Snapping Turtle - Chelydra serpentina
State Rank Reason (see State Rank above)
Little is known about native populations of this species in Montana, which makes assessment of threats and trends difficult. This species has a high age of maturity and low recruitment, making populations vulnerable to extirpation.
- Details on Status Ranking and Review
Snapping Turtle (Chelydra serpentina) Conservation Status Review
Review Date = 09/27/2018
ScoreF - 20,000-200,000 km squared (about 8,000-80,000 square miles)
Comment73,215 square Kilometers from Natural Heritage Program range maps
ScoreE - Relatively Stable (±25% change)
CommentHabitat is likely stable within +/- 25% since European settlement, stock ponds may have increased the amount of habitat for this species
ScoreU - Unknown. Short-term trend in population, range, area occupied, and number and condition of occurrences unknown.
CommentNo data on trends available
ScoreU - Unknown. The available information is not sufficient to assign degree of threat as above. (Severity, scope, and immediacy are all unknown, or mostly [two of three] unknown or not assessed [null].)
CommentUnknown. Unrestricted harvest of the species has been implicated in local declines elsewhere in the species range. As Montana is at the northern periphery of this species range, unusually cold winters or adverse weather events may effect recruitment.
ScoreA - Highly Vulnerable. Species is slow to mature, reproduces infrequently, and/or has low fecundity such that populations are very slow (> 20 years or 5 generations) to recover from decreases in abundance; or species has low dispersal capability such that extirpated populations are unlikely to become reestablished through natural recolonization (unaided by humans).
CommentSpecies has a very high age of maturity, and although a moderate number of eggs are produced relatively few young make it through their first winter.
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.
CommentFound in lotic and lentic waterbodies associated with the Yellowstone and Missouri river drainages
Raw Conservation Status Score
3.5 + 0 (geographic distribution) + 0 (environmental specificity) + 0 (long-term trend) + -0.5 (intrinsic vulnerability) = 3
Eggs are white and round. They range from 23-33 mm (0.91-1.3 in) in length, averaging 27-28 mm (1.06-1.1 in). The shell is leathery and is somewhat pliable. Clutch size ranges from 6-109 eggs (Werner et al. 2004).
Hatchings are dark brown to black with conspicuous ridges on their carapace. The carapace
measure 2.5-3.8 cm (1-1.5 inches) in length (Ernst et al. 1994, Werner et al. 2004).
JUVENILES AND ADULTS:
This species are large, stout turtles with an adult carapace length (CL) typically 20-35 cm (8-14 in), but grow larger in populations of the southern United States (Degenhardt et al. 1996). Adults usually weigh 4.5-16 kilograms (10-35 lbs). However, one Montana individual found in the Redwater River reached 32 lbs (14.5 kg) (Aderhold 1980) and another Montana specimen reportedly reached 48 lbs (21.8 kg) (Werner et al. 2004). Their tails are long about the length of the carapace (dorsal shell), with three rows of distinct sawtooth-shaped projections. The plastron (ventral shell) is brown with three keels that are more easily discerned in younger individuals. In older individuals, a good portion of the carapace is usually covered with algae. The cream-yellow plastron is greatly reduced compared to other turtles, and forms a cross-like shape. It has a large head with slightly hooked upper jaw. They have long necks with tubercles on the dorsal surface. They have webbed toes and powerful claws. The anal vent of the male usually extends past the posterior edge of the carapace, whereas it is found anterior to the rim in females. Males will usually grow larger than females (Hammerson 1999).
The Snapping Turtle is the only turtle in Montana with a reduced plastron covering less than half of the ventral surface, keeled scutes on the carapace, and a tail approximately as long as the carapace. There is no bright orange or yellow coloration as found on the Painted Turtle (Chrysemys picta
), and their carapace is hard, unlike the soft, leathery shell of the Spiny Softshell (Apalone spinifera
) (Black 1970c, Black and Black 1971, Werner et al. 2004).
Western Hemisphere Range
The Snapping Turtle (Chelydra serpentina) ranges along the Atlantic Coast from Nova Scotia, Canada to Florida and westerly to the Rocky Mountain front, from southeastern Manitoba, Canada to Texas, and Mexico (Ernst et al. 1994). Two subspecies are recognized: the Florida Snapping Turtle (C. serpentina osceola) and the subspecies inhabiting Montana, the Eastern Snapping Turtle (C. serpentina serpentina) (Crother 2008).
In Montana, native populations are found from Carter County, west to Carbon and Stillwater Counties, and northeasterly to Phillips County (MTNHP 2022). Most records are from the southeastern portion of the state in the Yellowstone River system and tributaries, especially along the Tongue River drainage. Currently, there are no confirmed Montana records from the Missouri River or its tributaries above the dam on Fort Peck Lake. Introduced animals have been detected in several counties in western Montana and control efforts are ongoing (Maxell et al. 2003, MTNHP 2022). Detections in these areas should be reported to Montana Fish, Wildlife, and Parks.
Maximum elevation: 1,403 m (4603 ft) in Gallatin County (Scott Barndt; MTNHP 2022).
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 specific migratory information for Montana is currently available.
Research from other locations indicates that the Snapping Turtle may migrate up to several miles between the water bodies and nesting areas. Evidence suggests that adults may use the sun as a navigational guide during overland migrations (Ernst et al. 1994). Some may travel a few kilometers between summer range and winter hibernation sites, while others overwinter within their summer range (Brown and Brooks 1994). In Ontario, the distances traveled to nesting sites ranged from 370 to 2020 m (1,214 to 6,627 ft) and a mean of 1,053 m (3,455 ft), and movements were greatest from spring to mid-July (Pettit et al. 1995). Distances traveled by C. serpentina in South Dakota ranged from 0 to 6.05 km (3.76 mi) but averaged just 1.1 km (0.68 mi) (Hammer 1969).
Habitats used in Montana are probably similar to other areas in their range, but local studies are lacking and there is little qualitative information available. They have been captured or observed in backwaters along major rivers, at smaller reservoirs, and in smaller streams and creeks with permanent flowing water and sandy or muddy bottoms (Reichel 1995b, Hendricks and Reichel 1996b, Gates 2005, Paul Hendricks, personal observation). They have also been observed in temporary pools along small intermittent streams near Decker, Montana (M. Gates, personal observation). Nesting habitat and nest sites have not been described.
Freshwater habitats with a soft mud bottom and cover such as abundant aquatic vegetation or submerged brush and logs are preferred (Hammerson 1999) and brackish water in some areas. Although found most often in shallower water, an Ontario, Canada individual was observed by R. J. Brooks regularly diving 10 m (33 ft) to the bottom of a lake (Ernst et al. 1994). Temporary ponds and reservoirs may also be occupied. Hatchlings and juveniles tend to occupy shallower sites than mature individuals in the same water bodies. They are mostly bottom dwellers, where they spend much of their time. Although highly aquatic, they may make long movements overland if their pond or marsh dries (Baxter and Stone 1985, Ernest et al. 1994, Hammerson 1999). Snapping Turtles have a high-water loss gradient (0.64 g/hour or 0.02 oz/hour); therefore, they are at risk out of water in warm or dry conditions and rarely bask out of water. Aerial basking is more common in cooler environments in the northern portions of their range (Ernst et al. 1994) and has been observed on the Tongue River of southeastern Montana (Matt Gates, personal observation). They hibernate singly or in groups in streams, lakes, ponds, or marshes; in bottom mud, in or under submerged logs or debris, under an overhanging bank, or in Muskrat (Ondatra zibethicus
spp.) tunnels; often in shallow water; sometimes in anoxic sites (Brown and Brooks 1994).
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
Wetland and Riparian Systems
- Occasionally Associated with these Ecological Systems
Recently Disturbed or Modified
Wetland and Riparian Systems
The diets of Snapping Turtle have not been studied in Montana, but they are known to eat about anything that can be captured while foraging in the water. They eat many kinds of vertebrates (fish, amphibians, reptiles, aquatic birds, and small mammals), invertebrates (insects, spiders, crustaceans, mollusks, leeches, and sponges), various plants and algae, and carrion (Pell 1940, Ernst et al. 1994). Their diet appears to be dependent on availability. In New York and Massachusetts, specimens collected from marshy lakes consumed 90% plant material, but individuals from small streams consumed 100% crayfish (Pell 1940). The young often search actively for food, but adults generally lie in ambush to seize their prey (Ernst et al. 1994). This species is known to eat nine orders of insects (ants, beetles, and moths the most abundant), and spiders, scorpions, ticks, and mites have been reported in the diet (Hammerson 1999).
Snapping Turtles are known to hibernate independently or in groups. They overwinter in lakes, ponds, streams, or marshes; in bottom mud, in or under submerged logs or debris, under overhanging banks, in muskrat tunnels, or in the saturated soil of pastures (Meeks and Ultsch 1990). They sometimes overwinter in shallow, anoxic water but survivorship is higher in normoxic condition. Underwater winter movements are not uncommon. In Ontario, C. serpentina
emerged from winter dormancy when water reached about 7.5 °C (45.5 °F) (Obbard and Brooks 1981b, Meeks and Ultsch 1990, Brown and Brooks 1994).
Populations can vary greatly regionally, locally, and temporally (Froese and Burghardt 1975); therefore, population data from other locations cannot be extrapolated to Montana with any accuracy. In Ontario, males occupied relatively stable, overlapping home ranges; with summer ranges between 0.4 to 2.3 hectares (Galbraith et al. 1987). Also in Ontario, the foraging home ranges documented for a year at three sites during July to August were 2.3 to 18.1 hectares (means fell between 5 and 9 hectares). The home range length was about 550 to 1,990 m (1,804 to 6,529 ft); however, home range size did not vary with habitat productivity (Brown et al. 1994). In another Ontario study, home range size over a year was 1.0 to 28.4 hectares, averaging about 9 hectares for females and about 2 to 3 hectares for males (Pettit et al. 1995). Densities in marshes of South Dakota reached one per 2 acres (Hammer 1969).
Egg survival is usually low, not more than 0.22, and adult survival generally high, over 0.90. A population in Ontario, was characterized as stable, with adult female annual survivorship greater than 0.95. Later, a great increase in adult mortality occurred, apparently due primarily to Northern River Otter (Lontra canadensis
) predation on hibernating turtles, resulting in no compensatory density-dependent response in reproduction and recruitment (Brooks et al. 1991, Iverson 1991). In Michigan, actual annual survivorship of juveniles was over 0.65 by age 2 and averaged 0.77 between ages 2 and 12 years. Annual survivorship of adult females ranged from 0.88 to 0.97. Population stability was most sensitive to changes in adult or juvenile survival and less sensitive to changes in age at sexual maturity, nest survival, or fecundity (Congdon et al. 1994). In South Dakota, Hammer (1969) reported that predators destroyed 59% of nests, and that emergence in undisturbed nests was less than 20%. Snapping Turtles may have limited range in the north because of overwintering mortality (Obbard and Brooks 1981b). Snapping Turtles are relatively long-lived. In an Ontario population, females have an average lifespan of 40 years (Galbraith and Brooks 1989), and average lifespan of a South Carolina population was 28 years (Ernst et al 1994). The record for a captive individual is 47 years (Werner et al. 2004).
Snapping Turtles frequently incur high rates of nest predation by various animals, particularly skunks, Raccoon (Procyon lotor
), foxes, American Black Bear (Ursus americanus
), American Crow (Corvus brachyrhynchos
), and snakes (Congdon et al. 1987, Ernst et al. 1994, Hammerson 1999). In Michigan, eggs and young typically incur 60-100% predation, primarily by Raccoons (Harding 1997). Temple (1987) suggest that nest predation increases near habitat edges. Raccoons, Coyote (Canis latrans
), Northern River Otter, American Black Bear, and often humans will prey on adults. Herons, bitterns, hawks, eagles, various predatory fish, and American Bullfrog (Lithobates catesbeianus
) prey on hatchlings and juveniles (Ernst et al. 1994). Compared with other species, C. serpentina
, uses very aggressive display postures to thwart potential predators, such as facing its attacker and lifting its legs in various positions while gaping its mouth. (Dodd et al. 1975). Snapping Turtles are often parasitized by leaches (Placobdella
spp.) and a protozoan blood parasite (Haemogregarina balli
). An Ontario individual reportedly had 768 leaches attached (Brooks et al. 1990). Despite high rates of infestation, Brown and Brooks (1994) found that these parasites do not negatively affect reproductive output. Humans are the only recorded predators in Montana (Paul Hendricks, personal observation).
In Iowa, males can reach sexual maturity by their fifth year and females as early as their seventh (Christiansen and Burken 1979). However, in some populations, maturity is not reached before 15 years. The youngest mature female known from Michigan was 12 years. In Ontario the average age of first nesting ranged from 17-19 years. Virtually no reproductive data exists specific to Montana. However, Montana populations likely exhibit traits similar to those elsewhere. Warming temperatures trigger nesting behavior in females. Obbard and Brooks (1987) developed a model to predict the onset of nesting activity from temperature data in Ontario. Females may travel several kilometers to locate a suitable nest site. Obbard and Brooks (1980) reported a round trip distance of 16 km (9.94 mi) to a nest site and back (Ernst et al. 1994).
Nests are usually built in open areas a hundred meters or more from water; excavated in soft sand, loam, vegetation debris, sawdust piles, and Beaver (Castor canadensis
) and Muskrat lodges. Females generally dig nests from 7-18 cm (2.76-7.09 in) (Congdon et al. 1987, Ernst et al. 1994, Hammerson 1999). In northern regions, eggs are generally deposited in late May to early June. Recorded clutch sizes range from 6 to 104, but typically 20-40 eggs are laid. Clutch size tends to increase from southerly to northerly latitudes. Eggs incubate for 55-125 days (usually 75-95) before hatching, with incubation period increasing with latitude. The sex of each hatchling is determined by each egg’s temperature during a critical developmental period, known as temperature dependent sex determination. Relatively cooler temperatures produce females and warmer temperatures produce males. The sex ratio of hatchlings is commonly 1:1 (Ernst et al. 1994). Nest site selection is critical for survival of hatchlings. Eggs buried in moister substrate generally support better embryonic development and larger hatchlings, compared to eggs in drier environments (Morris et al. 1983). The incubation environment of eggs can later effect growth and viability of young Snapping Turtles (McKnight and Gutzke (1993). Bobyn and Brooks (1994) suggest incubation temperature and moisture limit the northern distribution of C. serpentina
The following was taken from the Status and Conservation section for the Snapping Turtle account in Maxell et al. 2009
Although this species is common in many parts of its range, it is rare in Montana, having been recorded in only a few watersheds of southeastern Montana. Due to this restricted range and the lack of information this species in Montana, it is considered a state species of concern, and is listed as sensitive by the Bureau of Land Management. Studies identifying or addressing specific risk factors for C. serpentina
in Montana are lacking. However, documented studies and other issues pertaining to their conservation include the following: (1) Roads often have negative impacts on population size and distribution of reptiles, and particularly turtles. High road density has been positively correlated to low population size. This has led to absence of species in road-developed areas and lead to local extirpations. (Rudolph et al. 1998, Jochimsen et al. 2004). C. serpentina
females often migrate over a kilometer to reach suitable nesting sites (Obbard and Brooks 1981a), which makes them particularly vulnerable to roadkill. During a three-year study in Ontario, Haxton (2000) noted that 30.5% of all turtles observed were killed on roads. (2) Snapping Turtles, particularly in northern populations take over 15 years to attain sexual maturity, have extended reproductive lifespans, high natural adult survival rates, and extended longevity. Egg and hatchling mortality is also often very high attributing to a low annual reproductive potential. These life history traits are typical of long-lived species vulnerable to adult mortality. Minimum levels of natural (e.g., winter kill) or human-caused mortality to mature adults can have serious negative impacts to populations. Due to this low reproductive potential, seriously diminished populations can take years to recover (Brooks et al. 1988, Brooks et al. 1991, Congdon et al. 1994, Congdon et al. 1995). (3) Snapping Turtles are a long-lived bottom dweller that can store environmental contaminants in their body fat, muscle tissue, liver, and eggs making them particularly susceptible to bioaccumulation. They often carry high concentrations of organochlorine contaminants such as polychlorinated biphenyls (PCBs) (Brooks et al. 1988, Harding 1997). (4) Popular for meat and soup dishes, C. serpentina
are managed as game animals in many states. Due to their low reproductive potential, overharvesting can decimate local populations, which can take years to recover (Brooks et al. 1988). Harvesting of adults is more detrimental to long-term population viability than high levels of egg and hatchling mortality, which normally occur. Human harvesting of C. serpentina
in Montana is not well documented but may occur where they are abundant. (5) Dams and large reservoirs on rivers (e.g., Fort Peck Dam and Reservoir) may inhibit population continuity to some degree, judging by the apparent lack of viable populations on the Missouri River in Montana (Maxell et al. 2003). However, there is no quantitative data to verify this. Snapping Turtles will travel large distances overland and therefore may be able to bypass some dams.
- Literature Cited AboveLegend: View Online Publication
- Aderhold, M. 1980. The 32-pound snapper of Redwater River. Montana Outdoors 11(4): 9-10.
- 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. 1970c. Turtles of Montana. Montana Wildlife, Montana Fish and Game Commission. Animals of Montana Series. 1970(Fall): 26-31.
- Black, J.H. and J.N. Black. 1971. Montana and its turtles. International Turtle and Tortoise Society 1971(May-July): 10-11, 34-35.
- Bobyn, M.L. and R.J. Brooks. 1994. Incubation conditions as potential factors limiting the northern distribution of snapping turtles, Chelydra serpentina. Canadian Journal of Zoology 72(1): 28-37.
- Brooks, R. J., D. A Galbraith, E. G. Nancekivell, and C. A. Bishop. 1988. Developing management guidelines for snapping turtles. In: R.C. Szaro, K.E. Severson, and D.R. Patton, technical coordinators. pp. 174-179. Management of amphibians, reptiles, and small mammals in North America. General Technical Report RM-166. U.S. Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado.
- Brooks, R. J., G. P. Brown, and D. A. Galbraith. 1991. Effects of a sudden increase in natural mortality of adults on a population of the common snapping turtle (Chelydra serpentina). Canadian Journal of Zoology 69: 1314-1320.
- Brooks, R.J., D.A. Galbraith, and J.A. Layfield. 1990. Occurrence of Placobdella parasitica (Hirudinea) on snapping turtles, Chelydra serpentina, in southeastern Ontario. Journal of Parasitology 76(2): 190-195.
- Brown, G. P. and R. J. Brooks. 1994. Characteristics of and fidelity to hibernacula in a northern population of snapping turtles, Chelydra serpentina. Copeia 1: 222-226.
- Brown, G.P., C.A. Bishop, and R.J. Brooks. 1994. Growth rate, reproductive output, and temperature selection of snapping turtles in habitats of different productivities. Journal of Herpetology 28(4): 405-410.
- Christiansen, J.L. and R.R. Burken. 1979. Growth and maturity of the snapping turtle (Chelydra serpentina) in Iowa. Herpetologica 35: 261-266.
- Congdon, J .D., A. E. Dunham and R. C. Van Loben Sels. 1994. Demographics of common snapping turtles (Chelydra serpentina): implications for conservation and management of long-lived organisms. American Zoologist 34: 397-408.
- Congdon, J. D., G. L. Breitenbach, R. C. Van Loben Sels, and D. W. Tinkle. 1987. Reproduction and nesting ecology of snapping turtles (Chelydra serpentina) in southeastern Michigan (USA). Herpetologica 43(1): 39-54.
- Congdon, J.D., A.E. Dunham, R.C. van Loben Sels, and J.T. Austin. 1995. Life histories and demographics of long-lived organisms: implications for management and conservation. U.S.F.S. General Technical Report. RM 264: 624-630.
- 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.
- Degenhardt, W. G., C. W. Painter, and A. H. Price. 1996. Amphibians and reptiles of New Mexico. University of New Mexico Press, Albuquerque.
- Dodd, C.K., Jr. and E.D. Brodie, Jr. 1975. Notes on the defensive behavior of the snapping turtle, Chelydra serpentina. Herpetologica 31: 286-288.
- Ernst, C. H., R. W. Barbour, and J. E. Lovich. 1994. Turtles of the United States and Canada. Smithsonian Institution Press. Washington, D.C. 578 p.
- Froese, A. D. and G. M. Burghardt. 1975. A dense natural population of the common snapping turtle (Chelydra serpentina). Herpetologica 31:204-208.
- Galbraith, D. A., M. W. Chandler, and R. J. Brooks. 1987. The fine structure of home ranges of male Chelydra serpentina: are snapping turtles territorial? Canadian Journal of Zoology 65(11): 2623-2629.
- Galbraith, D.A. and R.J. Brooks. 1989. Age estimates for snapping turtles. Journal of Wildlife Management 53(2): 502-508.
- 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.
- Hammer, D. A. 1969. Parameters of a marsh snapping turtle population, Lacreek Refuge, South Dakota. Journal of Wildlife Management 33(4):995-1005.
- Hammerson, G.A. 1999. Amphibians and reptiles in Colorado. University Press of Colorado & Colorado Division of Wildlife. Denver, CO. 484 p.
- Harding, J. H. 1997. Amphibians and reptiles of the Great Lakes region. University of Michigan Press, Ann Arbor. xvi + 378 pp.
- Haxton, T. 2000. Road mortality of snapping turtles, Chelydra serpentina, in central Ontario during their nesting period. The Canadian Field Naturalist 114(1): 106.
- 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.
- Iverson, J.B. 1991. Patterns of survivorship in turtles (order Testudines). Canadian Journal of Zoology 69: 385-391.
- Jochimsen, D.M., C.R. Peterson, K.M. Andrews, and J.W. Gibbons. 2004. A literature review of the effects of roads on amphibians and reptiles and the measures used to minimize those effects. Final Draft, Idaho Fish and Game Department, USDA Forest Service.
- 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.
- McKnight, C.M. and W.H.N. Gutzke. 1993. Effects of the embryonic environment and of hatchling housing conditions on growth of young snapping turtles (Chelydra serpentina). Copeia (2): 475-482.
- Meeks, R.L. and G.R. Ultsch. 1990. Overwintering behavior of snapping turtles. Copeia 1990(3): 880-884.
- Morris, K.A., G.C. Packard, T.J. Boardman, G.L. Paukstis, and M.J. Packard. 1983. Effect of the hydric environment on growth of embryonic snapping turtles (Chelydra serpentina). Herpetologica 39: 272-285.
- Obbard, M.E. and R.J. Brooks. 1980. Nesting migrations of the snapping turtle (Chelydra serpentina). Herpetologica 36: 158-162.
- Obbard, M.E. and R.J. Brooks. 1981a. A radio-telemetry and mark-recapture study of activity in the common snapping turtle, Chelydra serpentina. Copeia 1981: 630-637.
- Obbard, M.E. and R.J. Brooks. 1981b. Fate of overwintered clutches of the common snapping turtle (Chelydra serpentina) in Algonquin Park, Ontario, Canada. Canadian Field Naturalist 95:350-352.
- Obbard, M.E. and R.J. Brooks. 1987. Prediction of the onset of the annual nesting season of the common snapping turtle, Chelydra serpentina. Herpetologica 43: 324-328.
- Pell, S.M. 1940. Notes on the food habits of the common snapping turtle. Copeia 1940: 131.
- Pettit, K. E., C. A. Bishop, and R. J. Brooks. 1995. Home range and movements of the common snapping turtle, Chelydra serpentina serpentina, in a coastal wetland of Hamilton Harbour, Lake Ontario, Canada. Canadian Field Naturalist 109(2): 192-200.
- 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.
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