Western Pond Turtle

Western Pond Turtle

Natural History

The western pond turtle (Clemmys marmorata), also known as the Pacific pond turtle or Pacific mud turtle, is the only fresh-water turtle native to the North American Pacific Coast west of the Sierra-Cascade divide, with the exception of the Sonoran mud turtle (Kinosternon sonoriense) constrained to the southeast corner of California. The literature describes two subspecies of western pond turtle; the northwestern pond turtle (C. m. marmorata) found from the area north of the American River, and the southwestern pond turtle (C. m. pallida) found from the coastal area south of San Francisco. A zone of intergradation occurs between the two subspecies from the San Joaquin Valley to the south and east San Francisco Bay Area. A third potential subspecies from the Columbia Gorge in Oregon remains undescribed.

 

The specific name "marmorata" is in reference to the marbling pattern evident on both the carapace and skin. Throughout their range, however, the colors and markings of western pond turtles vary ontogenetically, geographically, and sexually. As they age, hatchlings darken in coloration, and as adults they lose their marmorate markings. The southern subspecies C. m. pallida is lighter in coloration, and exhibits a greater contrast between the color of its shell and dorsal skin than does its northern counterpart. In general, the ground color of the pond turtle's shell ranges from a light yellow (especially in C. m. pallida) or brown to a black. Some carapaces are unmarked, while others are marked with dark vermiculation patterns or fine black or dark brown lines. Underneath, the plastron ranges in color from cream to pale yellowish to a light brown, with a portion of the plastron covered in a dark mottling.

The historic range of the western pond turtle along the Pacific coast ranged as far north as Klickitat County, Washington, and as far south as northern Baja California, Mexico. In 1996, it was estimated that Washington State supported three isolated populations of pond turtles in Klickitat, Skamania, and Pierce County totaling 311 turtles. The species is found in greater numbers through Oregon and California, although throughout its range, especially the San Joaquin Valley and southern California, populations are on the decline and recruitment is limited. Most historical populations in Baja California have been extirpated.

Overall, western pond turtles have been described as habitat generalists. Pond turtles have been observed in slow-moving rivers and streams (e.g. in oxbows), lakes, reservoirs, permanent and ephemeral wetlands, stock ponds, and sewage treatment plants. Western pond turtles prefer aquatic habitat with refugia such as undercut banks, submerged vegetation, rocks, logs and mud banks, and have been known to avoid areas with open water that lack refugia. Being ectotherms, pond turtles require emergent basking sites to thermoregulate their body temperature, taking advantage of mud banks, rocks, logs, root wads, and other opportunistic sites.

Despite their name, pond turtles regularly utilize upland terrestrial habitat, most often during the summer and winter, especially for oviposition (females), mate seeking (males), overwintering, aseasonal terrestrial habitat use, and overland dispersal. Most often overland movement events are part of normal turtle movements within a terrestrial home range, but pond turtles regularly overwinter in uplands, burying themselves beneath the leaf litter.

Throughout their range, adult pond turtles are active year-round, although farther north their activity can be limited. In winter, pond turtles often hibernate in the soft muddy bottom of a stream. On land, they move upland in search of hibernation sites. Those adults that overwinter do so between late September and late November. In the spring months, they emerge from between March and June, depending on their geography and the variation in temperature conditions.

When feeding, pond turtles seek out food by sight or smell. Since they are unable to swallow food in the air, they must ingest their prey in the water. They have also been observed engaging in neustophagia (modified filter feeding), wherein they "gape-and-suck" small invertebrates out of the water column. Their omnivorous diet includes adult and larval aquatic insects, terrestrial grasshoppers and aerial flies off the water's surface, beetles, fish, worms, crustaceans, amphibians (egg masses, tadpoles and adults), and - infrequently - aquatic plants, including algae, yellow pond lily fronds, willow and alder catkins, inflorescences, tule, and cattail roots. Although it is questionable as to whether larger vertebrate prey is captured alive or eaten as carrion, pond turtles have been noted to scavenge on the carcasses of mammal, bird, reptile, amphibian, and fish species.

Common predators of nests, nested hatchlings, and adult turtles in the wild include raccoons (Procyon lotor), skunks (Mephitis mephitis), and coyotes (Canis latrans), although the largest threats western pond turtles face presently are the predation of hatchlings by introduced, non-native bullfrogs (Rana catesbeiana), and the loss of habitat due to urbanization.