In the northern portions of their Canadian range, American toads are noticeably brighter than their southern counterparts, with a mottled pattern of contrasting colours, for example brick red, white, yellow and black.

Like other toads, American toads have rough, granular skin with wart-like bumps, large parotoid glands (kidney-shaped, poison-producing sacs behind each eye) and cranial crests (two bony ridges between the eyes). The tadpoles of the American toad have a long tail with a transparent fin. Young tadpoles are dark brown to black and become slightly less dark with brown, brass or gold specks as they age. Before metamorphosis, American toad tadpoles can grow to be up to 2.8 cm long.

Distribution and Habitat

In Canada, the American toad is found from Manitoba to Nova Scotia, and as far north as the Arctic coast of Labrador. They have also been introduced into parts of Newfoundland. The American toad can also be found throughout the Eastern United States, south to Georgia and west to North Dakota.

The American toad is a habitat generalist, meaning it can survive and thrive in diverse conditions. Like other toads, American toads have skin that is fairly resistant to dehydration compared to the majority of other amphibians. This allows them to spend most of their time on land as opposed to in water. However, despite the nature of their skin, American toads are nocturnal and require moist places to hide during the day. They can be found in forests, grasslands, urban environments and areas with sandy soil and exposed rock. They require shallow water to breed and will gather to do so in wetlands, ponds, lakes, flooded areas and even roadside ditches.

American toads usually hibernate underground in bedrock crevices, or in burrows that they dig themselves. This allows them to stay safely below the frost line for the duration of winter.

Reproduction and Development

American toads breed from late March to early June and may do so earlier in the southern reaches of their range or later in the northern reaches of their range. Male toads gather at a breeding site and call in a loud chorus to attract females. The call of the American toad is a single introductory note followed by a monotone trill that lasts from about 8 to 30 seconds. When in a breeding chorus, each male calls with a slightly different note.

Female toads lay between 2,000 and 20,000 eggs in two spiralling strands resembling strings of beads. These strings can be more than 60 m long and, as with most frogs and toads, are fertilized by the male as they are being laid. The eggs are dark above and lighter below and are surrounded by two clear jelly envelopes. The eggs hatch into tadpoles after 2–15 days.

American toad tadpoles metamorphose after five to ten weeks. It takes male American toads about two years to reach sexual maturity, while females can take three to four years. They live approximately six to seven years.

Diet and Predation

American toads forage for food primarily at night, although they may also be active on cloudy or rainy days. They eat anything they are able to capture. This includes insects, spiders, worms and slugs. Tadpoles feed on a variety of aquatic organisms, such as algae, organic debris and tiny aquatic animals.

Like all toads, American toads are poisonous and contain mildly toxic and foul-tasting substances that deter most predators. These substances can irritate mucous membranes in humans and can cause sickness if eaten by smaller animals such as dogs, although this is rare due to the noxious taste. Some predators, however, are not deterred by the American toad’s poison. Raccoons, skunks, certain snakes and birds are all known to be predators of adult American toads. Some species, such as the Eastern hog-nosed snake, even specialize in hunting toads. Species that prey on American toad tadpoles include invertebrates and other species of amphibians.

Status and Threats

The Committee on the Status of Endangered Wildlife in Canada has not assessed the American toad. Internationally, it has been categorized as “least concern” by the International Union for Conservation of Nature.

American toads are better able to tolerate human disturbances compared to many other amphibians. This is because they are habitat generalists and are often able to adapt to changing conditions, or else travel to new locations when necessary. However, extreme habitat loss and fragmentation, especially the loss of breeding ponds, can lead to local extirpation.

American toads are also negatively affected by other threats, such as pollution, road mortality and disease. Pollutants such as road salt and pesticides can lead to direct mortality and severe developmental deformities. Pathogens such as the Ranavirus are known to have caused mass mortality events among amphibian populations.