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.
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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.
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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.
