AMPHIBIAWEB
Incilius nebulifer
Gulf Coast Toad, Coastal Plain Toad
family: Bufonidae

© 2009 John P. Clare (1 of 14)

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Country distribution from AmphibiaWeb's database: Mexico, United States

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Conservation Status (definitions)
IUCN (Red List) Status Least Concern (LC)
See IUCN account.
NatureServe Status Use NatureServe Explorer to see status.
CITES
Other International Status None
National Status None
Regional Status None

   

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bookcover The following account is modified from Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo (©2005 by the Regents of the University of California), used with permission of University of California Press. The book is available from UC Press.

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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