Actinemys marmorata (Baird & Girard, 1852)

Common Name and Taxonomic History

Actinemys marmorata, commonly known as the northwestern pond turtle (previously classified together with the southwestern pond turtle Actinemys pallida as the single western pond turtle species), has a distinct physical description.

Dorsal Coloration

Its dorsal surface is usually dark brown or dull olive, and may or may not have darker reticulations or streaking.

Plastron Coloration

The plastron is yellowish, and sometimes has dark blotches at the center of each scute.

Carapace Length

Adult straight carapace length ranges from 11–21 cm (4.5–8.5 in).

Carapace Structure

The carapace is low and broad, usually widest behind the middle; adult carapaces are smooth, with no keel or serrations.

Sexual Dimorphism

Adult western pond turtles are sexually dimorphic: males have a light or pale yellow throat.

Historical Range

This turtle originally ranged from northern Baja California, Mexico, north to southern British Columbia, Canada.

Historical Fishery Use

Historically, it was a major part of a fishery on Tulare Lake, California, where it supplied turtle soup, a popular local food, to San Francisco, and was used as feed for hogs that learned to dive for the turtles in the shallows of Hog Island on Tulare Lake.

Washington Population Status

As of 2007, the species has become rare or entirely absent from the Puget Sound region of Washington. It has a disjunct distribution across most of the Northwest, and a small number of isolated populations remain in southern Washington.

Oregon Population Status

It is now rare in the Willamette Valley north of Eugene, Oregon, but becomes more abundant south of Eugene where temperatures are higher, and may be locally common in some streams, rivers, and ponds of southern Oregon.

Cascade Range Occurrence

There are a few records of the species east of the Cascade Mountains, but these are thought to refer to introduced individuals.

Elevation Range

Its elevation range goes up to 305 m (1,001 ft) in Washington, and to about 915 m (3,002 ft) in Oregon.

California Distribution

It also occurs in the Uvas Canyon area of the Santa Cruz Mountains, California, the California North Bay, and in lakes such as Fountaingrove Lake.

Taxonomic Split

Many taxonomic authorities have split what was once considered a single western pond turtle species into two: the southern Actinemys pallida (southwestern pond turtle), found in southern California and Mexico, and the northern Actinemys marmorata (northwestern pond turtle) ranging from northern California northward.

Aquatic Habitat Types

Actinemys marmorata lives in both permanent and intermittent bodies of water, including marshes, streams, rivers, ponds, and lakes.

Basking Behavior

It prefers habitats with abundant emergent logs or boulders, where individuals gather to bask; they also bask on top of aquatic vegetation, which means the species is often overlooked in the wild.

Observation Tips

Slow movement and hiding behind trees and shrubs can allow observers to spot resident turtles. A. marmorata can be encouraged to use artificial basking substrates, or rafts, which makes it easy to detect the species in complex habitats.

Terrestrial Habitat Use

Terrestrial habitat is extremely important for this species: many intermittent ponds dry out during the summer and fall along the west coast, especially during drought, so A. marmorata can spend more than 200 days out of water.

Overwintering Behavior

Many individuals overwinter on land, and often create their annual nests during this overwintering period. Overwintering sites can sometimes be located 500 meters from the nearest main body of water.

Clutch Size

Sexually mature female northwestern pond turtles lay 5–13 eggs per clutch, and can deposit clutches once or twice a year.

Nesting Distance from Water

Females may travel a significant distance from water to lay eggs, moving as far as 0.8 km (1/2 mile) away from the nearest water source and up to 90 m (300 ft) above it, though most nests are located within 90 m (300 ft) of water.

Nest Site Selection

Females usually leave the water in the evening and may wander a long distance before choosing a nest site, which is typically an open, south-facing area of sand or hardpan.

Nest Structure

The nest is flask-shaped, with an opening around 5 cm (2 in) across.

Nest Concealment

Females spend a lot of time covering the nest with soil and nearby low vegetation, making the nest very hard for people to find unless it has already been disturbed by a predator.