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EASTERN
AMERICAN TOAD
Bufo a. americanus
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| INTRODUCTION |
The American toad is among
the most well recognized amphibians of southern New England. It
is found throughout Rhode Island, ranging from relatively pristine
forest patches in western Rhode Island to somewhat degraded urban
areas in the Providence area. American toads often frequent shaded
yards and parks after a spring rain, as they generally prefer areas
where conditions are moist and food sources abundant. Toad populations
appear to be relatively secure in the region, with the major cause
of mortality seemingly attributed to road activity during peak migrations.
The far less common Fowler's toad (Bufo fowleri) is similar
in appearance and can easily be mistaken for an American toad- especially
as juveniles and young adults.
To add to the confusion, these two species are thought to hybridize
in areas where habitat is suitable to both species. American toads
are a facultative vernal
pool species.
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| IDENTIFICATION |
- The American toad is a rotund, terrestrial frog with
a large-wide head, short limbs, and rough, warty skin.
- Mature females are significantly larger than males and
feel noticeably rougher in texture when handled.
- Commonly, the spotted dorsum
is dominantly brown in color, but there is much variation.
Individuals vary from brick-red to olive to greenish gray
to nearly black; furthermore, coloration may change depending
upon the season, environment, time of day, age, and sex.
- The chest and forward part of the abdomen is cream-colored
and speckled with small black flecks or spots. Fowler's
is immaculate- white with no dark flecking.
- Males have dark throats (Dickerson
1906).
- The colors of the usually roundish spots on the dorsum
also vary. Shades of red, brown, and black have been noted.
Female's dorsal warts may be noticeably pointed (Hunter
et al. 1999).
- In the American toad, each of the larger spots contains
1-2 round warts (small glands). Fowler's Toads tend to
have 3-4 warts per spot. The legs, feet, and thighs are
also warty.
- The two cranial ridges
on top of the head have lateral branches extending
behind the eye. Behind these ridges are the large, bean-shaped
parotid glands. The
parotid glands are either separated from the cranial ridge
behind the eye, or connected with it by a short spur (Hunter
et al. 1999). On Fowler's toad, the cranial ridges and
parotid glands touch completely.
- A light, narrow mid-dorsal stripe may be present. Fowler's
Toad has a light mid-dorsal stripe.
- Breeding males have enlarged, darkened nuptial pads
on the dorsal (upper) surface of the thumbs that are used
to grasp the female during amplexus. During the breeding
season, the nuptial pads are the most useful characteristic
to distinguish genders.
- During the breeding seasons females tend to be more
reddish overall.
- Voice: A long trilling whistle, lasting 6-30
seconds, with some individual variation in pitch and tone
(Gage 1904; Wright
and Wright 1949; Conant
and Collins 1991).
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(1) American Toad color variation.
(2) Notice the cranial ridge
and parotid gland behind the eye
(3) top photo: mid-dorsal stripe
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| SIZE |
| AGE / SEX
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SVL (SNOUT
VENT LENGTH) (cm) |
SAMPLE SIZE
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AVERAGE
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RANGE |
Std. Deviation
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ADULT FEMALE
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7.1
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6.0- 8.7 |
0.7
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68
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ADULT MALE
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6.1
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5.1- 7.2 |
0.5
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146
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JUVENILE
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3.3
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0.8 |
1.3- 5.7
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309
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METAMORPH
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1.6
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0.7- 2.3 |
0.3
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360
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| AGE/ SEX
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MASS (g)
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SAMPLE SIZE
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AVERAGE
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RANGE |
Std. Deviation
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ADULT FEMALE
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43.5
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16.4- 75.3 |
15.1
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68
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ADULT MALE
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26.3
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13.7- 38.4 |
5.0
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146
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JUVENILE
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4.5
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0.5- 15.7 |
3.5
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309
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METAMORPH
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0.4
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0.1- 1.0 |
0.2
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360
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| RELATIVE ABUNDANCE |
Rhode Island
Common, much
more likely to be detected during the breeding season in permanent
ponds or ponds that often do not dry every year.
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Regional
Despite
some localized extirpations and high road mortality, American toads
are presently thought to be abundant and widespread in southern
New England (Klemens 1993).
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| DISTRIBUTION |
Rhode Island
American Toads are widespread
throughout mainland Rhode Island, but are absent from some of the state's
many islands. We found evidence of American toads breeding (egg masses
and larva) in 10 of 119 randomly-selected ponds in Rhode Island during
research in 2000 (Paton and Egan 2001).
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Regional
Widespread and
common (Klemens 1993; DeGraaf and
Yamasaki 2001).
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General
Found throughout eastern
North America from Hudson's Bay in northern Canada to the southern United
States, except for Florida's Gulf Coast, coastal areas in the southeast,
parts of New Jersey, Long Island, New York (Klemens 1993).
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| HABITAT NON BREEDING |
In general,
American toads spend only a few weeks at breeding sites, then disperse
into the upland and are solitary and seldom seen. American toads
are believed to be habitat generalists because they are found in
all forest types in New England and most non-forested habitats with
the exception of high-elevation habitats (alpine and Krummholz)
(DeGraaf and Yamasaki 2001). When encountered, they are found in
a variety of habitats including: forests- deciduous and evergreen,
shrublands, open fields, residential yards, urban parks, and fringes
of water bodies (Hunter et al 1999). Toads may be seen throughout
the fall, especially after a rainy night, until the weather turns
cold. When winter sets in, toads burrow deep into soft soils or
forest floor litter and hibernate until the following spring. Unfortunately,
little is known in our area about the wintering habitats and requirements
of American Toads (Raithel unpubl. ms).
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| HABITAT BREEDING |
American toads breed
primarily in permanent fresh water, but alternative breeding sites
include: temporary pools, ditches, old beaver flowages, flooded
gravel pits, artificial ponds, coves in large lakes, floodplains
of rivers, and shallow portions of streams. The common requirement
among these habitats seems to be areas of shallow water (Klemens
1993; Hunter et al.1999). In Rhode Island, we found that American
toads were most likely to breed in permanent ponds, although they
occasionally were detected in ponds that dried by the end of July
(Paton and Egan 2001).
Ponds used by breeding American toads can be found in a number of
habitats located from sea level to mountain elevations-ranging from
suburban backyards in gardens and woods to mountain wilderness;
nearly any place where toads can find hiding places, some moisture,
and an abundance of insects and other invertebrates for food (Conant
and Collins 1991).
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| HYDROLOGY |
Found in ponds with a variety
of hydroperiods, although they tend to breed more frequently in
permanent ponds (Paton and Egan 2001).
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| MOVEMENT CHRONOLOGY |
Adult immigration
American toads typically immigrate to breeding ponds in southern
Rhode Island during the last week of April (Paton
and Crouch In press).
Metamorphs emigration
We found peak emigration of American toad metamorphs to be at
the end of July, approximately 3 months after peak immigration
of adults (Paton and Crouch In press). However, Klemens (1993)
reported metamorphosing young as early as 10 June in Connecticut.
Movement phenology of American Toad. Data gather over a three
year period in 10 ponds surrounded by drift net fences.
(Paton et al. 2000; Paton and Crouch In press).
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| REPRODUCTION |
| The breeding season for American
toads is temperature dependent, peaking typically during mid-April
in Rhode Island (Paton and Crouch In press). When environmental
conditions are optimal, males toads move to breeding sites.
Arriving prior to the females, males begin their harmonious
trilling. Females, lured by the call of males, arrive a few
days later. Breeding typically occurs within two weeks of
emergence and is usually brief, commonly less than 15 days,
but calling can continue sporadically until early July (Knox
1999), although Klemens (1993) reported breeding choruses
in Connecticut only from mid-March through early June. |
American toads in amplexus
(male is on top of female)
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| EGG MASS |
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Gelatinous eggs are laid in two long thin parallel strings
usually spiraling on the open bottom or entangled in submerged
vegetation. The development of the thousands of eggs- numbering
from 4,000 to 12,000 eggs (Degraaf and Rudis 1983)- is partially
temperature dependent, but hatching usually occurs within
3 to 12 day (Knox 1999).
American toad egg strings can be separated from Fowler's
toads by the presence of an inner layer in the gelatin tube
and partitions separating the eggs, which are usually in
single file (Wright and Wright 1949).
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Strand of American toad eggs |
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| LARVAE |
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The unicolored black tail musculature and body, the transparent
ventral and dorsal fins, and the rounded tipped tail makes
the toad tadpole readily distinguishable all other Rhode
Island amphibians except Fowler's Toad. Eyes
are dorsal. All other species of tadpoles in Rhode
Island, except Fowler's toad, have lateral or dorsal-lateral
eyes.
After hatching, the tadpoles tend to school in the shallow,
sunny waters feeding on suspended matter, algae, plants,
and carrion. Basking in these warmer waters raises body
temperature and thereby increases metabolic rate and accelerates
development (Klemens 1993). Tadpole metamorphosis is complete
in 5 to 10 weeks.
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American toad tadpole |
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| METAMORPHS |
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Dorsal view
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Ventral view
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| JUVENILES |
| Age to maturity: According
to Dickerson (1906) American toads reach sexual maturity in 3 to
4 years; however, Hamilton (1934)
found toads mature a bit sooner - in 2 to 3 years. |
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| FOOD |
Adults
Adult American toads feed
from dawn through evening hours; however, foraging activities decline
during periods of high temperatures. They feed primarily on invertebrates
with the type of prey generally determined by availability and abundance
-though studies have shown that toads can be selective (Hunter et
al 1999). Common food types include: adult and larval terrestrial
and aquatic insects, arthropods, slugs, and earthworms, sowbugs,
spiders, centipedes, and millipedes (Klemens 1993; Degraaf and Rudis
1983). The benefits of American toads have been known since at least
1915. Mattoon (2001) quoted from
a study by Kirkland, in a US Department of Agriculture report, who
documented the stomach contents of 149 toads, and found pest species
including gypsy moths, tent caterpillars, and beetles account for
62% of the toads diet. He estimated one adult toad may consume 10,000
pest insects in a 90-day period.
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Larvae
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| PREDATION |
Adults
Predominate toad predators
include nocturnal mammals, particularly raccoons and skunks, and
a variety of snakes including: garter (Thamnophis s. sirtalis),
hognose (Heteroden platyrhinos), and water snakes (Nerodia
s. sipedon). Toads employ anti-predator defenses including camouflage,
escape by burrowing, ejection of urine, and noxious or toxic skin
secretions released from enlarged parotid glands and warty skin
(Knox 1999). The secretions are mainly cardiotoxic steroids which
some mammalian predators (including domestic dogs and cats) painfully
learn to avoid (Knox 1999).
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Larvae
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| CONSERVATION CONCERNS |
Presently thought
to be relatively secure in the region (Klemens 1993; DeGraaf and Yamasaki
2001).
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NEXT SPECIES
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