Chelydra serpentina

Shell hard, often with attached mud or algae; rear edge of upper shell saw-toothed; tail as long as or longer than carapace, with crest of large bony scales; head large, with hooked jaws; lower shell relatively small, composed of nine shields; limbs strong, with webbed toes and strong claws; maximum upper shell length nearly 50 cm, but usually less than 36 cm. Adult: upper shell relatively smooth, longitudinal ridges not very prominent. Mature male: anal opening farther from base of tail than in female, usually posterior to rear edge of carapace (under rear edge in female); grows to larger size than female. Juvenile: carapace with three longitudinal ridges. Hatchling: carapace rough, with conspicuous ridges, producing a cryptic dead-leaf-like appearance. Eggs: shell moderately pliable, somewhat brittle, with visible pores; 23-35 mm x 22-31 mm (average 28 mm x 27 mm). Source: Hammerson (1999).

Snapping turtles occupy all types of freshwater habitats (streams, lakes, reservoirs, ponds, marshes, swamps), especially those with soft mud bottoms and abundant aquatic vegetation or submerged brush and logs. They occur in brackish water in some areas. Usually they are on the bottom but sometimes bask out of water, especially younger individuals and in far north. Hibernation occurs singly or in groups in streams, lakes, ponds, or marshes; in bottom mud, in or under submerged logs or debris, under overhanging bank, or in muskrat tunnel; often in shallow water; sometimes in anoxic sites (Brown and Brooks 1994, Herman et al. 1995). Nesting occurs in soft soil in open areas, often hundreds of meters from water (up to 181 m from permanent water in Michigan, Congdon et al. 1987), sometimes in muskrat houses.

In Ontario, males occupied relatively stable, overlapping home ranges; summer range 0.4-2.3 ha (Galbraith et al. 1987). Also in Ontario, July-August foraging home ranges in three sites during one year were 2.3-18.1 ha (means fell between 5 and 9 ha); home range length was about 550-1990 m; home range size did not vary with habitat productivity (Brown et al. 1994). In another Ontario study, home range size over a year was 1.0-28.4 ha, averaging about 9 ha for females and about 2-3 ha for males (Pettit et al. 1995).

Frequently incurs high rates of nest predation (30-100% in Michigan) by various Carnivora (Congdon et al. 1987). See Iverson (1991) for a compilation of survivorship data (egg survival low, not more than 0.22; adult survival generally high, over 0.90). A population in Ontario, Canada, 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 otter predation on hibernating turtles; there was no compensatory density-dependent response in reproduction and recruitment (Brooks et al. 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).

Mating may occur any time during the warmer months. Snapping turtles in North America typically nest from late May to early July (mainly in June), but mainly from mid-June to early July in the far north. In dry regions, ground-softening rains often stimulate nesting. Clutch size averages 20-35, sometimes exceeds 100; 1 clutch/year in Michigan. Hatching and emergence from the nest typically occur about 2-3.5 months after laying, from late August to early October (most often in September), but sometimes the young do not emerge from the nest before winter.

Snapping turtles commonly experience low reproductive success due to extensive predation on their eggs, but females produce large clutches and may live and reproduce for several decades, so eventually they produce offspring that join the breeding population. In Michigan, nest survivorship over 17 years ranged from 0 to 64% and averaged 23% (Congdon et al. 1994). In Ontario, growth rate and reproductive output increased with habitat productivity (Brown et al. 1994). In Michigan, minimum reproductive frequency was less than annual (0.85) (Congdon et al. 1994).

Females are sexually mature in about 8 years in Iowa, 10-20 years in Ontario (later in north than in south), 11-16 years in southeastern Michigan (Congdon et al. 1994); also in Ontario, mean age of first nesting estimated at 17-19 years (Galbraith et al. 1989). In Ontario, the mean age of nesting females was estimated at 33-40 years (Brooks et al. 1988, Galbraith and Brooks 1989).