Bufo debilis Girard, 1854
Charles W. Painter1
1. Historical versus Current Distribution. Green toads (Bufo debilis) were originally described by Girard (1854) with the type locality presented as "found in the lower part of the Rio Bravo (Rio Grande del Norte), and in the Province of Tamaulipas." Kellogg (1932) later changed this designation to Matamoros, Tamaulipas. Flores-Villela (1993) pointed out that both Schmidt (1953) and Frost (1985) erroneously stated that the type locality was restricted to Brownsville, Texas, by Sanders and Smith (1951), although there is no such restriction in that publication. Green toads consist of two recognized subspecies, eastern green toads (B. d. debilis) and western green toads (B. d. insidor; Crother et al., 2000), and range from southeastern Colorado and adjacent southwestern Kansas to Tamaulipas, San Luis Potosì, and Zacatecas (Mexico), and from southeastern Arizona to eastern Texas (Frost, 1985; Conant and Collins, 1991). Western green toads (B. d. insidior) were described as green toads by Girard (1854). Knowledge of the current distribution has not been greatly expanded since early descriptions (Sanders and Smith, 1951). The current distribution is expected to be similar to the historical distribution detailed as follows: Oklahoma (Bragg, 1950a,b; Black and Sievert, 1989); Texas (Lowe, 1964; Morafka, 1977; Dixon, 1987, 2000; Garrett and Barker, 1987); Kansas (Rundquist, 1979; Collins, 1982; Taggart, 1997a); Colorado (Hammerson, 1982a, 1999); New Mexico (Degenhardt et al., 1996); Arizona (Rosen et al., 1996); and Mexico (Flores-Villela, 1993).
2. Historical versus Current Abundance. Historical abundance is unknown, however localized populations have likely declined due to the conversion and disappearance of wetlands and low-lying areas used in reproduction. Green toads are localized but common in remaining areas of suitable habitat.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Stimulated by summer rains, males move from drier, terrestrial habitat to aquatic breeding sites, followed by females who are attracted by chorusing males.
Breeding occurs from late March to mid June (Wright and Wright, 1949) and into late July (Sullivan, 1984; Degenhardt et al., 1996). Taylor (1929) reported chorusing on 8 August in extreme southwestern Kansas, and Bogert (1962) reported males calling during the first 2 wk of August in southwestern New Mexico. Taggart (1997a) observed breeding behavior from 12 June–2 September in Kansas. Breeding aggregations are usually of short duration, lasting only 1–3 d in southeastern Arizona (Sullivan, 1984).
ii. Breeding habitat. Breeding occurs during or after summer rains. Green toads breed in temporary water sources including stock tanks, temporary rain pools, roadside ditches, or shallow pools in streams of intermittent flow.
i. Egg deposition sites. The eggs of green toads are poorly known and are not produced in the long strings typical of most Bufo (Zweifel, 1968b). Sites for egg attachment may be limited in the ephemeral pools generally used as breeding sites by green toads. Strecker (1926) indicated the eggs are laid in small strings that are attached to grass and weed stems.
ii. Clutch size. Taggart (1997a) reported a single clutch of 1,287 non-adhesive eggs laid by a female while in amplexus. The eggs were laid singly and no egg-strings were observed in the clutch. Twenty-five ova averaged 0.98 mm and another sample of 32 (measured before preservation) averaged 1.15 mm. Working in southeast Arizona, Zweifel (1968b) reported embryos hatched within 24 hr at 33.1 ˚C water temperature, while at 18.2 ˚C, hatching required 140 hr. Length at hatching (generally at Gosner stage 18–20) is about 3.1–3.4 mm.
C. Larvae/Metamorphosis. The labial tooth row formula of 2/2 is unique and diagnostic of the B. debilis group (B. debilis, the Mexican B. kelloggi, and Sonoran green toads [B. retiformis]) in North America (Zweifel, 1968b, 1970).
i. Length of larval stage. Uncertain and is dependent upon numerous environmental factors. Strecker (1926; Texas) suggested metamorphosis took fewer than 3 wk. Burkhart (1984) estimated larval life exceeded 25 d in Kansas, while Taggart (1997a) observed development from zygote to juvenile in 8 d.
ii. Larval Requirements.
a. Food. Tadpoles of green toads are a morphological type IV tadpole (Orton, 1953). They are a generalized pond-type tadpole that likely feeds on a variety of algae, detritus, and periphyton on or near the bottom of ephemeral pools.
b. Cover. Cover is generally unavailable in the ephemeral pools that support green toad tadpoles, although increased water turbidity, wind-blown debris, or vegetation, especially clumps of grass that has been inundated from flood-waters, may provide cover.
iii. Larval polymorphisms. Carnivorous or cannibal morphs are unknown in green toads.
iv. Features of metamorphosis. Metamorphosis is complete at about 19–20 mm SVL (Savage, 1954). Newly transformed toadlets have been found in southwestern New Mexico as late as 27 September (Seymour, 1972), although in New Mexico most metamorphosis takes place during late July to early August (Degenhardt et al., 1996).
v. Post-metamorphic migrations. Newly metamorphosed toadlets remain near the parent pool and disperse only when the pool evaporates or when they reach an age of about 2–3 mo (Bragg, 1950c). Creusere and Whitford (1976) reported juvenile green toads that remained at the hatching site for 55 d, using vegetative cover and fissures in the soil for shelter and for protection from desiccation.
D. Juvenile Habitat. Believed to be the same as adult habitat characteristics. Seymour (1972) reported green toad juveniles are active by day at 15 ˚C, often basking on mud banks in direct sunlight and increasing body temperature to 30 ˚C. Recently transformed toadlets often hide in the fissures formed in the mud of drying pools (Seymour, 1972; Creusere and Whitford, 1976; Taggart, 1997a).
E. Adult Habitat. Generally arid regions below 1,524 m (5,000 ft). Specific habitat characteristics include grasslands in Arizona (Lowe, 1964); plains grasslands in Colorado (Hammerson, 1982a); open grass plains and native prairie vegetation with considerable topographic relief in Kansas (Collins, 1982; Taggart, 1997a); lower desert grasslands; areas grown to mesquite and creosotebush; playa bottom grasslands to open bajada creosote community in New Mexico (Creusere and Whitford, 1976; Degenhardt et al., 1996); mesquite-shortgrass prairies, especially along valleys of small creeks; short-grass plains, mesquite savannas, and gypsum-hill regions; ecotone between short-grass plains and mixed prairie in Oklahoma (Bragg, 1950a,c; Black and Sievert, 1989); arid and semiarid plains and grasslands in Texas (Garrett and Barker, 1987); and xerophilic brushland and grasslands in Mexico (Flores-Villela, 1993). Green toads often take refuge under rocks or in existing rodent or other burrows and may occur in grasslands that have been converted to agriculture where herbicide and/or pesticide levels do not exceed lethal limits.
F. Home Range Size. Unknown.
G. Territories. Territorial behavior other than during breeding aggregations is unknown. Generally only single individuals are encountered under rocks during the dry season. During breeding aggregations, calling males are usually separated by 0.5–3.0 m, however on occasion may call within 0.1 m of one another (Sullivan, 1984). Bogert (1962) and Sullivan (1984) provide information on advertisement call characteristics and variation.
H. Aestivation/Avoiding Dessication. Unknown. Green toads are not surface active unless sufficient moisture is available in the form of summer rainfall or unusually humid nights.
I. Seasonal Migrations. None reported.
J. Topor (Hibernation). Generally below ground and inactive September–May in southern New Mexico (personal observations). The period of seasonal inactivity is likely longer at higher elevations and shorter at southerly latitudes.
K. Interspecific Associations/Exclusions. Breeding associates in New Mexico are Great Plains toads (Bufo cognatus), western narrow-mouthed toads (Gastrophryne olivacea), Couch's spadefoot toads (Scaphiopus couchii), plains spadefoot toads (Spea bombifrons), Mexican spadefoot toads (S. multiplicata), and, marginally, American bullfrogs (Rana catesbeiana; Creusere and Whitford, 1976; Stuart and Painter, 1996). Bragg (1950a,b) reported Texas toads (B. speciosus), Woodhouse's toads (B. woodhousii), Couch's spadefoot toads, plains spadefoot toads, narrow-mouthed toads (Gastrophryne sp.), and tiger salamanders (Ambystoma tigrinum) as breeding associates in Oklahoma. Additional breeding associates include plains leopard frogs (R. blairi), northern cricket frogs (Acris crepitans; Kansas; Taggart, 1997a), and Colorado River toads (B. alvarius; Arizona; B.K. Sullivan, personal communication). Although predation by American bullfrogs has been reported (Stuart, 1995), it is unlikely that American bullfrogs would exclude green toads from an area.
L. Age/Size at Reproductive Maturity. Sullivan (B.K., personal communication) reported males in southwest New Mexico calling at 37 mm SVL (range 37–46 mm; n = 22); females found in amplexus ranged from 44–54 mm SVL (n = 6).
M. Longevity. Unknown. Fewer than 1% of the juveniles survive to adult size (Creusere and Whitford, 1976).
N. Feeding Behavior. No comprehensive study of the food habits of green toads has been published, although individuals likely feed on a variety of small arthropods and other invertebrates. Taggart (1997a) reported observing green toads feeding on small insects, especially Hymenoptera (ants) and small Lepidoptera, Coleoptera, and Orthoptera.
O. Predators. Little information is available on the predators of green toads. Known predators on adults and juveniles include American bullfrogs (Stuart, 1995), checkered garter snakes (Thamnophis marcianus; Stuart and Painter, 1996), plains garter snakes (T. radix), and tiger salamanders (Taggart, 1997a). Likely predators include western hog-nosed snakes (Heterodon nasicus), coachwhips (Masticophis flagellum), and gopher snakes (Pituophis catenifer; Creusere and Whitford, 1976). Eggs or tadpoles may be attacked by the fungus Saprolegnia sp. and by a host of invertebrate predators including Odonata (dragonfly larvae), Hemiptera (Notonectidae—backswimmers; Belostomatidae–giant water bugs), Coleoptera (Dytiscidae—predaceous diving beetles; Hydrophilidae—water scavenger beetles). Tadpoles and adults may also be preyed upon by black-necked garter snakes (T. cyrtopsis), ravens, raccoons, and skunks. Cei et al. (1968) report the presence of presumably toxic indolealklamines from the skin and paratoid glands of green toads. The high mortality rate of juveniles is likely accounted for by poor microhabitat selection (Creusere and Whitford, 1976).
P. Anti-Predator Mechanisms. Nocturnal and secretive, usually seeking shelter in underground burrows or beneath surface objects. Adults rarely are seen except during the breeding season. Adults in breeding choruses are quick to retreat underwater or into surrounding vegetation at slight disturbance. Parotoid glands produce cardiotoxic steroids, possibly rendering the species unpalatable to some predators (Duellman and Trueb, 1986).
Q. Diseases. Unknown. Malformations in green toads have not been reported by the North American Reporting Center for Amphibian Malformations (Northern Prairie Wildlife Research Center, 1997).
R. Parasites. Metcalf (1923) reported an unknown species of Opalinidae (Protoza) from 11% of the green toads examined from Texas. McAllister et al. (1989) reported the following endoparasites from a series of 27 green toads collected in north-central Texas: Nyctotherus cordiformis (Protoza); Myxidium serotinum (Myxozoa); Istoichometra bufonis (Cestoidea); and Cosmoceroides variabilis (Nematoda). All blood samples were negative for Apicomplexa or trypanosomes, and no Protoza were found. Goldberg et al. (1995) found 98% of 49 green toads examined from Doña Ana County, New Mexico, harbored helminths including the cestoid Distoichometra bufonis and the nematodes Aplecctana incerta, A. itzocanenis, Rhabdias americanus, and Physaloptera sp.
4. Conservation. The current distribution of green toads is thought to be similar to the historical distribution. Their historical abundance is unknown, however localized populations have likely declined due to the disappearance of habitat, especially wetlands. Green toads are localized, but common in remaining areas of suitable habitat. They are listed as Protected by Kansas.
1Charles W. Painter
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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