Bufo americanus (American toad)

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Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Sarcopterygii - Tetrapoda - Amphibia - Batrachia - Anura - Neobatrachia - Hyloidea - Bufonidae - Bufo - Anaxyrus - Bufo americanus

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Brief facts

• Distribution

  American toads occur in most of the eastern half of the United States and southern Canada. They are generally not present in the most southern states or, if they are, only in the northern part. Populations of B. americanus and B. fowleri often overlap and interspecies hybridization was documented.

• Physical description

  The skin color of adult American toads is normally brown to gray with several darker spots on the back, typically with 1-2 warts per spot (as compared to 3-5 warts per spot in Fowler's toads). The bellies are a white or yellow. In American toads, the paratoid glands do not touch the cranial crest (located directly behind the eyes). Adult toads photos (new window). Tadpoles are round, almost black with somewhat long snout; large specimens may have coppery iridophores. Tadpoles photos (new window).

• Habitat

  Adult toads are terrestrial. They can occupy a variety of habitats ranging from forests to backyards. They are common in gardens and agricultural fields. During daylight hours they seek cover beneath porches, under boardwalks, logs, wood piles, or in dense vegetation. At dusk and at night, they come out for hunting. Often they can be found on roads near source of light that attracts insects. In cold season, these toads hibernate in burrows. Unlike some other amphibians they are not freeze-tolerant and finding site where temperatures won't fall below freezing point is crucial for their survival.

• Food habits

  American toads eat a wide variety of invertebrates, including snails, beetles, slugs, and earthworms. Tadpoles are herbivorous, detritovorous, necrophagous, and cannibalistic.

• Antipredator strategies

  Adult toads are protected from vertebrate predators by the presence of noxious and toxic skin secretions produced and stored in glandular glands of the skin. This toxin is secondarily deposited in the ova, and protects embryos until hatching from leeches (Batrachobdella spp.), salamander larvae (Ambystoma gracile), and fish. However, on later stages of development on stages 31-41, tadpoles loose this initial protection and become palatable to the aquatic predators frequently falling prey to fish and predaceous invertebrates such as larvae of diving beetle Dytiscus verticalis and nymphs of the giant water bug Lethocerus americanus. Metamorphosing tadpoles are clumsy, their ability to escape by swimming away is greatly impaired. To reduce losses from predation at these stages toads use two strategies: firstly, they become repulsive to predators due to developing noxious glands; and, secondly, late stages of metamorphosis progress very rapidly and are completed withing 2-3 days. Newly metamorphosed and adult toads exhibit cryptic behavior. They respond to predators by crouching and immobility (even when prodded they initially resist temptation to move away). They usually become immobile immediately after contact with predator or upon being seized. This often results in a non-capture or a subsequent release without injury. Immobility reduces the intensity of predator's attack and may prevent killing of the toad by the predator who normally would not eat the repulsive toad. Also, toads seek substrates on which they are less conspicuous and can change their skin color (darken or lighten) depending on the shade of the substrate. Photos of toad captured by a garter snake (new window).

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American toad diary (Maryland)

Year	Mating	Dispersal
2010	April 4	May 26-29
2011	April 15	June 12-15
2012	March 17	?
2013	April 10	?

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References

• Gosner KL. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183-190.
• Gatz AJ. 1975. Non-random mating by size in American toads, Bufo americanus. Herpetologica 31:222-233.
• Beiswenger RE. Non-random mating by size in American toads, Bufo americanus. Anim. Behav., 1981, 29, 1004-1012.
• Heinen JT. 1994. Antipredator behavior of newly metamorphosed American Toads (Bufo a. americanus), and mechanisms of hunting by eastern garter snakes (Thamnophis s. sirtalis). Herpetologica. Vol. 50, No. 2 (Jun.,1994), pp. 137-145.
• Heinen JT. 1994. Significance of color change in newly metamorphosed American toads (Bufo a. americanus). J. of Herpetology, Vol. 28, No. 1 (Mar.,1994), pp. 87-93.
• Sontag C et al. Social foraging in Bufo americanus tadpoles. Anim. Behav., 2006, 72, 1451-1456.
• Formanowicz DR, Jr. and Brodie ED, Jr. Relative palpatabilities of members of larval amphibian community. Copeia, Vol. 1982, No. 1 (Feb. 23,1982), pp. 91-97.
• Howard RD & Young JR. Individual variation in male vocal traits and female mating preferences in Bufo americanus. Anim. Behav., 1998, 55, 1165-1179.
• Brodie ED, Jr et al. The development of noxiousness of Bufo americanus tadpoles to aquatic insect predators. Herpetologica. Vol. 34, No. 3 (Sep.,1978), pp. 302-306.
• Nityananda V, Bee MA. Finding your mate at a cocktail party: frequency separation promotes auditory stream segregation of concurrent voices in multi-species frog choruses. PLoS One. 2011;6(6):e21191.
• Harper EB, Semlitsch RD. Density dependence in the terrestrial life history stage of two anurans. Oecologia. 2007 Oct;153(4):879-89.

Websites and other references

• Grossman, S. 2002. "Bufo americanus" (On-line), Animal Diversity Web. Accessed April 25, 2010 at Animal Diversity Web (ADW).
• Amphibians of Maryland (Twoson University, Biological Sciences)
• Tadpoles of the United States and Canada: A Tutorial and Key
• An Online Guide for the Identification of Amphibians in North America north of Mexico

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