Description

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Anaxyrus americanus has a short, stout body, with a short broad head bearing large parotoid glands and having a broadly circular snout. The back is covered with different-sized warts and the venter is granular. There are three or four pairs of dark spots down the back, each accompanied by one large wart. Eyes are prominent. The arms and legs are tubular and warty. They are generally olive in color, with a brown crest (Wright and Wright 1949).

Males are roughly 54-85 mm in length. The back, sides and tympana are a dull citrine color with olive-citrine or yellow olive color on their hind legs and forelegs. The pectoral region is covered with scattered black spots, and these spots occur over the entire venter except for the throat and the center of the posterior venter. There is some apricot-yellow color across the arm insertion. The pupil is rimmed with citron yellow (Wright and Wright 1949).

Females are roughly 56-110 mm in length. The back is a light brownish or buffy olive. The bigger warts are on the back, and the warts are in the centers of buffy brown colored spots. There is a stripe down the middle of the back, of a deep-olive buff color, yellow, or vinaceous-fawn, that leads from parotoid to groin. In the center of the breast, there is a dark spot (Wright and Wright 1949).

References

  • Cook, F. R. (). Introduction to Canadian Amphibians and Reptiles. National Museums of Canada, Ottawa, Canada.
  • Johnson, T. R. (). The Amphibians and Reptiles of Missouri. Missouri Department of Conservation, Jefferson City.
  • Oliver, J. A. (). The Natural History of North American Amphibians and Reptiles. D. Van Nostrand Campany, Ltd., Canada.
  • Schmidt, K. P. (). A Checklist of North American Amphibians and Reptiles. The University of Chicago Press, Chicago, Illinois.
  • Wright, A. H. and Wright, A. A. (). Handbook of Frogs and Toads of the United States and Canada. Comstock Publishing Company, Inc., Ithaca, New York.

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Distribution and Habitat

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Anaxyrus americanus can be found in Eastern North American, from the maritime provinces of Quebec and Ontario in Canada to Minnesota. Its range spans from the northern borders of the Gulf States, excluding Louisiana, and Texas. They can also be found in Arkansas, eastern Oaklahoma, and eastern Kansas (Schmidt 1953). Within Canada, A. americanus can be found in Ungava, James Bay, and sometimes the coast of Hudson Bay. It also occurs from Prince Edward Island to East Manitoba, and has been introduced to parts of Newfoundland (Cook 1984).

During the periods where the toads are not reproducing, they live in within an area of approximately 100' x 100'. However, during the breeding period, they may move several thousand feet away.

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Life History, Abundance, Activity, and Special Behaviors

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Anaxyrus americanus lays its eggs between the months of April to July (Oliver 1955). The peak of the breeding season is usually late April (Wright and Wright 1949). Breeding sites are usually small ditches, small ponds, or slow, shallow streams (Johnson 1987). The male grasps the female behind her front legs, and she will begin laying her eggs (Johnson 1987).

Clutch size is usually 4,000-8,000 eggs, in a single string. The eggs will incubate for about 3-12 days before hatching. The tadpoles are dark, almost black. After the young toads metamorphose, they will migrate in mass numbers away from the water (Wright and Wright 1949).

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Untitled

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American toads are the most widespread toad species in North America.

There are two subspecies of American toads, eastern and dwarf. Dwarf American toads live mainly in the west, eastern American toads live in the eastern portions of the range.

Contrary to folk-belief, you will not get warts if you touch a toad. However, the defensive chemicals in toad skin are toxic to humans, so its important to wash one's hands carefully after handling one.

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Behavior

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American toads have one of the most notable calls of all toads. They give off long trill sounds that each last between 4 and 20 seconds. American toads use this call as a way to attract females for breeding. Their calls become frantic, loud, and constant during mating season. Many young males continue to call late into the summer. When they call, their throats puff out like large, inflatable balloons.

American toads also use body postures, touch, and chemical cues for communicating.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: choruses

Perception Channels: visual ; tactile ; acoustic ; chemical

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Conservation Status

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American toads have no special conservation status, as they are still common in most of their range. Some populations have declined in recent years, possibly due to pollution.

US Migratory Bird Act: no special status

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

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Life Cycle

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Female American toads lay their eggs in freshwater. Hatching occurs 3 to 12 days after laying, depending on the temperature of the water. The tadpoles group together and feed and grow for 40 to 70 days.

When the tadpoles hatch they have gills located on the sides of their heads just posterior to their mouths. During the first 20 days the tadpoles start to form their hind legs. The legs grow slowly, but continuously. After 30 to 40 days the front legs, which were previously covered by a layer of skin, appear. At the same time that the front legs emerge, the tadpoles' gills disappear, and the tadpoles start to breathe "atmospheric" air. Between the last two or three days of development, they complete their metamorphosis, resorbing their tails and strengthening their legs. They also stop eating plants in favor of animal matter.

Newly-metamorphosed toads stay near their pond for a few days (or longer if the climate is dry), and then disperse and begin to live primarily on land. American toads continue to grow until they reach their full adult size of approximately 75 mm.

American toads, while still growing, shed their external skin every couple of weeks or so. Older frogs lose their skin around four times yearly. The skin peels off in one piece, and is collected under its tongue, where it is then gulped down.

Development - Life Cycle: metamorphosis

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Benefits

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There are no negative impacts of American toads on humans.

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Benefits

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American toads eat many species of pest insects and other invertebrates. They are widely considered friends to gardeners and farmers. The toxins produced by their skin may eventually prove useful in medical research.

Positive Impacts: research and education; controls pest population

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Associations

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American toads are responsible for controlling the populations of many kinds of insects. The number of insects they eat makes them a crucial part of controlling these populations.

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Grossman, S. 2002. "Anaxyrus americanus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Anaxyrus_americanus.html
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Trophic Strategy

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Adult American toads are carnivores, but toad tadpoles are considered herbivores, because they graze on aquatic vegetation (algae).

Adult American toads are generalists. They eat a wide variety of insects and other invertebrates, including snails, beetles, slugs, and earthworms. Unlike most toads, who wait for prey to come along and pounce on it, American toads can shoot out their sticky tongues to catch prey. They also may use their front legs in order to eat larger food. They grasp their food and push it into their mouths. One American toad can eat up to 1,000 insects every day.

Toads do not drink water but soak it in, absorbing moisture through their skin.

Animal Foods: insects; terrestrial non-insect arthropods; terrestrial worms

Plant Foods: algae

Primary Diet: carnivore (Eats non-insect arthropods); herbivore (Algivore)

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Distribution

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American toads, Anaxyrus americanus, are only native to the Nearctic region. They are found throughout large portions of North America, from northern Chihuahua in Mexico, northward to James Bay in Canada and eastward from the Imperial Valley of California and the Columbia River Valley in Washington and Oregon to the Atlantic coast from Florida to southern Quebec. They are generally not present in the most southern states or, if they are, only in the northern part. These toads have an immense ability to adapt to their surroundings as long as there is a source of semi-permanent water for them to use in the breeding season. This quality has allowed them to successfully colonize suburban and agricultural areas.

Biogeographic Regions: nearctic (Native )

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Habitat

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American toads require a semi-permanent freshwater pond or pool for their early development. They also require dense patches of vegetation, for cover and hunting grounds. Given these two things and a supply of insects for food, American toads can live almost everywhere, ranging from forests to backyards. They are common in gardens and agricultural fields. During daylight hours they seek cover beneath porches, under boardwalks, flat stones, boards, logs, wood piles, or other cover. When cold weather comes, these toads dig backwards into their summer homes or may choose another site in which to hibernate.

Habitat Regions: temperate ; terrestrial ; freshwater

Terrestrial Biomes: chaparral ; forest ; rainforest ; scrub forest ; mountains

Aquatic Biomes: lakes and ponds; rivers and streams

Wetlands: marsh ; swamp ; bog

Other Habitat Features: urban ; suburban ; agricultural ; riparian

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Life Expectancy

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In the wild most American toads probably don't survive more than a year or two. The majority die before transforming from tadpoles into toadlets. However, they are capable of living much longer. Some toads have lived longer than 10 years in the wild. There is a documented account of a captive toad that lived to the ripe old age of 36 and was killed by mistake.

Range lifespan
Status: wild:
0 to 10 years.

Average lifespan
Status: wild:
< 1 years.

Range lifespan
Status: captivity:
0 to 36 years.

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Morphology

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American toads have short legs, stout bodies, and thick skins with noticeable warts. These warts can be colored red and yellow. The warty skin contains many glands that produce a poisonous milky fluid, providing these toads with excellent protection from many of their predators. This poison is only harmful if it is swallowed or if it gets in the eyes, but it can make many animals very sick.

The skin color of American toads is normally a shade of brown, but it can also be red with light patches, olive, or gray. The bellies are a white or yellow color. Toad skin color changes depending on temperature, humidity, and stress. The color change ranges from yellow to brown to black. American toads have four toes on each front leg and five toes connected together by a webbing on each hind leg. The pupils of American toads are oval and black with a circle of gold around them. The sexes can be distinguished in two ways. Males have dark colored throats, of black or brown, while females have white throats and are lighter overall. Also, female American toads are larger than male American toads. American toads are between 50 and 100 mm in length but are usually around 75 mm. American toads can be distinguished from other species of toads by the presence of several dark spots on their backs which contain only one or two warts each. These black spots are sometimes circled with white or yellow. Some types of American toads have a prominent ridge on the top of their heads.

The eggs of American toads are black on top and white on the bottom (countershaded), and embedded in long strings of clear sticky gel. The larvae that hatch from eggs are called "tadpoles." They are dark (almost black) with smooth skin, round bodies, and a somewhat rounded tail. Like adult toads, larvae have defensive chemicals in their skin. They grow to over a centimeter in length before transforming. Newly-metamorphosed toadlets are usually 0.8 and 1.3 cm long when they first emerge. Their coloration is similar to that of adult toads.

Range length: 50 to 102 mm.

Average length: 75 mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous

Sexual Dimorphism: female larger; sexes colored or patterned differently

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Associations

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The main predators of American toads are snakes. One species, eastern hognose snakes, specializes on eating toads. Some snakes, such as garter snakes, are immune to the poisonous glands of American toads. When these toads are faced with a predator that is immune to their poison they will sometimes urinate on themselves to become a less attractive meal. They also inflate their bodies with air to make themselves more difficult for a snake to swallow.

Female toads prefer to lay their eggs in ponds without fish. The eggs they lay are countershaded: lighter on the bottom and darker on the top to blend in with the background when viewed from above or below.

Tadpoles avoid predators by swimming in very shallow water, and by swimming close together in schools during the day. They also have toxic chemicals in their skin that discourage some potential predators. Metamorphosed toads are cryptically colored, and are actively mainly at night, making it harder for predators to find them.

Known Predators:

  • diving beetles (Dytiscidae)
  • predaceous diving bugs (Belostomatidae)
  • garter snakes (Thamnophis)
  • hognose snakes (Heterodon)
  • hawks (Accipitridae)
  • herons (Ardeidae)
  • raccoons (Procyon lotor)

Anti-predator Adaptations: cryptic

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Reproduction

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Breeding occurs in the months of March or April, but may extend into July. It usually triggered by warming temperatures and longer days. The males always arrive on the mating grounds well ahead of females. They congregate in shallow wetlands, ponds, lakes and slow-moving streams. After finding a suitable area, the male toads establish territories and begin calling the females. Females may choose their mates by assessing the males' breeding calls as well as the quality of the defended breeding territory.

Male toads get dark horny pads on their first and second two toes on their forelegs. This helps them close their front limbs around a female's abdomen in a posture called "amplexus". Once a female comes close, any nearby male will attempt to mate with her. The male holds on to the female, and she moves to a suitable location in the water to lay eggs. When she releases her eggs, he releases sperm to fertilize them (like most frogs and toads, fertilization is external).

Mating System: polygynous ; polygynandrous (promiscuous)

After mating takes place, the females lay their eggs in the water, in long spiral tubes of jelly. They lay 4000 to 8000 eggs in two rows. When each row of eggs is stretched it generally measures between between six and twenty meters long (20 to 66 ft.). Each individual egg is 1.5 mm in diameter. The eggs mature fastest at higher temperatures. They generally hatch in 3 to 12 days. After developing for 40 to 70 days, the tadpoles transform into adults. This usually takes place from June to August, depending on location. They reach sexual maturity at around 2 to 3 years of age.

Breeding interval: American toads breed from once yearly.

Breeding season: American toads breed from March to July each year, depending on location.

Range number of offspring: 4000 to 8000.

Range time to hatching: 2 to 14 days.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Range age at sexual or reproductive maturity (male): 2 to 3 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

Female toads provide nutrients for their eggs inside their bodies. Once the eggs are laid and fertilized, the parents ignore them.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female)

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American toad

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The American toad (Anaxyrus americanus[2]) is a common species of toad found throughout the eastern United States and Canada. It is divided into three subspecies—the eastern American toad (A. a. americanus), the dwarf American toad (A. a. charlesmithi), and the rare Hudson Bay toad (A. a. copei). Recent taxonomic treatments place this species in the genus Anaxyrus instead of Bufo.[2][3][4]

Tadpoles

The eggs of the American toad are laid in two strings and can hatch in 2–14 days. When hatched the tadpoles are recognizable by their skinny tails in relation to the size of their black bodies. They may advance to adulthood in 50–65 days. When metamorphosis is completed, the "toadlets" may stay in the water for a short period of time before they become mostly land based. Often entire groups of tadpoles reach the toadlet stage at once and a mass migration to higher ground takes place usually to shaded areas of mid range and upland forests bordering the marshes from where they bred. Toadlets can be observed eating microscopic bugs as fast as they can in the ground area they roam between various vegetation; they are also known to eat ants, spiders, slugs and worms. Studies have shown that they have a mutualistic relationship with Chlorogonium algae, which makes tadpoles develop faster than normal.

Tadpoles have several mechanisms to reduce predation.[5] They avoid predators by swimming in very shallow water often with thick grass vegetation, and by swimming close together in schools during the day. Tadpoles also produce toxic chemicals in their skin that discourage some potential predators. Fish have been reported to die after consuming one tadpole; however, most fish quickly learn to avoid eating American toad tadpoles. The tadpoles are also very small and they are a solid black color.[6]

Biogeography

Based on DNA sequence comparisons, Anaxyrus americanus and other North American species of Anaxyrus are thought to be descended from an invasion of toads from South America prior to the formation of the Isthmus of Panama land bridge, presumably by means of rafting.[7]

Subspecies

Races tend to hybridize with Anaxyrus woodhousii in their overlapping ranges.

Eastern American toad

 src=
Eastern American Toad in Ohio
 src=
Eastern American Toad showing ground leaf camouflage in Darien Lakes State Park
 src=
Eastern American Toad showing bare ground camouflage in Darien Lakes State Park
 src=
Detail of parotoid glands

The eastern American toad (A. a. americanus) is a medium-sized toad usually ranging in size from 5–9 cm (2.0–3.5 in);[8] record 11.1 cm (4.4 in).[9] The color and pattern is somewhat variable, especially for the females. Skin color can change depending on habitat colors, humidity, stress, and temperature. Color changes range from yellow to brown to black, from solid colors to speckled. Their breeding habits are very similar to Anaxyrus fowleri. The call or voice of a breeding male is a high trill, lasting 6–30 seconds,[9] similar to a ringing telephone. They hibernate during the winter. The eastern American toad has spots that contain only one to two warts. It also has enlarged warts on the tibia or lower leg below the knee. While the belly is usually spotted, in some areas many are, and it is generally more so on the forward half (in some rare individuals there may be few or no spots). This subspecies of the American toad has no or very little markings on it. The spades on the back legs are blackish. Some toads of this subspecies have a more pervasive red and deep brown color, many with red warts on their bodies. Also eastern American toads have parotoid glands that are the same color as the surrounding skin. The glands don't usually have any patterning on them.

Other species that may be confused with the eastern American toad are Fowler's toad, which has three or more warts in the largest dark spots, and in the far west of its range woodhouse's toad. Fowler's toad can be especially difficult to identify in comparison to the eastern American toad but one difference is that it never has a spotted belly and both cranial crests touch the parotoid glands. Also, Fowler's toads are very fast hoppers (bursts of 5–10 fast hops) in comparison to Eastern toads lethargic, casual hopping and walking locomotion. In the eastern American toad these crests almost never touch the parotoid glands, which secrete bufotoxin, a poisonous substance meant to make the toad unpalatable to potential predators. Bufotoxin is a mild poison in comparison to that of other poisonous toads and frogs, but it can irritate human eyes and mucous membranes[10] and is dangerous to smaller animals (such as dogs) when ingested.[11]

American toads require a semi-permanent freshwater pond or pool with shallow water in which to breed, to gather their water supplies in times of drought or as a routine,[9] and for their early development. They also require dense patches of vegetation, for cover and hunting grounds. Given these two things and a supply of insects for food, American toads can live almost everywhere, ranging from forests to flat grassland. Females when caught are silent and easily tamed, adapting to terrarium life readily, while the smaller males are readily communicative. The smaller males do not adapt well to terrarium life and should be released after a few days of observation. Adult toads are mostly nocturnal, although juveniles are often abroad by day. When it rains, these toads will become active and can be observed eating robustly worms and insects leaving their burrows and walking in front of an opportunist toad. These toads are 'creatures of habit' once they have a certain area they prefer to live within... an acre of wooded forest with water in proximity for soaking, a home with cool ledges and window wells; they commonly seek cover in burrows, under boardwalks, flat stones, boards, logs, wood piles, or other cover. When cold weather comes, these toads dig backwards and bury themselves in the dirt of their summer homes, or they may choose another site in which to hibernate.[6] Their diet includes crickets, mealworms, earthworms, ants, spiders, slugs, centipedes, moths, and other small invertebrates. Some of these toads have been known to live over 30 years and currently a female specimen (over 13 centimeters long) is living healthily into her late 30s. Another female toad of 17 centimeters is known to have existed in Wisconsin from Washington Island on Lake Michigan.

The eastern American toad may be confused with the Canadian toad in the area where they overlap, but the cranial crests in the American toad do not join to form a raised "boss" (bump) like they do in the Canadian toad. Its range also overlaps with the southern toad's, but in this species the cranial crests form two unique knobs.

Dwarf American toad

The dwarf American toad (A. a. charlesmithi), is a smaller version of the American toad, which reaches lengths of about 6 cm (2+14 in), is generally a dark reddish color ranging to light red in some specimens in isolated populations. The spots on the back are reduced or absent, and when present they contain a few small red warts and a black ring around it like in the normal American toad. The warts are always darker than the skin of the toad. Some specimens have a white dorsal line in the middle of their backs. The ventral surface or belly is usually cream colored with a few dark spots in the breast area. This subspecies can be distinguished from the above-mentioned species in the same manner as for the eastern American toad. The southwestern portion of the Dwarf American toad's range overlaps with that of the Gulf Coast toad. The latter species is distinguished by the presence of a dark lateral stripe as well as a deep "valley" between its prominent cranial crests. It eats mainly spiders, worms and small insects.

Hudson Bay toad

The Hudson Bay toad (A. a. copei) is a rare Canadian subspecies of A. americanus.[12] This subspecies of the American toad has been seen in the northern parts of Ontario where there are a few isolated populations. These northern dwarf toads mostly have the red coloring on the sides of their bodies and have an unusually high number of warts for the subspecies. Interbreeding with eastern American toads caused this subspecies to lose the red coloring on their backs.

Inbreeding avoidance

Toads display breeding site fidelity, as do many other amphibians. Individuals that return to natal ponds to breed will likely encounter siblings as potential mates. Although incest is possible, Anaxyrus americanus siblings rarely mate.[13] These toads likely recognize and actively avoid close kins as mates. Advertisement vocalizations by males appear to serve as cues by which females recognize their kin.[13]

Gallery

References

  1. ^ IUCN SSC Amphibian Specialist Group (2015). "Anaxyrus americanus". IUCN Red List of Threatened Species. 2015: e.T54570A56843565. doi:10.2305/IUCN.UK.2015-4.RLTS.T54570A56843565.en. Retrieved 9 January 2020.
  2. ^ a b Frost, Darrel R. (2015). "Anaxyrus americanus (Holbrook, 1836)". Amphibian Species of the World: an Online Reference. Version 6.0. American Museum of Natural History. Retrieved 23 December 2015.
  3. ^ Review: The Amphibian Tree of Life, by Frost, D.R. et al., Amphibiatree
  4. ^ "Bufonidae". AmphibiaWeb: Information on amphibian biology and conservation. [web application]. Berkeley, California: AmphibiaWeb. 2015. Retrieved 23 December 2015.
  5. ^ "ADW: Bufo americanus: Information". Animaldiversity.ummz.umich.edu. Retrieved 2011-04-01.
  6. ^ a b "University of Notre Dame: Yellow perch predation on tadpoles" (PDF). Retrieved 2011-04-01.
  7. ^ Pauly, G. B.; Hillis, D. M.; Cannatella, D. C. (November 2004). "The History of a Nearctic Colonization: Molecular Phylogenetics and Biogeography of the Nearctic Toads (Bufo)". Evolution. 58 (11): 2517–2535. doi:10.1554/04-208. PMID 15612295. S2CID 198155461.
  8. ^ American toad (Bufo americanus) Archived June 18, 2009, at the Wayback Machine, Natural Resources Canada
  9. ^ a b c Conant, Roger (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Boston: Houghton Mifflin. ISBN 0-395-19979-4.
  10. ^ Lannoo, Michael. "Amphibian Declines: The Conservation Status of United States Species". Amphibiaweb. Regents of the University of California. Retrieved 8 May 2019.
  11. ^ Vigil, Stacey; Mengak, Michael (October 2006). "American Toad (Bufo americanus)". WSFS Natural History Series. 7: 2–3.
  12. ^ "American toad". Frog Toad Newt and Salamander Species of Canada. amphibians.ca. Retrieved 17 August 2013.
  13. ^ a b Waldman, B; Rice, JE; Honeycutt, RL (1992). "Kin recognition and incest avoidance in toads". Am. Zool. 32: 18–30. doi:10.1093/icb/32.1.18.

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American toad: Brief Summary

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The American toad (Anaxyrus americanus) is a common species of toad found throughout the eastern United States and Canada. It is divided into three subspecies—the eastern American toad (A. a. americanus), the dwarf American toad (A. a. charlesmithi), and the rare Hudson Bay toad (A. a. copei). Recent taxonomic treatments place this species in the genus Anaxyrus instead of Bufo.

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