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Plains Spadefoot - Spea bombifrons

Native Species

Global Rank: G5
State Rank: S4
(see State Rank Reason below)

Agency Status


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Copyright by Bill Preston, Manitoba Museum of Man and Nature
State Rank Reason (see State Rank above)
Recent nocturnal calling surveys conducted after precipitation events on warm evenings have often detected this species east of the Continental Divide. It appears that the previous perception of rarity was due in part to lack of historical survey effort and difficulty detecting the species during much of the year and in most weather conditions. Given these data, the SOC status can no longer be justified and the rank has been increased to S4.
  • Details on Status Ranking and Review
    Plains Spadefoot (Spea bombifrons) Conservation Status Review
    Review Date = 05/03/2018
    Range Extent

    ScoreG - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)

    Comment282,342 square Kilometers from Natural Heritage Program range maps

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentAs the species uses pasture and some agricultural lands, habitat has likely been relatively stable since European arrival

    Short-term Trend

    ScoreE - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation

    CommentSpecies appears to be stable based on repeated detections at some sites.


    ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.

    CommentMortality on roads, contamination of breeding sites with agricultural chemicals or fecal matter from cows, irrigated fields functioning as ecological traps

    SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.

    CommentAny degradation of habitat or decline in population would likely be reversible within a few decades

    ScopeModerate - 20-60% of total population or area affected

    CommentThreats exist across much of this species range

    ImmediacyHigh - Threat is operational (happening now) or imminent (within a year).


    Intrinsic Vulnerability

    ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).

    CommentHigh fecundity, relatively low age of maturity

    Environmental Specificity

    ScoreC - Moderate. Generalist. Broad-scale or diverse (general) habitat(s) or other abiotic and/or biotic factors are used or required by the species but some key requirements are scarce in the generalized range of the species within the area of interest.

    CommentSpecies requires ephemeral waterbodies and specific soil types. Both are found across much of eastern and central Montana

    Raw Conservation Status Score

    Score 3.5 + 0 (geographic distribution) + 0 (environmental specificity) + 0 (short-term trend) + 0 (threats) = 3.5

General Description
Laid in small clusters of 10-250 totaling up to 3,844 eggs per female (Mabry and Christiansen 1991). Each ovum is dark brown or black above, pale yellow to white below, and is surrounded by three jelly layers (two thin layers immediately adjacent to the ovum and a thicker outer layer) (Hoyt 1960). Ovum diameters are approximately 1.5 mm (0.6 in), but total egg diameters, including the three jelly layers, are approximately 3 mm (0.12 in) (Hoyt 1960).

Light gray or brown dorsally and lighter iridescent golden ventrally (Hammerson 1999). The gut coil is not visible through the body wall. The tail fin is clear with sparse yellow flecks and the anus is at the base of the tail on the midline. The body shape is globular with eyes located dorsally. The mandibles are frequently cusped; labial tooth rows are 0/0 to 6/6, but most often 3/4 or 4/4. Oral papillae completely encircle the mouth. Total length (TL) of 9-68 mm (0.35-2.68 in) (Russell and Bauer 2000, Klassen 1998).

Base color is white ventrally and ranges from light brown to dull green dorsally. The back may be covered with smallish tubercles tipped in yellow or orange, and often present as a rough hourglass-shaped marking. Four lighter stripes are usually present laterally, but some individuals have indistinct longitudinal streaking (Hammerson 1999). Pupil of the eye is vertically elongated in bright light. A large and usually bony bump or boss is present between the eyes (Hall 1998). A single hard and dark wedge-shaped digging “spade” is present on the soles of the hind feet. Males have dark patches on the inner 2-3 digits of the forelimbs during breeding and have an expanded bi-lobed vocal sac. The male breeding call is a brief snore. Snout-vent length (SVL) of 10-60 mm (0.39-2.4 in) (Hammerson 1999, Klassen 1998).

Calls are short (1 second) and flat nasal snores repeated for extended periods (Werner et al. 2004). The calls are loud and can carry a distance up to 1600 meters (5,250 ft) (Bryce Maxell, personal communication).

Diagnostic Characteristics
No other adult frogs or toads known to inhabit Montana have a rounded bony boss directly between the eyes or a vertical eye pupil. Plains Spadefoot (Spea bombifrons) do not have prominent parotoid glands posterior to the eyes like toads. Larvae of the Western Toad (Anaxyrus boreas), Great Plains Toad (Anaxyrus cognatus), and Woodhouse’s Toad (Anaxyrus woodhousii) are all dark dorsally. Larvae of Columbia Spotted Frog (Rana luteiventris) and Northern Leopard Frog (Lithobates pipiens) are much more mottled in color with gold and black flecking. See species accounts for more information. The Great Basin Spadefoot (Scaphiopus inermontanus) is known from southeastern Idaho and may occur in southwestern Montana; it has a low and pliable lump between the eyes, while the Plains Spadefoot's lump is high and hard.

Species Range
Montana Range Range Descriptions


Western Hemisphere Range


Range Comments
There is currently some debate as to whether the plains spadefoot and other western spadefoots should be placed in the genus Spea or Scaphiopus (Hall 1998). However, regardless of the generic name, a single distinct species is recognized as ranging across the Great Plains from northern Mexico to southern Canada at elevations up to 2,440 m (8,000 ft) (Stebbins 2003, Wiens and Titus 1991). In Montana they have been sparsely documented across the eastern plains and at a handful of locations in the mountain valleys of the upper Missouri watershed at elevations up to 1,524 m (5,000 ft).

Maximum elevation: 2,014 m (6,608 ft) near the Madison Arm of Hebgen Reservoir in Gallatin County (Ryan DeKnikker and Nichole Walker, MTNHP 2008).

Observations in Montana Natural Heritage Program Database
Number of Observations: 853

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

No information specific to Montana Plains Spadefoot is available. Elsewhere adults are known to migrate up to several hundred meters between breeding pools and nonbreeding terrestrial habitats. During breeding, they may move 60-150 m (197-492 ft) during each night as they leave the breeding ponds and move inland (Hammerson 1999).

Little specific habitat information is available. This species is usually found in areas with soft sandy/gravelly soils in native grasslands and shrublands as well as pastures and hay lands with non-native vegetation (Lauzon and Balagus 1998). These sites are typically located near permanent or temporary bodies of water. For much of each year it lives largely inactive in burrows of its own construction or occupies rodent burrows and enters water only to breed Ttadpoles and toadlets have been observed in stock ponds and small ephemeral reservoirs, usually in sagebrush-grassland habitats (Cope 1879, Mosimann and Rabb 1952, Dood 1980, Reichel 1995b, Hendricks 1999a, Hossack et al. 2003).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
Food habits in Montana have not been studied. Tadpoles commonly have two morphologies, omnivores and carnivores. Omnivorous larvae eat suspended matter, organic debris, algae, and plant tissue. While carnivorous larvae are predatory and eat relatively large aquatic invertebrates, such as fairy shrimp and insect larvae, as well as other amphibian larvae, including their own species (Bragg 1964, Pfenning 1990, Hammerson 1999). Metamorphosed Plains Spadefoot in Colorado eat various small terrestrial arthropods, including spiders, terrestrial amphipods, snails, earthworms, centipedes, and nine orders of insects, but seem to rely on lepidopterans, coleopterans, and homopterans to a greater extent (Kellog 1932, Whitaker et al. 1977), and rarely small vertebrates (Hammerson 1999). In the playa wetlands of northwest Texas, carabid beetles were the most common food (Anderson et al. 1999).

Adult Plains Spadefoots are mostly on the surface on warm nights during damp and dry weather when air temperatures are between 12 and 26 °C (54-79 °F) (Kellog 1932, Whitaker et al. 1977). Adults in Alberta, Wyoming, and Colorado may be active anytime during May through August and less frequently later (Baxter and Stone 1985, Russell and Bauer 1993, Klassen 1998, Hammerson 1999), depending on rains and the presence of standing water. In Montana, adults have been observed during May to August (Mosimann and Rabb 1952, Hendricks 1999a, Hossack et al. 2003). Adults retreat to burrows excavated by digging backwards using the spades on the hind feet until pockets of moist soil are encountered, sometimes at depths of almost a meter (Russell and Bauer 2000). Juveniles and adults are known to disperse at least 2.25 km (1.4 mi) from breeding ponds (Klassen 1998). Tadpoles may be able to tolerate brief periods (>20 hours) of almost total evaporation of their pools (Moore 1937, Black 1974b, Russell and Bauer 1993).

Predators of adults and juveniles include birds such as Swainson's Hawk (Buteo swainsoni), Burrowing Owl (Athene cunicularia), Black-crowned Night-Heron (Nycticorax nycticorax), and Prairie Rattlesnake (Crotalus viridis). Tadpole predators include gartersnakes (Thamnophis), the tadpole shrimp (Triops sp.), and cannibal Plains Spadefoot tadpoles (Baxter and Stone 1985, Hammerson 1999). Predators in Montana are not reported. Threatened adults inflate with air and squat with the head bent downward, and often release fluid from the vent if handled; large tadpoles may produce a clicking sound with their mouthparts if removed from water (Hammerson 1999).

Reproductive Characteristics
Adults probably reach maturity when 2 to 3 years old. Iowa males are mature when 3.1-3.8 cm (1.2-1.5 in) SVL and females when 3.2-4.0 cm (1.3-1.6 in) SVL. Breeding adults in Colorado are typically 4.0-6.0 cm (1.6-2.4 in) SVL (Hammerson 1999). Breeding occurs in Colorado after heavy rains of 1.8 cm (0.71 in) or more at air temperatures greater than 10 °C (50 °F). (Hammerson 1999). Choruses usually last about 2 or 3 days from late May through early August. Adults call from edges of pools or while floating; large choruses can be heard from a distance of 3 km (1.9 mi) or more. Adults usually leave the water once breeding and egg-laying are finished but may remain nearby for several days if rain continues. Rains occurring after the first round of breeding may stimulate more breeding, presumably from individuals that did not breed the first time. Breeding takes place in warm, often muddy, temporary water bodies (Klassen 1998). Adults have been reported in water up to 30 cm (11.8 in) deep in flooded wagon wheel ruts, temporary rain pools formed in wide flat-bottom coulees, water tanks, and badland seep ponds (Cope 1879, Mosimann and Rabb 1952, Dood 1980, Reichel 1995b, Hendricks 1999a, Hossack et al. 2003).

Females lay up to 2700 eggs during a single breeding event, often in several egg masses. Eggs are deposited on rocks, submerged vegetation, or loose on the bottom of the pool, and hatch in 2-3 days (Hammerson 1999). Depending on conditions, transforming toadlets emerging from the water may still have tails. Tadpoles that are carnivorous morphs reach metamorphosis much sooner than omnivorous morphs (Gilmore 1934, Bragg 1964). Time to metamorphosis can vary depending on location. In Colorado, metamorphosis can take from 21 to more than 75 days (Hammerson 1999); while in Alberta, metamorphosis was a minimum of 21 to 34 days and a maximum of more than 60 days (Klassen 1998). In Montana, tadpoles in various stages (legless to 4-legged) have been reported during late June of the same year in Carbon County (Hendricks 1999a), and fully transformed juveniles have been found in the same area during a different year in late August (Maxell et al. 2003). Recently transformed juveniles have been reported along the Missouri River in late August (Cope 1879).

The following was taken from the Status and Conservation section for the Plains Spadefoot account in Maxell et al. 2009

In the past 125 years Plains Spadefoots have only been documented at about 40 localities across the plains and in the mountain valleys east of the Continental Divide and at the present time their status across this region is almost completely unknown. Risk factors relevant to the viability of populations of this species are likely to include grazing, road and trail development, on- and off-road vehicle use, use of pesticides and herbicides, development of water impoundments, habitat loss/fragmentation, and metapopulation impacts, all as described above. However, the lack of information on the distribution, status, habitat use, and basic biology of the species may currently represent the greatest risk to the viability of the species (i.e., the species could have undergone, or currently be undergoing, drastic declines but we lack any kind of baseline information that would allow us to make such a determination). Individual studies that specifically identify risk factors or other issues relevant to the conservation of Plains Spadefoots include the following. (1) At least two reports indicate that non-intensive agriculture may be compatible with the survival of Plains Spadefoot populations. Lauzon and Balagus (1998) found them breeding in wetlands adjacent to improved pasture and hay lands comprised almost completely of non-native vegetation. Klassen (1998) found Plains Spadefoots breeding in temporary pools that formed in native grasslands used as cattle pastures and some of these pools were fouled with cattle manure. However, Bragg (1937b) reports that all the Plains Spadefoot eggs in pools that were heavily contaminated with fecal material from cattle died while other eggs in nearby uncontaminated pools survived. Klassen (1998) also reports that males called from a number of regularly irrigated cultivated fields and found them successfully breeding in one. Klassen (1998) indicated that irrigation may positively benefit populations by allowing regular reproduction in some areas. However, it is also conceivable that some irrigated areas may act as population sinks by drawing animals into areas where they may be impacted by agricultural chemicals or plowing which could disturb individuals in their burrows. (2) Both Bragg (1944) and Hammerson (1999) note that large numbers of Plains Spadefoots are killed on roads adjacent to breeding sites. (3) Hammerson (1999) notes that several populations have been extirpated due to residential and commercial development near Fort Collins, Colorado. (4) In a study of a congeneric species, Couch’s Spadefoot (Scaphiopus couchii), Judd (1977) found that the herbicide monosodium methanearsonate killed 86 percent of juvenile toads when they were exposed to only one eighth of the concentration recommended for agricultural spraying. The relationship of this herbicide to commonly applied herbicides in Montana is not known, but it is likely that both herbicides and pesticides may represent a threat to Plains Spadefoot populations. (5) Sounds from off-road vehicles have apparently been found to impact the emergence of congeneric Couch’s Spadefoots from their underground burrows (Bondello and Brattstrom 1979).

  • Literature Cited AboveLegend:   View Online Publication
    • Anderson, A. M., D. A. Haukos, and J. T. Anderson. 1999. Diet composition of three anurans from the playa wetlands of northwest Texas. Copeia 1999:515-520.
    • Baxter, G.T. and M.D. Stone. 1985. Amphibians and reptiles of Wyoming. Second edition. Wyoming Game and Fish Department. Cheyenne, WY. 137 p.
    • Black, J.H. 1974b. Larval spadefoot survival. Journal of Herpetology 8(4): 371-373.
    • Bondello, M.C. and B.H. Brattstrom. 1979. The effect of motorcycle sounds on the emergence of Couch's spadefoot toad, Scaphiopus couchi. Unpublished Report. U.S. Bureau of Land Management, California Desert Program, Riverside, California. Contract CA-060-CT7-2737. 27 p.
    • Bragg, A.N. 1937b. Observations on Bufo cognatus with special references to breeding habits and eggs. American Midland Naturalist 18: 273-284.
    • Bragg, A.N. 1944. The spadefoot toads in Oklahoma with a summary of our knowledge of the group. American Naturalist 78: 517-533.
    • Bragg, A.N. 1964. Further study of predation and cannibalism in spadefoot tadpoles. Herpetologica 20(1): 17-24.
    • Cope, E. D. 1879. A contribution to the zoology of Montana. American Naturalist 13(7): 432-441.
    • Dood, A.R. 1980. Terry Badlands nongame survey and inventory final report. Montana Department of Fish, Wildlife, and Parks and Bureau of Land Management, Helena, MT. 70 pp.
    • Gilmore, R.J. 1934. The tadpole of the spadefoot toad. Journal of the Colorado-Wyoming Academy of Science 1(6): 76
    • Hall, J.A. 1998. Scaphiopus intermontanus. Catalogue of American Amphibians and Reptiles 650.1-650.17.
    • Hammerson, G.A. 1999. Amphibians and reptiles in Colorado. University Press of Colorado & Colorado Division of Wildlife. Denver, CO. 484 p.
    • Hendricks, P. 1999a. Amphibian and reptile survey of the Bureau of Land Management Miles City District, Montana. Montana Natural Heritage Program, Helena, MT. 80 p.
    • Hossack, B., D. Pilliod, and S. Corn. 2003. Amphibian survey of Medicine Lake National Wildlife Complex: 2001-2002. USGS Northern Rocky Mountain Science Center, Aldo Leopold Wilderness Research Institute, Missoula, Montana. 19 p.
    • Hoyt, D.L. 1960. Mating behavior and eggs of the Plains spadefoot. Herpetologica 16: 199-201.
    • Judd, F.W. 1977. Toxicity of monosodium methanearsonate herbicide to Couch's spadefoot toad, Scaphiopus couchi. Herpetologica 33: 44-46.
    • Kellog, R. 1932. Notes on the spadefoot of the western plains (Scaphiopus hammondii). Copeia 1932(1): 36.
    • Klassen, M.A. 1998. Observations on the breeding and development of the plains spadefoot (Spea bombifrons) in southern Alberta. Canadian Field Naturalist 112(3): 387-392.
    • Lauzon, R.D. and P. Balagus. 1998. New records from the northern range of the plains spadefoot toad (Spea bombifrons) in Alberta. Canadian Field Naturalist 112: 506-509.
    • Mabry, C.M. and J.L. Christiansen. 1991. The activity and breeding cycle of Scaphiopus bombifrons in Iowa. Journal of Herpetology 25(1): 116-119.
    • Maxell, B.A., J.K. Werner, P. Hendricks, and D.L. Flath. 2003. Herpetology in Montana: a history, status summary, checklists, dichotomous keys, accounts for native, potentially native, and exotic species, and indexed bibliography. Society for Northwestern Vertebrate Biology, Northwest Fauna Number 5. Olympia, WA. 135 p.
    • Maxell, B.A., P. Hendricks, M.T. Gates, and S. Lenard. 2009. Montana amphibian and reptile status assessment, literature review, and conservation plan, June 2009. Montana Natural Heritage Program. Helena, MT. 643 p.
    • Moore, G.A. 1937. The spadefoot toad under drought conditions. Copeia 1937(4): 225-226.
    • Mosimann, J.E. and G.B. Rabb. 1952. The herpetology of Tiber Reservoir Area, Montana. Copeia(1): 23-27.
    • Pfenning, D.W. 1990. The adaptive significance of an environmentally-cued development switch in an anuran tadpole. Oecologia 85:101-107.
    • Reichel, J.D. 1995b. Preliminary amphibian and reptile survey of the Sioux District of the Custer National Forest: 1994. Montana Natural Heritage Program, Helena, MT. 75 p.
    • Russell, A. P. and A. M. Bauer. 1993. The amphibians and reptiles of Alberta. University of Calgary Press. Calgary, Alberta. 264 p.
    • Russell, A. P. and A. M. Bauer. 2000. The Amphibians and Reptiles of Alberta: A field guide and primer of boreal herpetology. University of Calgary Press, Toronto, Ontario. 279 p.
    • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. 3rd Edition. Houghton Mifflin Company, Boston and New York. 533 p.
    • Whitaker, J.A., Jr., D. Rubin and J.R. Munsee. 1977. Observations on food habits of four species of spadefoot toads, genus Scaphiopus. Herpetologica 33(4): 468-475.
    • Wiens, J.J. and T.A. Titus. 1991. A phylogenetic analysis of Spea (Anura: Pelobatidae). Herpetologica 47(1): 21-28.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
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    • Allen, J. A. 1874. Notes on the natural history of portions of Dakota and Montana Territories, being the substance of a report to the Secretary of War on the collections made by the North Pacific Railroad Expedition of 1873. Proceedings of the Boston Society of Natural History. pp. 68-70.
    • Atkinson, E.C. and M.L. Atkinson. 2004. Amphibian and reptile survey of the Ashland and Sioux of the Custer National Forest with special emphasis on the Three-Mile Stewardship Area:2002. Marmot's Edge Conservation. 22 p.
    • Bauer, Delane, 2002, 2002 Four Seasons Wildlife Study. Savage Mine Report, Richland County, Montana.
    • Black, J.H. 1973. Ethoecology of Scaphiopus (Pelobatidae) larvae in temporary pools in central and southwestern Oklahoma. Ph.D. Dissertation, University of Oklahoma. Norman, Oklahoma. 221 pp.
    • Blair, W.F. 1949. Development of the solitary spadefoot toad in Texas. Copeia 1949(1): 72.
    • Blair, W.F. 1955. Differentiation of mating call in spadefoots, genus Scaphiopus. Texas Journal of Science 7: 183-188.
    • Blair, W.F. 1956b. The mating call of hybrid toads. Texas Journal of Science 8: 350-355.
    • Blair, W.F. 1958b. Mating call in the speciation of anuran amphibians. American Naturalist 92: 27-51.
    • Boundy, J. 1992b. Spea bombifrons (Plains spadefoot). Herpetological Review 23(1): 25.
    • Bragg, A.N. 1941. Tadpoles of Scaphiopus bombifrons and Scaphiopus hammondii. Waserman Collector 4: 92-94.
    • Bragg, A.N. 1946. Aggregation with cannibalism in tadpoles of Scaphiopus bombifrons with some general remarks on the probably evolutionary significance of such phenomena. Herpetologica 3: 89-96.
    • Bragg, A.N. 1948a. Additional instances of social aggregations in tadpoles. Wassmann Collector 7: 65-79.
    • Bragg, A.N. 1956. Dimorphism and cannabalism in tadpoles of Scaphiopus bombifrons (Amphibia, Salientia). Southwestern Naturalist 1: 105-108.
    • Bragg, A.N. 1962a. Predation on arthropods by spadefoot tadpoles. Herpetologica 18: 144.
    • Bragg, A.N. 1962b. Predator-prey relationship in two species of spadefoot tadpoles with notes on some features of their behavior. Wasmann Journal of Biology 20: 81-97.
    • Bragg, A.N. 1965. Gnomes of the Night: The Spadefoot toads. University of Pennsylvania Press, Philadelphia.
    • Bragg, A.N. 1966. Longevity of the tadpole stage in the plains spadefoot (Amphibia: Salientia). Wasmann Journal of Biology 24: 71-73.
    • Bragg, A.N. and O. King. 1960. Aggregational and associated behavior in tadpoles of the Plains spadefoot. Wasmann Journal of Biology 18:273-289.
    • Bragg, A.N. and W.N. Bragg. 1958. Parasitism of Spadefoot tadpoles by Saprolegnia. Herpetologica 14: 34.
    • Bragg, A.N. and W.N. Bragg. 1958b. Variations in the mouth parts in tadpoles of Scaphiopus (Spea) bombifrons Cope (Amphibia: Salientia). Southwestern Naturalist 3: 55-69.
    • Bragg. A.N. 1945. The spadefoot toads in Oklahoma with a summary of our knowledge of the group. II. American Naturalist 79: 52-72.
    • Brown, H.A. 1976. The status of California and Arizona populations of the western spadefoot toads (Genus Scaphiopus). Contributions of Science of the Natural History Museum of Los Angeles Co. 286 pp.
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    • Buchholz, D. and T.B. Hayes. 2000. Evolution of diversity in anuran tadpoles: accelerated metamorphosis in spadefoot toads. American Zoologist 40(6):957.
    • Buchholz, D.R. and T.B. Hayes. 2002. Evolutionary patterns of diversity in spadefoot toad metamorphosis (Anura: Pelobatidae). Copeia 1:180-189.
    • Bureau of Indian Affairs, Department of the Interior. 1981. Draft Environmental Impact Statement. Unpublished report for the Crow/Shell Coal Lease, Crow Indian Reservation, Montana.
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