Breeding occurs in late spring to mid-summer (4), with mating taking place under water (5). Most mature females nest every year, some laying two clutches per season (5). In early summer the eggs are deposited in the nest, which is generally dug in soil, close to a water source, but some females may dig their nests many metres away from the water’s edge (9). The female lays an average of four to seven eggs (range 1 to 13) per clutch, which hatch after approximately 13 to 17 weeks (4); however, hatchlings from northern California northward over-winter in the nest (10). Western pond turtles develop slowly in areas with short or cool summers, taking up to eight years to reach sexual maturity. They can grow relatively fast in warmer regions and in some nutrient-rich habitats, where they can reach maturity in half that time (4). Turtles are thought to live up to 40 years (5).
Adults face predation by a number of carnivores including racoons, otters, ospreys and coyotes. Hatchling turtles, being small with soft shells, are easily preyed upon by raptors, ravens, weasels, bullfrogs and large fish. The diet of the western pond turtle includes some plants, small fish, frogs, carrion and, most importantly, aquatic insects and larvae (4). Western pond turtles bask on mats of floating vegetation, floating logs or on mud banks just above the water’s surface. In warmer climes they engage in aquatic basking by moving into the warm thermal environment in or on top of submerged mats of vegetation (4).