American Toad – Bufo americanus

General: The American Toad (Bufo americanus) is a common inhabitant of The American toad (Bufo americanus) is a common species of toad found throughout the eastern United States and Canadagardens and shady backyard spaces across much of North America. These amphibians are often identified first by their musical trills, heard on warm nights in the spring and fall. Stout and stubby in appearance, it is comical to watch an American Toad lumbering across organic debris and vegetation. American Toads have the greatest geographic range of all toad species in North America and have no special conservation designation.

Description: American Toads are rotund amphibians that reach an adult size of 2” to 4.5” long, females usually reaching a greater overall size than males. They are often described as chubby and stout, with short limbs, wide heads, and muscular hind legs. The front legs have four toes, while the back legs have five webbed toes. American Toads have black ovular pupils often circled with gold and prominent cranial ridges with lateral branches that extend behind the eyes1. The cranial crests occur in front of two large parotid glands, which may be identified by their bean-shape, that are capable of producing a foul smelling chemical used to ward off predators. Their thick, rough skin ranges from brown, gray, brick red or olive in color and is accented by noticeable warts. These warts, which are yellow or brown, appear singly or in pairs and are contained within large brown or black spots across the back. These spots may be circled by yellow or white. Some toads have patterns of light, yellow, or buff on their bodies, which may create a light ‘stripe’ down the back. Males and females have white or yellow undersides with dark speckling, but males often display a darker throat that is black or brown2. The skin of American Toads may change color due to temperature, time of day, humidity, stress, age or sex. American Toads shed their external skin four times a year. The skin is sloughed off in one piece and then consumed by the toad. Immature American Toads shed their skin every few weeks3.

Two subspecies of the American Toad exist. Dwarf American Toads, Bufo americanus charlesmithi, are typically found in western parts of the geographic range and can be identified by their smaller size (adults reaching only 2.5” in length,) dark red coloration, and fewer or no spots on their backs (spots that are present contain one wart, at most.) The Eastern American Toad, Bufo americanus americanus, inhabits the eastern portions of the range and is medium in size (reaching lengths of 3.5”,) has variable coloration, has one to two warts contained within each spot, enlarged warts on the lower legs, and speckling only on the front half of the belly4. American Toads are often confused with Fowler’s Toads because of their similar appearances. However, where the American Toad only has one or two warts in each spot, a Fowler’s Toad has several warts in each spot on its back.

American Toads produce a high-pitched trill, most often heard during the early spring (when calling mates,) or in the fall (when locating a hibernation area,) that is held for 4 to 30 seconds. Males produce this call by inflating their round vocal sac, called the dewlap, and use it to attract females during the breeding season. At the height of the season calls can sound frantic and loud as males compete for mates. In addition to their recognizable calls, American Toads also use touch, chemical cues and posture to communicate5. In response to predators, American Toads may release a toxic chemical from their parotid glands, play dead or puff-up their bodies to appear larger.

American Toads are nocturnal and are most active during warm and humid weather. During the day they tend to burrow into soil or leaf litter, or under rocks or logs6. They are also a solitary species, only social when at breeding ponds during the mating season. During the winter, American Toads burrow into soil below the frost line, continuing to burrow further as the frost deepens.

In captivity American Toads have been known to live to over 30 years old. However, in the wild, many tadpoles perish before completing their complete metamorphosis into mature toads. Adult toads live, on average, a couple years in the wild but have been known to live as long as ten years.

Habitat: American Toads are a highly adaptable species and can be found in a variety of habitats. Preference changes seasonally but American Toads generally require some source of moisture, vegetation for burrowing and hunting, and a constant supply of food.

During the breeding season, American Toads inhabit areas that provide a body of freshwater that is either temporary or permanent. These areas include wetlands, temporary pools, shallow bays, swamps, streams, and ditches. These freshwater bodies are used for mating and depositing eggs as well as throughout the early development of tadpoles.

After the spring breeding season, American Toads are able to move further from water sources and can be found in forests, meadows, woodlands, shady suburban yards, grasslands, gardens, farmlands, and prairies. Their muscular hind legs make it possible to move amongst the leaf litter and debris on the ground.

During winter hibernation, American Toads burrow into the ground, remaining below the frost line.

Predators of the American Toad include snakes, skunks, owls and raccoons, although predators are often deterred by the toxic chemicals released by the parotid glands and the bitter tasting skin. Raccoons have adapted to this occurrence by eating from the undersides of toads, far from the chemical producing glands.

Location: American Toads are found across most of North America (except for most southern states) since they are a highly adaptable species that only requires seasonal water for breeding7.

Diet: American Toads are carnivores, consuming a massive quantity –up to 1000 insects a day- of insects, spiders, snails, slugs, and worms. They catch prey by thrusting out their sticky tongues and using their forearms to hold large prey and pack it into their mouths. While American Toads do not drink water, they are able to absorb moisture from their environments through their thick, rough skin.

Tadpoles are herbivorous, consuming aquatic vegetation along the edges of their freshwater habitats.

Reproduction: American Toads are polygamous and mate once annually, typically between April and July. Breeding activity is triggered by the rising temperatures and lengthening days of spring. Male toads arrive at breeding ponds before females in order to establish territories. These congregations of males produce their signature calls to attract females, who select mates based on the quality of their calls and breeding territories8.

Males grasp the larger females from behind during egg deposit and fertilization in a position called amplexus. Females lay between 4000 to 8000 1.5mm counter-shaded eggs (white on the bottom and black on the top for camouflage,) within long tubes of jelly attached to submerged vegetation. Females provide nutrients to the eggs internally but males and females provide no parental care past egg fertilization and deposit. Females prefer breeding ponds without fish to ensure greater survival rates for their offspring. The eggs will hatch in 3 to 12 days, with maturation rates depending on environmental temperatures9.

The tiny tadpoles hatch with rounded tails and bodies, gills on the sides of their heads, and smooth black skin, which emits defensive chemicals (similar to adults) for defense. Tadpoles swim in schools and consume plant matter that will fuel their steady growth into mature toads. For 50 to 60 days following hatching, tadpoles go through a process called metamorphosis, in which they transform into miniature versions of mature toads. Over the first 20 days, tadpoles develop hind legs. The front legs develop between 30 and 40 days old, emerging from underneath a layer of skin. During this period, tadpoles begin breathing air as their gills disappear. Over the last few days of metamorphosis, tadpoles reabsorb their tales and begin eating animal matter10. Tadpoles reach a length of just over a centimeter before transforming into toadlets, or small versions of fully mature toads that are between .8cm and 1.3cm in length11. These young toads remain in close proximity to the breeding pond for several days after completing metamorphosis and then move into terrestrial habitats12. American Toads reach sexual maturity in two to three years.

Notes of Interest: Despite popular belief, humans cannot get warts from touching a toad. It is, however, advisable to use caution when handling these creatures because the chemicals released from the parotid glands can cause irritation if they are consumed or come in contact with your skin or eyes.

Footnotes
1. http://www.uri.edu/cels/nrs/paton/LH_ea_toad.html
2. http://www.fcps.edu/islandcreekes/ecology/american_toad.htm
3. http://www.biokids.umich.edu/critters/Bufo_americanus/
4. http://www.npwrc.usgs.gov/resource/herps/amphibid/species/american.htm
5. http://www.biokids.umich.edu/critters/Bufo_americanus/
6. http://www.biokids.umich.edu/critters/Bufo_americanus/
7. http://www.biokids.umich.edu/critters/Bufo_americanus/
8. http://www.biokids.umich.edu/critters/Bufo_americanus/
9. http://www.biokids.umich.edu/critters/Bufo_americanus/
10. http://www.biokids.umich.edu/critters/Bufo_americanus/
11. http://www.biokids.umich.edu/critters/Bufo_americanus/
12. http://www.biokids.umich.edu/critters/Bufo_americanus/

http://www.fcps.edu/islandcreekes/ecology/american_toad.htm
http://www.dnr.state.mn.us/reptiles_amphibians/frogs_toads/toads/american.html
http://www.dnr.state.oh.us/tabid/6602/Default.aspx
http://www.biokids.umich.edu/critters/Bufo_americanus/
http://www.uri.edu/cels/nrs/paton/LH_ea_toad.html
http://www.npwrc.usgs.gov/resource/herps/amphibid/species/american.htm

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