Plains Spadefoot - Spea bombifrons
(see State Rank Reason below)
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
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
ScoreE - Relatively Stable (±25% change)
CommentAs the species uses pasture and some agricultural lands, habitat has likely been relatively stable since European arrival
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).
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
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
3.5 + 0 (geographic distribution) + 0 (environmental specificity) + 0 (short-term trend) + 0 (threats) = 3.5
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).
JUVENILES AND ADULTS
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).
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.
Western Hemisphere Range
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:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(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:
- 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);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- 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: mtnhp.org/requests
) 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.
- 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.
- Commonly Associated with these Ecological Systems
Forest and Woodland Systems
Recently Disturbed or Modified
Shrubland, Steppe and Savanna Systems
Sparse and Barren Systems
Wetland and Riparian Systems
- Occasionally Associated with these Ecological Systems
Forest and Woodland Systems
Human Land Use
Recently Disturbed or Modified
Shrubland, Steppe and Savanna Systems
Wetland and Riparian Systems
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).
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?
- [PRESI] Powder River Eagle Studies Incorporated. 1998a. Big Sky Mine 1997 wildlife monitoring studies. Powder River Eagle Studies Incorporated. Gillete, WY.
- [PRESI] Powder River Eagle Studies Incorporated. 1998b. Spring Creek Mine 1997 wildlife monitoring studies. Powder River Eagle Studies Incorporated. Gillete, WY.
- [VTNWI] VTN Wyoming Incorporated. No Date. Second year's analysis of terrestrial wildlife on proposed mine access and railroad routes in southern Montana and northern Wyoming, March 1979 - February 1980. VTN Wyoming Incorporated. Sheridan, WY. 62 p.
- [WESTECH] Western Technology and Engineering Incorporated. 1998. Wildlife Monitoring Absaloka Mine Area 1997. Western Technology and Engineering, Inc., Helena, Mt.
- 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.
- Brunson, R.B. 1955. Check list of the amphibians and reptiles of Montana. Proceedings of the Montana Academy of Sciences 15: 27-29.
- Buchholz, D. and T.B. Hayes. 1996. Comparative larval biology in spadefoot toads. American Zoologist 36(5):97.
- 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.
- Burton, S.R., D.A. Patla, and C.R. Peterson. 2002. Amphibians of Red Rock Lakes National Wildlife Refuge: occurrence, distribution, relative abundance, and habitat associations. Herpetology Laboratory, Department of Biological Sciences, Idaho State University, Pocatello, ID. 66 p.
- Cannatella, D.C. 1985. A phylogeny of primitive frogs (Archaeobatrachians). Ph.D. Thesis, University of Kansas, Lawrence, Kansas.
- Carlson, J. (Coordinator, Montana Animal Species of Concern Committee). 2003. Montana Animal Species of Concern January 2003. Helena, MT: Montana Natural Heritage Program and Montana Fish, Wildlife, and Parks. In Press. 12p.
- Chrapliwy, P.S. and J.S. Findley. 1956. Records of the central plains spadefoot toad, Scaphiopus bombifrons Cope, in South Dakota and Wyoming. Herpetologica 12: 124.
- Cook, F.R. 1960. New localities for the plains spadefoot toad, tiger salamander, and the great plains toad in the Canadian prairies. Copeia 1960 (4): 363-364.
- Cooper, S.V., C. Jean, and P. Hendricks. 2001. Biological survey of a prairie landscape in Montana's glaciated plains. Report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, MT. 24 pp. plus appendices.
- Cope, E.D. 1863. On Trachycephalus, Scaphiopus, and other American Batrachia. Proceedings of the Academy of National Sciences, Philadelphia. Volume 15, p. 53.
- Cope, E.D. 1872. Report on the recent reptiles and fishes of the survey, collected by Campbell Carrington and C.M. Dawes. pp. 467-469 In: F.V. Hayden, Preliminary report of the United States geological survey of Montana and portions of adjacent territories; being a fifth annual report of progress. 538 pp. 42nd Congress, 2nd Session, House Executive Document Number 326. Serial 1520.
- Cope, E.D. 1875. Check-list of North American Batrachia and Reptilia; with a systematic list of the higher groups, and an essay on geographical distribution. Based on the specimens contained in the U.S. National Museum. U.S. Natioanl Museum Bulletin 1: 1-104.
- Cope, E.D. 1889. The Batrachia of North America. Bulletin of the U.S. National Museum 34: 1-525, figs. 1-119, pls. 1-86.
- Corn, P.S., E. Muths, and W.M. Iko. 2000. A comparison in Colorado of three methods to monitor breeding amphibians. Northwestern Naturalist 81:22-30.
- Crother, B.I. (ed.) 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico. SSAR Herpetological Circular No. 37:1-84.
- Dimmitt, M.A. and R. Ruibal. 1980. Exploitation of food resources by spadefoot toads (Scaphiopus). Copeia (4): 854-862.
- Econ, Inc. 1988. Wildlife monitoring report, 1987 field season, Big Sky Mine. March 1988. In Peabody Mining and Reclamation Plan Big Sky Mine Area B. Vol. 8, cont., Tab 10 - Wildlife Resources. Appendix 10-1, 1987 Annual Wildlife Report.
- Farrar, E.S. and J.D. Hey. 1997. Carnivorous spadefoot (Spea bombifrons Cope) tadpoles and fairy shrimp in Western Iowa. Journal of the Iowa Academy of Science 104(1): 4-7.
- Feigley, H. P. 1997. Colonial nesting bird survey on the Bureau of Land Management Lewistown District: 1996. Unpublished report, U.S. Bureau of Land Management, Lewistown, Montana.
- Firschen, I.L. 1950. A new record of Spea bombifrons from northern Mexico and remarks on the status of the hammondii group of spadefoot group of spadefoot anurans. Herpetologica 6(3): 75-77.
- Fjell, Alan K., 1986, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1985 field season. March 1986.
- Fjell, Alan K., and Brian R. Mahan, compilers., 1984, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1983 field season. February 1984.
- Fjell, Alan K., and Brian R. Mahan., 1983, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1982 field season. May 1983.
- Fjell, Alan K., and Brian R. Mahan., 1985, Peabody Coal Company Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1984 field season. February 1985.
- Fjell, Alan K., and Brian R. Mahan., 1987, Big Sky Mine, Rosebud County, MT. Wildlife monitoring report: 1986 field season. April 1987.
- Forester, D.C. 1969. Reproductive isolation and hybridization between the spadefoot toads (Scaphiopus bombifrons) and (Scaphiopus hammondii) in west Texas. Unpublished M.S. Thesis, Texas Tech University, Lubbock, Texas.
- Forester, D.C. 1973. Mating call as a reproductive isolating mechanism between Scaphiopus bombifrons and Scaphiopus hammondii. Copeia 1973(1): 60-67.
- Forester, D.C. 1975. Laboratory evidence for potential gene flow between two species of spadefoot toads Scaphiopus bombifrons and Scaphiopus hammondii. Herpetologica 31(3): 282-286.
- Gates, M.T. 2005. Amphibian and reptile baseline survey: CX field study area Bighorn County, Montana. Report to Billings and Miles City Field Offices of Bureau of Land Management. Maxim Technologies, Billings, MT. 28pp + Appendices.
- Gilmore, R.J. 1924. Notes on the life history and feeding habits of the spadefoot toad of the western plains. Colorado College Publications in Science 13(1): 1-12.
- Gilmore, R.J. 1929. Life history and feeding habits of the spadefoot toad. Journal of the Colorado-Wyoming Academy of Science 1(1): 41.
- Goldberg, S.R. and C.R. Bursey. 2002. Helminths of the plains spadefoot, Spea bombifrons, the western spadefoot, Spea hammondii, and the Great Basin spadefoot, Spea intermontana (Pelobatidae). Western North American Naturalist 62(4):491-495.
- Hanauska-Brown, L., B.A. Maxell, A. Petersen, and S. Story. 2014. Diversity Monitoring in Montana 2008-2010 Final Report. Montana Fish, Wildlife & Parks. Helena, MT. 78 pp.
- Hendricks, P. and J.D. Reichel. 1996b. Preliminary amphibian and reptile survey of the Ashland District, Custer National Forest: 1995. Montana Natural Heritage Program, Helena, MT. 79 p.
- Hendricks, P. and J.D. Reichel. 1998. Amphibian and reptile survey on Montana refuges: 1996. Montana Natural Heritage Program, Helena, MT. 19 p.
- Hendricks, P., S. Lenard, D.M. Stagliano, and B.A. Maxell. 2013. Baseline nongame wildlife surveys on the Fort Peck Indian Reservation. Report to the Assiniboine and Sioux Tribes of the Fort Peck Indian Reservation. Montana Natural Heritage Program, Helena, MT. 83 p.
- Holycross, A.T. and K.B. Malmos. 1992b. Spea bombifrons (Plains spadefoot). Herpetological Review 23(1): 25.
- Hossack, B. and P.S. Corn. 2001. Amphibian survey of Medicine Lake National Wildlife Refuge Complex: 2001. USGS Northern Rocky Mountain Science Center, Aldo Leopold Wilderness Research Institute, Missoula, MT. 13 p.
- Hughes, N. 1965. Comparison of frontoparietal bones of Scaphiopus bombifrons and Scaphiopus hammondii as evidence for interspecific hybridization. Herpetologica 21: 196-201.
- Johnson, K.H., G.L. Kurtz, R.A. Olson and T.D. Whitson. 1994. Spea bombifrons (Plains Spadefoot) Herpetological Review 25(2): 75.
- Joslin, Gayle, and Heidi B. Youmans. 1999. Effects of recreation on Rocky Mountain wildlife: a review for Montana. [Montana]: Montana Chapter of the Wildlife Society.
- Justus, J.T., M. Sandomir, T. Urquhart and B.O. Ewan. 1977. Developmental rates of two species of toads from the desert southwest. Copeia 1977(3): 592-594.
- Klassen, M.A. 1990. Spadefoot spring. Nature Canada 19: 8-9.
- Kluge, A. G. 1966. A new pelobatine frog from the lower Miocene of South Dakota with a discussion of the evolution of the Scaphiopus-Spea complex. Contributions of Science to the Natural History Museum of Los Angeles County 113: 1-26.
- Landreth, H.F. and M.T. Christensen. 1971. Orientation of the Plains spadefoot toad, Scaphiopus bombifrons, to solar cues. Herpetologica: 27(4): 454-461.
- Lewin, V. 1963. The herpetofauna of southeastern Alberta. Can. Field-Nat. 77:203-214.
- Lomolino, M.V. and G.A. Smith. 2004. Terrestrial vertebrate communities at black-tailed prairie dog (Cynomys ludovicianus) towns. Biological Conservation 115(1):89-100.
- Lynch, C. 2001. North American Amphibian Monitoring Program's Montana frog-call survey: report on year two of a program in south-central Montana started April 2001 and completed in June 2001. Zoo Montana Conservation Through Education Program, Billings MT. 12 p.
- Matthews, W.L. 1979. Wibaux-Beach wildlife baseline study - nongame species. Bureau of Land Management, Miles City, MT. 93 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 USFS Region 1, Order Number 43-0343-0-0224. University of Montana, Wildlife Biology Program. Missoula, MT. 161 p.
- McAllister, C.T., C.R. Bursey, and D.B. Conn. 2005. Endoparasites of Hunter's spadefoot, Scaphiopus hurterii and plains spadefoot, Spea bombifrons (Anura: Scaphiododidae), from southern Oklahoma. Texas Journal of Science 57(4):383-389.
- McEneaney, T. and J. Jensen. 1974. The reptiles and amphibians of the Charles M. Russell National Wildlife Range - 1974. Charles M. Russell National Wildlife Refuge. Lewistown, MT. 3 p.
- Moore, J.E. 1952. The spadefoot toad, Scaphiopus, in Alberta. Copeia 1952: 278.
- Morlan, R.E. and J.V. Matthews, Jr. 1992. Range extension for the plains spadefoot, Scaphiopus bombifrons, inferred from owl pellets found near outlook, Saskatchewan. Canadian Field Naturalist 106(3): 311-315.
- Nero, R.W. 1959. The Spadefoot toad in Saskatchewan. Blue Jay 17(1): 41-42.
- Oechsli, L.M. 2000. Ex-urban development in the Rocky Mountain West: consequences for native vegetation, wildlife diversity, and land-use planning in Big Sky, Montana. M.Sc. Thesis. Montana State University, Bozeman. 73 p.
- Ott, J.A. and D.E. Scott. 1999. Effects of toe-clipping and PIT-tagging on growth and survival in metamorphic Ambystoma opacum. Journal of Herpetology 33(2): 344-348.
- Peterson, C.R., C.J. Askey, and D.A. Patla. 1993. Amphibians and reptiles along the Grand Loop and Fountain Freight Roads between Madison Junction and Biscuit Basin in Yellowstone National Park. 26 July, 1993. Greater Yellowstone Ecosystem Amphibian Survey and Monitoring Program, Herpetology Laboratory, Department of Biological Sciences, Idaho State University, Pocatello, ID. 45 p.
- Pfening, K.S. 2003. A test of alternative hypotheses for the evolution of reproductive isolation between spadefoot toads: support for the reinforcement hypothesis. Evolution 57(12):2842-2851.
- Pfennig, K.S. and M.A. Simovich. 2002. Differential selection to avoid hybridization in two toad species. Evolution 56(9): 1840-1848.
- Pfenning, D.W. 1992. Proximate and functional causes of polyphenism in an anuran tadpole. Functional Ecology 6:167-174.
- Pfenning, D.W., H.K. Reeve and P.W. Sherman. 1993. Kin recognition and cannibalism in spadefoot toad tadpoles. Animal Behaviour 46(1): 87-94.
- Pierce, J.R. 1976. Distribution of two mating call types of the plains spadefoot (Scaphiopus bombifrons) in southwestern United States. Southwest Naturalist: 20(4): 578-582.
- Pilliod, D.S. and T.C. Esque. 2023. Amphibians and reptiles. pp. 861-895. In: L.B. McNew, D.K. Dahlgren, and J.L. Beck (eds). Rangeland wildlife ecology and conservation. Cham, Switzerland: Springer. 1023 p.
- Plummer, M.V. and G. Turnipseed. 1982. Scaphiopus bombifrons (Plains spadefoot). Herpetological Review 13(3): 80.
- Plumpton, D.L. and R.S. Lutz. 1993. Prey selection and food habits of burrowing owls in Colorado. Great Basin Naturalist 53: 299-304.
- Potthoff, T.L. and J.D. Lynch. 1986. Interpopulation variability in mouthparts in Scaphiopus bombifrons in Nebraska (USA) (Amphibia: Pelobatidae). Prairie Naturalist 18(1): 15-22.
- Powder River Eagle Studies, Inc., Gillette, WY., 1999, Spring Creek Mine 1998 Wildlife Monitoring. March 1999.
- Powder River Eagle Studies, Inc., Gillette, WY., 2000, Spring Creek Mine 1999 Wildlife Monitoring. March 2000.
- Powder River Eagle Studies, Inc., Gillette, WY., 2000, Spring Creek Mine 2000 Wildlife Monitoring. March 2000.
- Preston, W.B. and D.R.M. Hatch. 1986. The Plains spadefoot (Scaphiopus bombifrons) in Manitoba (Canada). Canadian Field Naturalist 100(1): 123-125.
- Rauscher, R.L. 1998. Amphibian and reptile survey on selected Montana Bureau of Reclamation impoundments. Montana Department of Fish, Wildlife and Parks, Nongame Program. Bozeman, MT. 24 pp.
- Reichel, J. and D. Flath. 1995. Identification of Montana's amphibians and reptiles. Montana Outdoors 26(3):15-34.
- Reichel, J.D. 1996. Preliminary amphibian and reptile survey of the Helena National Forest: 1995. Montana Natural Heritage Program. Helena, MT. 87 pp.
- Reichel, J.D. 1997. Amphibian and reptile survey in northcentral Montana on the Lewistown District, BLM. Unpublished report.
- Reichel, J.D. 1997a. Amphibian, reptile and northern bog lemming survey on the Rocky Mountain Front: 1996. Montana Natural Heritage Program, Helena, MT. 81 p.
- Roedel, M.D. and P. Hendricks. 1998a. Amphibian and reptile survey on the Bureau of Land Management Lewistown District: 1995-1998. Montana Natural Heritage Program, Helena, MT. 53 p.
- Roedel, M.D. and P. Hendricks. 1998b. Amphibian and reptile inventory on the Headwaters and Dillon Resource Areas in conjunction with Red Rocks Lakes National Wildlife Refuge: 1996-1998. Montana Natural Heritage Program, Helena, MT. 46 p.
- Sadler, L.M. and M.A. Elgar. 1994. Cannibalism among amphibian larvae: A case of good taste. Trends in Ecology and Evolution 9(1): 5-6.
- Sattler, P.W. 1978. Biochemical genetic investigations of introgressive hybridization and systematic relationships in the spadefoot toads, genus Scaphiopus. Ph.D. Dissertation, Texas Technical University.
- Sattler, P.W. 1985. Introgressive hybridization between the spadefoot toads Scaphiopus bombifrons and Scaphiopus multiplicatus (Salientia: Pelobatidae). Copeia 1985(2): 324-332.
- Sexton, O.J. and K.R. Marion. 1974. Probable predation by Swainson’s hawks on swimming spadefoot toads. Wilson Bulletin 86(2): 167-168.
- Shannon, F.A. 1953. Scaphiopus bombifrons, a state record for Arizonia. Herpetologica 9: 127-128.
- Simovich, M.A. 1985. Analysis of a hybrid zone between the spadefoot toads (Scaphiopus multiplicatus) and (Scaphiopus bombifrons). Ph.D. diss., University of California, Riverside, CA.
- Simovich, M.A. 1994. The dynamics of a spadefoot toad (Spea multiplicata and S. bombifrons) hybridization system. Pp. 167-182 in P.R. Brown and J.W. Wright, eds. Herpetology of North American deserts, special publication no. 5. Southwestern Herpetolo
- Simovich, M.A. and C.A. Sassaman. 1986. Four independent electrophoretic markers in spadefoot toads. Journal of Heredity 77(6): 410-414.
- Simovich, M.A., C.A. Sassamam, and A. Chovnick. 1991. Post-mating selection of hybrid toads (Scaphiopus multiplicatus and Scaphiopus bombifrons). Proceedings of the San Diego Society of Natural History 1991: 1-6.
- Smith, H.M., C.E. Bock and J.H. Bock. 1993b. Spea bombifrons (Plains spadefoot). Herpetological Review 24(4): 154.
- Stebbins, R.C. 1985. A field guide to western reptiles and amphibians. Houghton Mifflin Company, Boston. 336 pp.
- Sullivan, B.K. 1985. Sexual selection and mating system variation in anuran amphibians of the Arizona-Sonoran desert. Great Basin Naturalist 45(4): 688-696.
- Sullivan, B.K. and E.A. Sullivan. 1985. Variation in advertisement calls and male mating success of Scaphiopus bombifrons, Scaphiopus couchi and Scaphiopus multiplicatus (Pelobatidae). Southwestern Naturalist 30(3): 349-356.
- Swanson, D.L. and B.M. Graves. 1995. Supercooling and freeze intolerance in overwintering juvenile spadefoot toads (Scaphiopus bombifrons). Journal of Herpetology 29(2): 280-285.
- Tanner, V.M. 1939. A study of the genus Scaphiopus. The spade-foot toads. Great Basin Naturalist 1: 3-23.
- Tanner, W.W. 1989b. Status of Spea stagnalis Cope (1875), Spea intermontanus Cope (1889), and a systematic review of Spea hammondii Baird (1839) (Amphibia: Anura). Great Basin Naturalist 49(4): 503-510.
- Timken, R. No Date. Amphibians and reptiles of the Beaverhead National Forest. Western Montana College, Dillon, MT. 16 p.
- Trauth, S.E., B.P. Butterfield, and W.E. Meshaka, Jr. 1989. Scaphiopus bombifrons (plains spadefoot). Herpetological Review 20(1): 12.
- Trowbridge, A.H. and M.S. Trowbridge. 1937. Notes on the clevage rate of Scaphiopus bombifrons Cope, with additional remarks on certain aspects of its life history. American Naturalist 71(736): 460-480.
- Trowbridge, M. 1941. Studies on the normal development of Scaphiopus bombifrons Cope. I. The clevage period. Transactions of the American Microscopical Society 60: 508-526.
- Trowbridge, M. 1942. Studies on the normal development of Scaphiopus bombifrons Cope. II. The later embryonic and larval periods. Transactions of the American Microsopical Society 61: 66-83.
- Turner, F.B. 1951. A checklist of the reptiles and amphibians of Yellowstone National Park with incidental notes. Yellowstone Nature Notes 25(3): 25-29.
- Turner, F.B. 1955. Reptiles and amphibians of Yellowstone National Park. Yellowstone Interpretive Series No. 5. Yellowstone Library and Museum Association. Yellowstone National Park, WY. 40 p.
- Van Kirk, R., L. Benjamin, and D. Patla. 2000. Riparian area assessment and amphibian status in the watersheds of the Greater Yellowstone Ecosystem. Greater Yellowstone Coalition, Bozeman, MT. 102 p.
- Vitt, L.J., J.P. Caldwell, and D.B. Shepard. 2005. Inventory of amphibians and reptiles in the Billings Field Office Region, Montana. Sam Noble Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, OK. 33 pp.
- Voss, W.J. 1961. Rate of larval development and metamorphosis of the spadefoot toad, Scaphiopus bombifrons. Southwestern Naturalist 6: 168-174.
- VTN Colorado, Inc. Decker Coal Company., 1975, Draft environmental impact assessment for the proposed North Extension of the West Decker Mine.
- Werner, J.K., B.A. Maxell, P. Hendricks and D.L. Flath. 2004. Amphibians and Reptiles of Montana. Mountain Press Publishing Company: Missoula, MT. 262 pp.
- Wheeler, G.C. and J. Wheeler. 1966. The amphibians and reptiles of North Dakota. University of North Dakota, Grand Forks, ND. 104 pp.
- Wiens, J.J. 1989. Ontogeny of the skeleton of Spea bombifrons (Anura: Pelobatidae). Journal of Morphology 202(1): 29-52.
- Woodward, B.D. 1982. Sexual selection and nonrandom mating patterns in desert anurans (Bufo woodhousei, Scaphiopus couchi, S. multiplicatus, and S. bombifrons). Copeia 1982(2): 351-355. 28.
- Woody, J.R. 1967. Study of certain meteorological influences on the emergence and breeding with notes on the embryology of the plains spadefoot toad, Scaphiopus bombifrons. M.A. Thesis, University of Northern Colorado, Greely, 72 pp.
- Woody, J.R. and B.O. Thomas. 1966. Preliminary studies of the Scaphiopus bombifrons in northeastern Colorado. Journal of the Colorado-Wyoming Academy of Science 5(7): 11-12.
- Woody, J.R. and B.O. Thomas. 1968. Study of certain meterological influences on the emergence and breeding of the plains spadefoot toad, Scaphiopus bombifrons. Journal of the Colorado-Wyoming Academy of Science 6(1): 11.
- Yarrow, H.C. 1882. Check list of North American reptilia and batrachia, with catalogue of specimens in the U.S. National Museum. United States National Museum Bulletin 24. 249 p.
- Zweifel, R.G. 1968b. Reproductive biology of anurans of the arid southwest, with emphasis on adaptation of embryos to temperature. Bulletin of the American Museum of Natural History 140(1): 1-64.
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