Gastrophryne olivacea (Hallowell, 1857 "1856")
Western Narrow-Mouthed Toad
Michael J. Sredl1
Kimberleigh J. Field2
1. Historical versus Current Distribution. Western narrow-mouthed toads (Gastrophryne olivacea) are found in the north from central Missouri along the Missouri River valley and extreme southern Nebraska, south through most of Kansas, Oklahoma, Texas (with the exception of the northern portion of the panhandle and western extremes), and the Mexican Plateau. Disjunct populations occur in the Oklahoma Panhandle, southeastern Colorado, western Kansas, central Arkansas, southwestern New Mexico, northeastern New Mexico, and south-central Arizona (Wright and Wright, 1949; Metter et al., 1970; Collins, 1979; Hammerson, 1980; Neck, 1980a; Price and Price, 1991; Moriarty et al., 2000). Arizona animals are sometimes considered to be a separate subspecies (Stebbins, 1985). Bogert and Oliver (1945) suggest that western narrow-mouthed toads are excluded from California by desert habitats.
Metter et al. (1970) noted that the range of western narrow-mouthed toads in Kansas had expanded into central Kansas along the Missouri River. Blair (W.F., 1955b) observed that as more land in Texas is converted to agriculture, the range of western narrow-mouthed toads should increase.
Sullivan et al. (1996b) surveyed Arizona populations of western narrow-mouthed toads and found them to be present at most historical localities except those on the eastern margin of their Arizona range.
2. Historical versus Current Abundance. Little is known of historical abundance of western narrow-mouthed toads, and comments on historical abundance are largely anecdotal. Bragg (1941) noted that western narrow-mouthed toads were historically “common and numerous in all parts of Oklahoma. [They are] especially abundant in the prairies and in the oak-hickory savanna areas.” Data collected by Bragg (1960b) showed that between 1935–'59, populations of western narrow-mouthed toads near Norman, Oklahoma, appeared to be stable. Similarly, Fitch (1956a), using data collected in Kansas, noted that they were one of the most numerous vertebrates and had a biomass that often exceeded that of larger vertebrates. No studies of current abundance for this species have been published.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Migration to breeding ponds is stimulated by rains > 5 cm (Bragg, 1943b; Stebbins, 1954a; Fitch, 1956a), which fill temporary ponds and moisten the earth for overland migration (Fitch, 1956a). Choruses build up rapidly, followed by dwindling activity (Blair, 1961a). Frogs appear to travel a different route when returning to their home range after breeding, perhaps because conditions are drier than those that prevailed during the pondward trip (Fitch, 1956a). Warm rains appear key in initiating reproductive activity, and air and water temperatures below 18.0 ˚C inhibit breeding (Wiest, 1982).
Breeding takes place from mid March to September in Texas (Wright and Wright, 1949; Blair, 1961a), but is more restricted farther north (Smith, 1934; Bragg, 1943b; Fitch, 1956a; see also Nelson, 1972a). Rainfall patterns in the southwestern United States may restrict breeding in this area.
ii. Breeding habitat. Western narrow-mouthed toads utilize permanent and temporary aquatic systems for breeding and have been observed to breed in springs, temporary rain pools, stock ponds, flooded fields, and drainage and roadside ditches (Wright and Wright, 1949; Stebbins, 1954a; Fitch, 1956a; Jameson, 1956a; Metter et al., 1970). Site fidelity may be high. In central Texas, western narrow-mouthed toads returned to the same breeding pond 2 yr in a row (Jameson, 1956a).
When males arrive at the breeding pond, they call from the margins of the pond while hidden in grass hillocks, next to roots of trees, or near bases of large rocks. If they are submerged, only their head protrudes above the water surface (Bragg, 1943b; Stebbins, 1951; Stuart and Painter, 1996). Some males have been observed to call while floating (similar to spadefoot toads), but most maintain an upright posture while calling in shallow water (Stebbins, 1951; Nelson, 1973; Stuart and Painter, 1996). Bragg (1943b) observed that males often clumped at the breeding pond and suggested they were attracted to the calls of one another. Most calling is done at night and usually ceases or is greatly reduced toward midnight or slightly later (Freiburg, 1951), but males may call during the day when breeding is at its peak (Fitch, 1956a).
The call of western narrow-mouthed toads has been described as “a very short peep followed by a buzz like that of an angry bee,” a “high, shrill buzz,” or “a short whit followed by a low nasal buzz” (Smith, 1934; Conant, 1975; Stebbins, 1985). A single call cannot be heard from > 30 m distance (Smith, 1934). A full chorus sounds like a band saw, a swarm of angry bees, or, from a distance, a flock of sheep (Smith, 1934; Stebbins, 1985). Amplexus is axillary and the male “glues” himself to the female using an adhesive produced by specialized secretory cells in the dermis of the venter (Fitch, 1956a). Clasping pairs float in water deeper than where males call, sometimes clinging to vegetation (Henderson, 1961). Males are known to breed at least twice in 1 yr; it is unknown if females breed more than once per year (Fitch, 1956a).
i. Egg deposition sites. Egg masses of western narrow-mouthed toads have been most frequently described as floating films (Livezey and Wright, 1947; Wright and Wright, 1949; Stebbins, 1951; Salthe, 1963), but occasionally masses may become attached to submerged leaves and stems of grasses and weeds or sink to the bottom of the pond (Livezey and Wright, 1947; Stebbins, 1951; Fitch, 1956a).
ii. Clutch size. Females can lay at least 650 eggs, and perhaps as many as 2,100 eggs (Livezey and Wright, 1947; Freiburg, 1951; Henderson, 1961), that form clusters of 100–200 (Stebbins, 1951). Water temperatures of oviposition sites in Texas ranged between 19.0–32.0 ˚C and averaged 24.9 ˚C (W.F. Blair, 1955b). Water temperature of an oviposition site in Arizona was 28.6 ˚C (Stebbins, 1951).
Laboratory experiments indicate that the lower lethal temperature limit of developing larvae is between 17.0–18.0 ˚C, while the upper lethal temperature limit is between 27.0–32.6 ˚C (Hubbs and Armstrong, 1961; Hubbs et al., 1963; Ballinger and McKinney, 1966) and may be as high as high as 38.9 ˚C (Ballinger and McKinney, 1966).
C. Larvae/Metamorphosis. Larvae hatch in 2 d (Wright and Wright, 1949; Fitch, 1956a).
i. Length of larval stage. Length of larval period reported is generally between 28–50 d (Bragg, 1947; Wright and Wright, 1949; Duellman and Trueb, 1986; see also Nelson, 1972a), although Fitch (1956a) reported larvae that transformed in 24 d in a Kansas pond. Tadpoles reach a maximum body length of 25 mm (Wright and Wright, 1949).
ii. Larval requirements. Western narrow-mouthed toad larvae can tolerate temperatures over 35 ˚C (Bragg, 1950e; Ballinger and McKinney, 1966).
a. Food. Because tadpoles lack keratinized mouthparts, they cannot graze on anything larger than can fit in their mouth (Hoff et al., 1999) and are restricted to filter feeding (Nelson, 1972b). No detailed study of tadpole diet has been conducted, but likely food items are small plants and animals that accumulate at the surface of the water (Stebbins, 1954a; Altig and Kelly, 1974).
b. Cover. Tadpoles have been observed to float motionless near the surface of the water (Bragg, 1947b; Stuart and Painter, 1996). The significance of this behavior, if any, is unknown.
iii. Larval polymorphisms. None reported.
iv. Features of metamorphosis. Western narrow-mouthed toads metamorphose from mid April to October (Wright and Wright, 1949; Fitch, 1956a; Duellman and Trueb, 1986). Size at metamorphosis and average adult body size vary geographically (Nelson, 1972b). Wright and Wright (1949) report size at metamorphosis of 10–12 mm for the species. Fitch (1956a) reports a size at metamorphosis of 15–16 mm, rarely as small as 14.5 mm for Kansas frogs.
v. Post-metamorphic migrations. Fitch (1956a) observed that juvenile western narrow-mouthed toads disperse widely. In years when juveniles were unable to disperse from breeding ponds because of drought, predation took a heavy toll (Fitch, 1956a).
D. Juvenile Habitat. Little is known of juvenile habitat characteristics, but they are likely similar to those of adults. Following post-metamorphic migrations in Kansas, juveniles were found in a variety of habitat types (Fitch, 1956a).
E. Adult Habitat. Western narrow-mouthed toads are terrestrial, nocturnal, and secretive. They are usually found in burrows and in retreats such as rocks, mud cracks, tree bark and roots, logs, and litter, usually near the vicinity of water (Dickerson, 1906; Smith, 1934; Wright and Wright, 1949; Stebbins, 1954a; Fitch, 1956a). Conant (1975) succinctly described their habitat needs as anywhere where there is “shelter and moisture.”
Freiburg (1951) found that western narrow-mouthed toads used rocks of varying sizes as cover, with the usual choice being a flat rock approximately 8 cm thick and 50 cm in diameter. Rocks that were in groups were more often frequented than isolated rocks. Average soil moisture measured between early June and early August at five rock shelters varied between 9–29% (Freiburg, 1951).
While not usually active during the day, Fitch (1956a) recorded a body temperature of 37.6 ˚C for one western narrow-mouthed toad. This temperature was taken from a frog that “froze” and remained motionless in the sunshine for 30 s after the rock sheltering it was overturned. It is among the highest body temperatures recorded for any anuran (Hutchison and Dupré, 1992).
Throughout their range, western narrow-mouthed toads are found in varied habitats. In general, these habitats are considered prairies and open woodlands (Nelson, 1972b). In Arizona, they are found from desert grasslands to oak woodland habitats (Jones et al., 1983; Stebbins, 1985). Oklahoma and Kansas habitats are described as flood plains, prairies, and deciduous forests (Bragg, 1941; Blair, 1950e; Fitch, 1956a). Elevational ranges of western narrow-mouthed toads is reported from sea level to 1,250 m (Stebbins, 1985).
F. Home Range Size. Some have suggested that western narrow-mouthed toads do not have well-defined home ranges and seem to wander in any direction where suitable habitat is encountered (Freiburg, 1951). Fitch (1956a) suggested that toads become familiar with an area and the available shelters within it, yet may shift their home ranges throughout their lives. In a Kansas population, the typical home range size was approximated to be 22 m in radius, and males tended to travel farther than did females (Fitch, 1956a).
G. Territories. Males will produce a call that differs from the breeding call. This call appears to be agonistic because it is used in establishing territories (Dayton, 2000b).
H. Aestivation/Avoiding Dessication. Aestivation has not been reported, but western narrow-mouthed toads are known to spend long periods of inactivity in subterranean retreats during droughts (Dickerson, 1906; Wright and Wright, 1949; Freiburg, 1951; Fitch, 1956a; Blair, 1961a; Bragg, 1965; Sullivan, 1996).
I. Seasonal Migrations. Seasonal movements by western narrow-mouthed toads occur during the breeding season. In Kansas, toads moved to breeding ponds during rains. Interestingly, they may take different routes when moving toward and away from breeding ponds. The change in route is likely necessitated by the drier conditions when leaving the pond as compared to the rainstorms when arriving (Fitch, 1956a). In winter, western narrow-mouthed toads are not likely to be found in their usual spots after the first frost, but may have moved to deeper subterranean sites (Fitch, 1956a) rather than migrating out of their active season home range areas.
J. Torpor (Hibernation). While many have commented on the subterranean habits of western narrow-mouthed toads, hibernation has not been studied in detail. Fitch (1956a) noted that western narrow-mouthed toads hibernated between mid October and early May in Kansas. Freiburg (1951) found that in March and April the few western narrow-mouthed toads that could be found were always discovered under the most massive rocks in the area, which may possibly serve as hibernacula.
K. Interspecific Associations/Exclusions. Western narrow-mouthed toads have been reported to occur with numerous temporary and permanent pond breeding amphibians, including Mexican burrowing toads (Rhinophrynus dorsalis), plains spadefoot toads (Spea bombifrons), New Mexico spadefoot toads (Spea multiplicatus), Couch’s spadefoot toads (Scaphiopus couchii), eastern spadefoot toads (Scaphiopus holbrookii), Sonoran Desert toads (Bufo alvarius), Great Plains toads (B. cognatus), green toads (B. debilis), Sonoran green toads (B. retiformis), Texas toads (B. speciosus), southern toads (B. terrestris), Gulf Coast toads (B. nebulifer), Woodhouse’s toads (B. woodhousii), northern cricket frogs (Acris crepitans), canyon treefrogs (Hyla arenicolor), eastern gray treefrogs (H. versicolor), spotted chorus frogs (Pseudacris clarkii), spring peepers (Pseudacris crucifer), Strecker’s chorus frogs (P. streckeri), upland chorus frogs (P. feriarum), northern casque-headed frogs (Pternohyla fodiens), plains leopard frogs (Rana blairi), Rio Grande leopard frogs (R. berlandieri), American bullfrogs (R. catesbeiana), green frogs (R. clamitans), southern leopard frogs (R. sphenocephala), lowland leopard frogs (R. yavapaiensis), eastern narrow-mouthed toads (Gastrophryne carolinensis), and sheep frogs (Hypopachus variolosus; Dickerson, 1906; Campbell, 1934; Wright and Wright, 1949; Jameson, 1950a, 1956a; Freiburg, 1951; Lindsay, 1954; Minton, 1959; Blair, 1961a; Wake, 1961; Bragg, 1965; Wiest, 1982; Jones et al., 1983; Stuart, 1995; Stuart and Painter, 1996; Altig et al., 1998).
Western narrow-mouthed toads hybridize with eastern narrow-mouthed toads and sheep frogs (Nelson, 1972a). Of particular interest have been zones of sympatry between western narrow-mouthed toads and eastern narrow-mouthed toads. The principal isolating mechanisms between these taxa appear to be (1) habitat differences and (2) call differences (W.F. Blair, 1955b). In the zone of sympatry, eastern narrow-mouthed toads are usually found in the more mesic, forested habitats. Blair (W.F., 1955b) studied calls from localities throughout the range of these species and found that calls from the overlap zone differed to the greatest degree. Blair (W.F., 1955b) noted that clearing land for agriculture in the overlap zone may create more xeric habitat, thereby allowing western narrow-mouthed toads to expand their range and replace eastern narrow-mouthed toads.
Interactions between western narrow-mouthed toads and other anuran species have been less studied. Most attention has been paid to breeding phenology (Blair, 1961a; Wiest, 1982). Licht (1967a) describes inhibition of western narrow-mouthed toad tadpoles’ growth and even death due to the presence of tadpoles of other genera in laboratory experiments.
Western narrow-mouthed toads have been found in burrows with eastern moles (Scalopus aquaticus), collared lizards (Crotaphytus collaris), common five-lined skinks (Eumeces fasciatus), great plains skinks (E. obsoletus), and tarantulas (Blair, 1936; Freiburg, 1951; Hunt, 1980; McAllister and Tabor, 1985). Of the tarantula burrows checked (n = 100), 75% had from 1–3 western narrow-mouthed toads in them (Blair, 1936). Western narrow-mouthed toads may derive protection from tarantulas, while tarantulas may benefit from having their nests kept free of ants (Hunt, 1980).
L. Age/Size at Reproductive Maturity. Western narrow-mouthed toads reach sexual maturity at 1–2 yr of age; adult sizes range between 19–42 mm (Wright and Wright, 1949; Fitch, 1956b; Stebbins, 1985; Duellman and Trueb, 1986). Size varies geographically (W.F. Blair, 1955a; Nelson, 1972a). The best indicator of a sexually mature male is the presence of a dark, distensible throat pouch (Fitch, 1956a; Degenhardt et al., 1996).
M. Longevity. Western narrow-mouthed toads have been documented to live as long as 7–8 yr in the wild, although only an extremely small percentage do so (Fitch, 1956b).
N. Feeding Behavior. Western narrow-mouthed toads, once referred to as “ant-eating frogs,” are indeed ant specialists (Nelson, 1972b; Behler and King, 1998); adults will live next to ant colonies (Tanner, 1950; Fitch, 1956a; see also Nelson, 1972a). In addition to ants, beetle remains have been found in their feces (Freiburg, 1951). The pointed head and leathery skin that is characteristic of western narrow-mouthed toads is typical of other fossorial, ant specialists in the family Microhylidae (Nelson, 1972b).
O. Predators. Anuran predators of western narrow-mouthed toads are American bullfrogs and leopard frogs (R. pipiens complex). Increased reproductive success has been linked to decreased numbers of bullfrogs and leopard frogs in breeding ponds (Fitch, 1956a). Documented snake predators of the western narrow-mouthed toad include northern water snakes (Nerodia sipedon), common garter snakes (Thamnophis sirtalis), western ribbon snakes (Thamnophis proximus), checkered garter snakes (Thamnophis marcianus), and copperheads (Agkistrodon contortrix; Freiburg, 1951; Clark, 1974; Stuart and Painter, 1996). Short-tailed shrews (Blarina brevicauda) are also thought to prey on western narrow-mouthed toads and may be capable of eating a dozen western narrow-mouthed toads in one night (Freiburg, 1951).
P. Anti-Predator Mechanisms. Crypticity, movements, and skin secretions are all used by western narrow-mouthed toads to avoid predators. If hiding cover is removed, western narrow-mouthed toads frequently will remain motionless until further disturbed. Escape movements are sporadic, yet not always swift. The western narrow-mouthed toad’s “gait is a combination of running and short hops that are usually only an inch or two in length” (Fitch, 1956a). By changing directions many times and easily finding cover, the toad may be able to escape from a predator. At other times, western narrow-mouthed toads have been seen to crawl through grasses in a fast, mouse-like fashion (Wright and Wright, 1949). Once captured, the toad’s slippery (Fitch, 1956a), irritating, and distasteful (Conant, 1975) dermal secretions give it yet another chance for escape. When in water, they float with only the tips of their snouts above water and slip beneath the water without leaving a ripple (Cope, 1889; Dickerson, 1906; Stebbins, 1951).
Q. Diseases. None reported.
R. Parasites. Western narrow-mouthed toads have been found to be infected with myxosporeans (Myxidium serotinum), coccidians (Isospora fragusum), nematodes (Cosmocercoides dukae, Aplectana itzocanensis), cestodes (Cylindrotaenia americana), and chiggers (Freiburg, 1951; Nelson, 1972a; McAllister and Upton, 1987a; Upton and McAllister, 1988; McAllister and Trauth, 1995; Goldberg et al., 1998a). McAllister and Upton (1987a) checked western narrow-mouthed toads for hematozoans, but found none (n = 63). They appear to have a resistance to Saprolegnia sp. fungus (Bragg, 1962a).
4. Conservation. Sullivan et al. (1996b) surveyed Arizona populations of western narrow-mouthed toads and found them to be present at most historical localities except those on the eastern margin of their Arizona range. Nevertheless, western narrow-mouthed toads are included on the Arizona Department of Game and Fish's list of Threatened Native Wildlife as a Candidate species (J.E. Wallace at www.gf.state.az.us). Western marrow-mouthed toads are also listed as a Species of Special Concern in Colorado (http://wildlife.state.co.us) and are given Endangered status in New Mexico (www.nmcpr.state.nm.us).
More optimistically, Metter et al. (1970) noted that the range of western narrow-mouthed toads has expanded into central Kansas along the Missouri River, and Blair (W.F., 1955b) hypothesized that as more land in Texas is converted to agriculture, the range of western narrow-mouthed toads should increase.
1Michael J. Sredl
Arizona Game and Fish Department
2221 West Greenway Road
Phoenix, Arizona 85023-4399
2Kimberleigh J. Field
Arizona Game and Fish Department
2221 West Greenway Road
Phoenix, Arizona 85023-4399
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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