Montana Field Guide

EGGS:
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).

HATCHLINGS:
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).

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).

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.