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Bufo nebulifer Girard, 1854
Coastal-Plain Toad
Joseph R. Mendelson III1
I follow Mulcahy and
Mendelson (2000) in recognizing Coastal-Plain toads (Bufo nebulifer) as
a species distinct from Gulf Coast toads (Bufo valliceps). This
study was based on an analysis of mtDNA sequences and corroborated comments by Mendelson
(1998) that showed the northern and southern populations of the widespread taxon
Bufo valliceps were likely not conspecific. The taxon
Bufo nebulifer was proposed by Girard (1854) as a replacement name for
the preoccupied taxon Bufo granulosus Baird and Girard, 1852a, type
locality: “between Indianola and San Antonio, Texas.” Mulcahy and
Mendelson (2000) resurrected the taxon B. nebulifer from the
synonymy of B. valliceps Wiegmann, 1833, and applied it to populations
generally north of the coastal village of Palma Sola, Veracruz, Mexico. Further
discussions of variation in B. valliceps with respect to B.
nebulifer appear in Mendelson (1998) and McCranie and Köhler (2000).
Note that the vast majority of literature regarding B.
valliceps—especially that relevant to natural history and
behavior—actually considers northerly populations now referred to as Coastal-Plain
toads (B. nebulifer).
1. Historical versus Current Distribution. Coastal-Plain toads (Bufo
nebulifer) are found in a wide variety of habitats along the Gulf Coastal Plain
from central Veracruz, Mexico, northward to north-central Texas and extending eastward
into southern Louisiana and extreme southwestern Mississippi. The species ranges
westward in Texas, occurring in the Hill Country of the Edwards Plateau region and along
the Rio Grande, Devil’s, and Pecos River systems. A record from further up
the Rio Grande system, near El Paso, Texas, represents an accidental introduction
(Dixon, 2000). Apparently disjunct populations in southern Arkansas and northern
Louisiana may also represent dispersal along river systems (Dundee and Rossman,
1989). The range map published by Porter (1970) is misleading because it shows the
combined ranges of Bufo valliceps and B. nebulifer,
includes localities for numerous misidentified specimens (see Mendelson, 1997a,b; Frost,
2000c; Mendelson, 2001) and lacks many records reported since 1970 (e.g., additional
records from Texas reported by Dixon, 2000). The map presented by Mulcahy and
Mendelson (2000, fig. 5) and represented here for U.S. populations more accurately
illustrates the distribution of both B. nebulifer and B.
valliceps.
2. Historical versus Current Abundance. Reports concerning the abundance of
Coastal-Plain toads typically state that they are common or abundant wherever they occur
(e.g., Penn, 1943; Raun, 1959). Size of local populations appears to vary with
respect to annual rainfall patterns; in some cases appearing to increase or decrease by
50% between years. Despite this variation, the sex ratio of the population remained
male biased by about 2:1 over a 5-yr study (Blair, 1960a). Recent reports from the
United States (e.g., Foley, 1994; Dixon, 2000) indicate that they remain common or
abundant in all areas of their distribution. Less information is available from
the area of the range occurring in Mexico, but Martin (1958) reported this species to be
widespread and common in every variety of habitat ≤ 1,550 m in the Gómez
Farías region of the Sierra Madre Oriental, in southern Tamaulipas, Mexico.
Large series of museum specimens from other localities in northeastern Mexico suggest
these toads have historically been abundant in these areas and continue to be so
today. They were observed to be common in several localities in northern Veracruz
between 1996–2000 (personal observations). With regard to Mexico, virtually
all published reports and most series of museum specimens correspond to populations
referable to B. valliceps in the southern areas of the country.
3. Life History Features.
A. Breeding.
Reproduction is aquatic. Coastal-Plain toads breed in many varieties of still
water, and their reproductive biology is generally similar to that of other
north-temperate species of Bufo.
i. Breeding migrations. Spring or summer rains in excess of about 3 cm usually
stimulate formation of choruses of calling males (Blair, 1960a). Individuals
congregate at suitable breeding sites throughout the summer rainy season; reproductive
behavior has been observed from March–August (Martin, 1958; Thornton, 1960; Wiest,
1982; Foley, 1994); Thornton (1960) observed a few calling males, but no females, as
early as February. Calling males and breeding activity were observed at
temperatures from 15–30 ˚C (Wiest, 1982). Sullivan and Wagner (1988)
reported variation in the frequency and duration of advertisement calls with respect to
size of the individual; call rate and effort also varied with respect to density of
calling males and their proximity to one another. Females do not remain at the
breeding site after eggs are deposited (Thornton, 1960). Larvae have been observed
in ponds from April–August (Wiest, 1982). Orientation to breeding sites by
Coastal-Plain toads apparently is at least partially based on olfactory cues (Grubb,
1973a).
ii. Breeding habitat. Coastal-Plain toads breed in a wide variety of still-water
habitats, including ponds, ephemeral wetlands, roadside ditches, and artificial
impoundments (Wright and Wright, 1949; Wiest, 1982; Foley, 1994; personal
observations). Toads may breed occasionally along the margins of rivers (e.g.,
Awbrey, 1963). Dundee and Rossman (1989) detail and provisionally accept the
arguments that Coastal-Plain toads breed in brackish waters. Adults began breeding
in a series of artificial pools within 1 yr of their installation at a field site in
Texas (Hubbs and Martin, 1967).
B. Eggs.
i. Egg deposition sites. Eggs are typically deposited in still, shallow water,
with or without emergent vegetation.
ii. Clutch size. The eggs of Coastal-Plain toads are usually deposited in double
rows that are strung out and pelagic; egg density in the rows ranges from 7–10 to
25–27 eggs/3-cm section of an egg string (Wright and Wright, 1949; Dundee and
Rossman, 1989). A single clutch may contain approximately 20,000 eggs (Blair,
1960a). A few females have been observed to produce two clutches of eggs during a
single, extended reproductive season (Blair, 1960a).
C.
Larvae/Metamorphosis.
i. Length of larval stage. At a laboratory-controlled temperature of 25 ˚C,
> 50% of a group of tadpoles hatched 24 hr after egg deposition and began
metamorphosis 19 d after egg deposition (Limbaugh and Volpe, 1957). In the wild,
eggs hatch 1–2 d after deposition and, after a 20–30 d larval period,
tadpoles metamorphose at 7.5–12 mm (Wright and Wright, 1949).
ii. Larval requirements. Eggs of Coastal-Plain toads exposed to temperatures <
18 ˚C or > 30 ˚C did not hatch (Hubbs et al., 1963). Eggs exposed to
temperatures > 30 ˚C also produced tadpoles that developed a variety of
deformities (Volpe, 1957; Hubbs et al., 1963). Similar experiments by Ballinger
and McKinney (1966) found the low lethal temperature also to be 18 ˚C, but the high
lethal temperature to be 38 ˚C. Short-term exposure (3 d) to acidic (pH 4)
conditions reduced body weights of tadpoles, but by 7 d after return to neutral (pH
7.2–7.6) conditions, tadpoles were at normal weight and metamorphosed normally
(Pierce and Montgomery, 1989). Exposure to acidic conditions did not result in
mortality of tadpoles (Rosenberg and Pierce, 1995).
a. Food. Tadpoles are presumed to be generally algivorous, scraping plant and
animal material off submerged substrates.
b. Cover. Cover objects are not specifically sought by tadpoles. Tadpoles
usually occur in groups and are conspicuous in the water.
iii. Larval polymorphisms. Not known to occur.
iv. Features of metamorphosis. In a laboratory study with temperatures held at 25
˚C, most Coastal-Plain toad tadpoles hatched 24 hr after egg deposition (Limbaugh
and Volpe, 1957). Hindlimb buds appeared after 5 d, forelimbs protruded around 21
d; metamorphosis began around 19 d and was complete by around 28 d.
v. Post-metamorphic migrations. Newly metamorphosed Coastal-Plain toads exhibit a
short period of residency at their natal pond, then migrate away in a direction
perpendicular to the shoreline (Grubb, 1973b). However, under dry conditions,
recently metamorphosed animals may remain by the pond margin for extended periods
of time until favorably wet conditions allow dispersal; mortality is high during this
time (Blair, 1953).
D. Juvenile
Habitat. Similar to adults. Juvenile Coastal-Plain toads may remain
concentrated along margins of their natal pond for some time before dispersing (Blair,
1953; personal observations).
E. Adult
Habitat. Adult Coastal-Plain toads are associated with almost every variety of
habitat, including suburban and urban areas, and are frequently found in agricultural and
wet hardwood areas, although they are relatively uncommon in pinelands (Dundee and
Rossman, 1989; personal observations). They are commonly seen in suburban and some
urban areas, foraging for prey on lawns and under streetlights (personal
observations). Coastal-Plain toads are frequently found in railroad ditches or
roadside pools, garbage dumps, and storm sewers (McAllister et al., 1989; personal
observations). In urban environments, they are found frequently under concrete
slabs and gathered in groups in cracks and holes under sidewalks (Awbrey, 1963; Moore,
1976). During the day, Coastal-Plain toads seek cover and can be found under logs,
other cover objects (personal observations), or in rodent burrows (Wilks, 1963).
Neill and Grubb (1971) found Coastal-Plain toads from 2–5 m above the ground in oak
trees; they can be considered arboreal in that individual toads will find tree holes and
may use them repeatedly for periods of weeks. In Texas, individuals have been found
at the mouth of caves and, in one case, well down in a cave system (see Reddell,
1970). This species does not appear to be adversely affected by alteration of
native vegetation or by invasion of non-native vegetation. Adults may be found in
vegetated areas of coastal barrier islands within 30 m of saltwater (personal
observations). Timber harvesting practices at a site in southeast Texas did not
affect overall abundance of toads (Foley, 1994). Body temperatures of active toads
ranged from 22.3–27 ˚C (Brattstrom, 1963).
F. Home Range
Size. A male Coastal-Plain toad moved approximately 800 m in about 1 wk (Thornton,
1960). Another individual marked by Thornton moved approximately 1,200 m in 2 d
and was located approximately 1,600 m from its original point of capture 1 yr
later. Thornton also reported many toads regularly moving between two ponds about
100 m apart. Although toads clearly do wander relatively great distances, a
mark-recapture study (Awbrey, 1963) found that the majority of his marked toads (n = 49)
remained within a “home range” area within approximately 46 m from their
original site of capture. Homing experiments (Awbrey, 1963) indicated that
individual toads could relocate their site of capture after being removed distances up to
approximately 220 m.
G.
Territories. Individuals do not appear to defend territories. At breeding
aggregations, male combat and satellite behavior have not been observed (Wagner and
Sullivan, 1992). Toads appear to exhibit homing behavior towards breeding sites,
based on visual and olfactory cues (Grubb, 1970).
H.
Aestivation/Avoiding Dessication. Toads in breeding season have been known to take
refuge in rodent burrows during the day (Grubb, 1970) and under debris piles, logs, and
stones during drier parts of the summer (personal observations).
I. Seasonal
Migrations. Distinct migrations among habitats do not occur, but aggregations of
adults appear suddenly at temporary and permanent bodies of water during the prolonged
summer breeding season.
J. Torpor
(Hibernation). Coastal-Plain toads are typically inactive during winter and/or dry
seasons. Presumably they take refuge in burrows of other animals or under larger
debris piles.
K. Interspecific
Associations/Exclusions. Coastal-Plain and Fowler's toads (B.
fowleri) are broadly sympatric in Texas and Louisiana and natural hybrids are
relatively frequent (Blair, 1956b; Gosner and Black, 1958a; Dundee and Rossman,
1989). At ponds shared by both species in Texas, 7–9% of amplectant pairs
were interspecific (Thornton, 1955, 1960; L.E. Brown, 1971a). Volpe (1960) reported
B. nebulifer-woodhousei (Woodhouse's toad) hybrids to be
viable and vigorous, but sterile. Hybridization between B.
nebulifer and B. houstonensis (Houston toads) has been
implicated as one of several factors resulting in the Endangered status in the latter
species (L.E. Brown, 1971b; Brown and Mesrobian, 2002). Axtell (1958) described a
pond harboring a mixed chorus of Coastal-Plain toads, Texas toads (B.
speciosus), plains spadefoot toads (Spea bombifrons), Couch's
spadefoot toads (Scaphiopus couchii), and spotted chorus frogs
(Pseudacris clarki). Moore (1976) described mixed choruses of
Texas toads and Coastal-Plain toads, in which the former species was more abundant.
In these choruses, Coastal-Plain toads called from the margins of ponds rather than the
knolls and ledges around the pond seemingly favored by Texas toads. Kelly Irwin
(personal communication), working in Starr County, Texas, observed a mixed chorus of
Coastal-Plain toads, Texas toads, Couch's spadefoot toads, western narrow-mouthed toads
(Gastrophryne olivacea), sheep frogs (Hypopachus
variolosus), and Rio Grande leopard frogs (Rana
berlandieri). Coastal-Plain toads use pocket gopher burrows as refuges
(Wilks, 1963). Where Coastal-Plain toads are sympatric with marine toads
(Bufo marinus; extreme southern Texas and northeastern Mexico), adults
of these two species frequently are found together in a variety of habitats. I have
not observed these two species to form mixed breeding choruses or to share breeding
sites.
L. Age/Size at
Reproductive Maturity. Males 53–98 mm; females 54–125 mm (Wright and
Wright, 1949; Blair, 1956b, 1963b; Dundee and Rossman, 1989). Sexual maturity
appears to occur during the second year (Blair, 1953). Blair (1953) notes that 25
of 357 marked juvenile toads were recovered the following summer when they were
apparently sexually mature. Allowing for differences between sexes, Blair (1953)
suggests about 11% of juveniles reach sexual maturity. Growth rates are fastest
during the first year; one male grew 39 mm between mid August and late September.
M. Longevity.
Individuals in the wild are known to live 8 yr (Blair, 1960a).
N. Feeding
Behavior. Campbell and Davis (1968) examined the stomachs of 21 Coastal-Plain toads
and found the bulk of their diet to be composed of invertebrates such as isopods and
coleopterans, but also included were an eastern fence lizard (Sceloporus
undulatus) and a juvenile Fowler's toad. McGehee et al. (2001) also
reported a preponderance of isopods, along with numerous scorpions and relatively few
coleopterans. Most likely, Coastal-Plain toads are opportunistic predators taking a
wide variety of small animals based on their availability.
O. Predators.
Western ribbon snakes (Thamnophis proximus) and water snakes
(Nerodia rhombifera) will feed on Coastal-Plain toads (Wright and
Wright, 1949). Martin (1958) reported predation by cat-eyed snakes
(Leptodeira septentrionalis). In captivity, tiger salamanders
(Ambystoma tigrinum) will eat juveniles (Strecker, 1927).
Predation on tadpoles by diving beetles (Acilius semisulcatus) has been
reported (Neill, 1968). Brown (L.E., 1974) described an unsuccessful predation
attempt by an American bullfrog (Rana catesbeiana). Kelly Irwin
(personal communication) observed predation by an indigo snake (Drymarchon
corais) in Cameron County, Texas.
P. Anti-Predator
Mechanisms. Coastal-Plain toad eggs are toxic and/or distasteful to a wide variety
of potential predators (Licht, 1968). Their parotoid gland secretions are presumably
distasteful to some predators. Brown (L.E., 1974) described an unsuccessful
predation attempt by an American bullfrog in which the parotoid secretions by the toad
apparently caused the bullfrog to release it, unharmed, after an approximately 5-min
attempt to swallow it.
Q. Diseases.
No instances of diseases are known from wild populations.
R. Parasites.
Walton (1946) reported Nyctotherus cordiformis (Protozoa: Ciliophora)
from Coastal-Plain toads. Hoffpauir and Morrison (1966) reported Rhabdias
ranae (Nematoda) from the lungs of a specimen from eastern Texas.
McAllister et al. (1989) describe the following endoparasites from Coastal-Plain toads:
Opalina sp. (Protozoa: Sarcomastigophra); Adelina sp. and
Eimera sp. (Apicomplexa: Eucoccidiorida); Myxidium serotinum
(Myxozoa: Bivalvulida); Mesocestoides sp. (Cestoidea: Cyclophyllidea); and
Cosmocercoides variabilis (Nematoda: Ascaidida).
4. Conservation. Coastal-Plain toads are widespread and common throughout their
range. They are adaptable and seem to tolerate habitat alterations caused by
humans. In Mexico, they are more common in secondary habitats rather than primary
forest habitats, suggesting that this species may expand its range or increase in local
density following disturbance. Coastal-Plain toads are found in a wide variety of
habitats, including suburban and urban areas, and are commonly seen in suburban areas
foraging for prey on lawns and under streetlights. They are also found in railroad
ditches or roadside pools, garbage dumps, and storm sewers (McAllister et al., 1989;
personal observations). All of these observations suggest that Coastal-Plain toads
are in no need of special protection.
Acknowledgments. I was ably assisted in compiling literature relevant to
this account by J. Minnick, and the original manuscript was greatly improved by the
critical comments of the students in the U.S.U. Herpetology Group. I offer my
thanks to all these persons.
1Joseph R. Mendelson III
Department of Biology
Utah State University
Logan, Utah 84322-5305
sapo@biology.usu.edu
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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