American Toad

Anaxyrus americanus

Physical Description

A large, stout bodied toad averaging 5.0-9.5 cm (2.0-3.7 in.) SVL. Generally tan, brown, olive, or red in color, while the ventral surface is predominately cream-colored with light mottling. Dark brown dorsal spots usually contain only 1 or 2 large warts. Prominent paratoid gland found behind each eye and not touching cranial ridges, or only by a short spur[1]. Adult American Toads are sexually dimorphic: Females are the larger sex and generally much redder in appearance, while males are duller colored, smaller, have black throats, and nuptial pads on their thumbs.

Vocalization

Male American Toads have a long, melodic trill emitting from a single vocal sac. Calls last up to 30 seconds.

Habitat

Breeding habitat

Permanent and temporary water sources, including ponds, lakes with shallow margins, wetlands and slow-moving stream sections. American Toads can also be found breeding in flooded fields, ditches, and ornamental ponds.

Non-breeding habitat

American Toads are thought to be habitat generalists, found in deciduous, coniferous, or mixed forests. American Toads are commonly found in urbanized landscapes as well and are frequently observed foraging under streetlamps.

Geographic Distribution

Canadian maritime provinces to southeast Manitoba, south to North Carolina and Mississippi[2].

Reproduction and Juvenile Growth

Adult American Toads breed shortly after emerging from winter dormancy between February and June, depending on climatic conditions of the region. Males migrate to breeding sites shortly before the females and calling males establish territories while others swim about actively searching for arriving females. Terrestrial amplexus is common in American Toads, in which females are intercepted by one or more males and must carry these suitors to the water source[3]. Once females arrive at the breeding sites they are oftentimes subjected to intense male competition, called “mating balls”, where amplexed individuals attempt to displace other males, occasionally resulting in the death of the female. Amplexus and oviposition can last for several hours and occurs in the shallow margins of the breeding site, where females lay two long strings of eggs encapsulated in a protective gelatinous coating. Fecundity is strongly correlated to female body size, with typical clutch sizes of 2000-15,000 ova which are each 1.0-1.5 mm in diameter (pers. obs.).

Eggs hatch into free-swimming tadpoles within 3-21 days with hatching time being largely dependent on water temperature. Tadpoles take an additional 30-60 days to develop and metamorphose. Larval developmental period is also dependent on a number of factors, including water quality, food availability, the presence of predators, and the density of competitors. Recently metamorphosed American Toads superficially resemble miniature adults; averaging 0.7-1 mm SVL and weighing 70-200 mg (pers. obs.). Juveniles reach sexual maturity 2-4 yrs after metamorphosis.

Diet

Adult American Toads feed primarily on insects, including ground beetles (Coleoptera: Carabidae) and shield bugs (Hemiptera: Pentatomidae; pers. obs.). Adults are also known to prey on spiders, millipedes, ants, and orthopterans. Tadpoles primarily forage on detritus but will opportunistically feed on deceased conspecifics if natural food sources are limiting.

Predators and Defenses

American Toads have conspicuous paratoid glands on their dorsum which, when provoked, secrete a milky substance called bufotoxin. These secretions are unpalatable to many animals and may even cause death in some animals[4].

Herons, raptors, snakes (including hognose and garter snakes), snapping turtles, and mammals prey on adult American Toads. Egg and tadpole stages are preyed on by numerous species of larval ranids, including wood frogs, green frogs, and bullfrogs, as well as larval ambystomid salamanders and adult Notophthalmus newts.

Taxonomic notes

There are currently two recognized subspecies of the American Toad: Eastern American Toad (A. a. americanus) and Dwarf American Toads (A. a. charlesmithi). Dwarf American Toads have a much more restricted range, only occupying the southwestern extent of the species range[2]. As the name implies, Dwarf American Toads are smaller (< 6.0 cm SVL) than Eastern American Toads. They are also redder in color and contain fewer warts.

Etymology

Anaxyrus: (Greek) – A king or chief.

americanus: "America", referring to the widespread distribution of this species throughout North America

Subspecies americanus: "America", referring to the widespread distribution of this subspecies.

Subspecies charlesmithi: Homage to the naturalist Charles C. Smith.

References

  1. White, JF, and AW White. 2007. Amphibians and Reptiles of Delmarva. Tidewater Publishers, Centerville, MD.
  2. Conant, R. and J. T. Collins. Reptiles and Amphibians: Eastern/Central North America. Houghton Mifflin Co., Boston
  3. Forester, D. C. and K. J. Thompson. 1998. Gauntlet Behaviour as a Male Sexual Tactic in the American Toad (Amphibia: Bufonidae). Behaviour 135: 99-119
  4. Barbosa C. M., M. S. Medeiros, C. C. M. Riani Costa, A. C. Camplesi, and M. Sakate. 2009. Toad poisoning in three dogs: Case reports. Journal of Venomous Animal Toxins including Tropical Diseases 15: 789-798

Classification

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