Western Pond Turtle – The Egg Drop

A female western pond turtle.

The western pond turtle (Clemmys marmorata), the Pacific Coast’s only native freshwater turtle, inhabits the waters of the West’s rivers, streams, and ponds. There in the shallows and murky depths, they bask and forage from spring to late fall, their everyday needs met in a watery world where escape is a skittering “splash” away. But every year at about this time, as the days draw long and warm, females gravid with eggs venture from the safety of these waters to dry land in search of a spot to nest.

For nine years running, I’ve set aside time each June to stalk western pond turtles during the height of their nesting season. With each passing year, I learn something new about their behavior, stumbling sometimes into an instance where I witness something few are fortunate enough to see. One year it was discovering an intact egg left behind in a turtle nest that had otherwise been picked clean by an unknown predator; another year, it was watching a female abandon a nesting attempt because of an ill-placed rock only to see her return three days later in a rather circumambulatory route to successfully nest within inches – inches! – of the original failed nest-scrape. Last year, as I was crouched behind a manzanita bush watching one female meandering through a meadow in search of a nest site, a second female trundled out of the woods behind me and, with only a few moment’s hesitation, proceeded to scape a nest within five feet of where I knelt (she hit a rock and had to abandon her attempt).

This year, I twice walked up on females as they laid their clutches of tiny eggs. The second time, I was so close that, despite the chorus of red-winged blackbirds, I could hear the scrape of shell as each egg tumbled into the nest (see the video below).

VIDEO: Western pond turtle laying eggs.

For a turtle, nesting is no simple task; the act of digging a nest far from the water’s edge is executed at great risk to the female. Relying on queues we have yet to understand, gravid females head for shore late in the afternoon to nest. Like the proverbial fish out of water, the moment a turtle sets foot on dry land, she’s at the mercy not only of predators (which can feast on both her and her clutch of eggs), but the extreme summer heat, the onset of nightfall (which can cut short the nesting process and leaves her vulnerable), and the risk of having to abandon a nesting attempt if she hits a rock or root. Her only protection during this overland ordeal is to abandon her nest, retreat inside her shell, and return to the water. And then to try, try again.

The start of a western pond turtle nest – abandoned due to a large rock in the ground.

A western pond turtle laying an egg.

The western pond turtle’s nest is a Spartan thing – little more than a pear-shaped cavity excavated in the hard earth. After choosing a nest site, the female first pees on the ground to loosen the soil and then begins to scrape a hole into the ground with her hind legs. Over time, the hole becomes the neck of the nest chamber, which she expands into a cavity up to 125 mm (~5 inches) deep. Once the chamber is complete, the female begins laying anywhere from 1 to 13 eggs, which she carefully arranges in the nest with her hind limb as each is laid. With the eggs in place, the female back-fills the neck of the nest chamber with mud, leaves, and grasses, forming a plug that becomes indistinguishable from its surroundings as quickly as the mud takes to dry.

Western pond turtle eggs in a newly dug nest.

A typical western pond turtle egg is hard-shelled like a bird’s egg (rather than leathery), elliptical-to-oval in shape, and matte-white, with an average size of 37 mm (1½ inches) long, 20 mm (¾ inches) wide, and around 8 grams in weight, the approximate size of a quail egg.

Western pond turtle eggs recovered from a depredated nest (with a penny for scale).

Depending on the clutch size and any obstacles met along the way, the entire nesting process can take a turtle from as little as an hour to an entire evening. But – success or failure – if evening falls before the female can return to the water, she’ll instead wander away from the nest in search of some leaf litter or a shrub to hunker down under for the night, waiting until dawn to make for the water.

Every year – sometimes twice in a season (a feat known as double-clutching) – mature females repeat this ritual with uncanny precision. Some females exhibit nest-site fidelity, whereby they head for the same site year after year to nest; for other females, it is still unclear how or why they select certain sites. Despite the care with which each nest site is selected and the eggs laid, maternal care ends there; females return to their rivers and ponds.

Eight to 100 days after the nest is laid, hatchling turtles will break free from their shells. Depending on their locale, the earth will stir once more with hatchlings emerging from their nests – either in the fall or, in colder climates, in the spring after the young overwinter in the nest. Instinct will lure these tiny turtles to the waters they’re to call home. And six years later, the females that survive to maturity will retrace their mother’s footsteps – how closely, we still don’t know – to recruit the next generation of turtles.

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  1. Western Pond Turtle – From Hatchling to Head Start « (bio)accumulation

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