The Staying Power of Snapping Turtles
Sure, snapping turtles are sometimes irascible and always prehistoric-looking. But these relics, which have been around for 90 million years, are the ultimate survivors.
Running across the Dartmouth College campus in Hanover, New Hampshire, around the western edge of Occum Pond, I spot a tiny snapping turtle alongside the road, motionless as if contemplating its future, which would have included trying to cross the road had I not intervened. The turtle is black, the size of a half-dollar, all legs and tail and neck (even at this tender age). Its eyes are mustard-colored, bright and inquisitive, its face hawklike, though it doesn't snap as I hold it between thumb and forefinger. On the turtle's cross-shaped lower shell, called the plastron, is a soft yellow oval with a tiny vertical slit, the remnant of the yolk sac and its omphalic connection to the hatchling, a mother turtle's only investment in her offspring besides her placement of the nest. The carapace, or upper shell, is crenellated, the margins spiky; three rows of sharp little points run down its middle like an archipelago. Unlike a box turtle, there's not much room for a hatchling snapper to withdraw into its shell, the chelonian equivalent of being born too big for your breeches, a lifelong morphological fact that may contribute to an adult snapper's irascible disposition on land.
When I release the snapper into Occum Pond, it sinks into the ooze and then swims away, a plume of silt trailing behind, an easy meal for an aquatic predator--bass, pickerel, bullfrog, or heron--and maybe one reason a female snapping turtle lays a clutch of 26 to 55 eggs (sometimes more than 100) each year beginning at age 11 or 12 in the Northeast and continuing for 20 years or more. (Snapping turtles in South Florida may breed more than once a year, partly because there is no need for hibernation in the steamy subtropics and maybe partly to compensate for heavy losses to the snap-trap jaws of hungry alligators.)
"Turtles are a kind of bird with the governor turned low," wrote Edward Hoag-land, a reference to their lethargy (and longevity). In my corner of the Northeast, snapping turtles hibernate five or six months a year, dreaming turtle dreams tucked beneath a blanket of anoxic mud in the weedy, eutrophic shallows of ponds, marshes, and lakeshores, their pilot lights barely flickering. The ability to endure exposure to low levels of dissolved oxygen permits snapping turtles to winter in sites that are off-limits to wood turtles, which need much higher levels of dissolved oxygen during dormancy. Consequently, snapping turtles are far more common and far more commonly encountered than wood turtles. They're most often seen in late spring, when females search for nest sites, and in early autumn, when hatchlings like the one I ferry to Occum Pond emerge from their earthen wombs to negotiate a gauntlet of terrestrial predators, including everything from chipmunks to crows to shrews, on their way to water.
The snapping turtle family, Chelydridae, evolved in North America and has haunted our wetlands almost unchanged for nearly 90 million years. Ancestors spread to Eurasia about 40 million years ago and then disappeared from that continent in the late Pliocene, about two million years ago. Chelydrids have been sequestered in the Western Hemisphere ever since, which makes them among our truest and oldest turtles. They were present when dinosaurs lived and died, and had been laying round, white, leathery eggs in sandy loam and glacial till for millions of years when the first Amerindians wandered over the Bering Land Bridge. Snapping turtles have witnessed the drift of continents, the birth of islands, the drowning of coastlines, the rise and fall of mountain ranges, the spread of prairies and deserts, the comings and goings of glaciers.
They range across southern Canada from Alberta to Nova Scotia, throughout the eastern two-thirds of America from the apron of the Rocky Mountains east to the tidewater Atlantic, and south to the Gulf Coast and the Mexican tributaries of the Rio Grande. Two sibling species dwell in the tropics--one ranging from the Atlantic lowlands of Vera Cruz, Mexico, to Honduras, and the other from Nicaragua south through Caribbean Central America to the Pacific coast of Colombia and Ecuador. Like their northern cousin, both species seek mud-bottomed, weed-choked wetlands, and are opportunistic feeders, dining on whatever is available: carrion, aquatic invertebrates, fish, amphibians, other turtles, small mammals, snakes, the occasional bird (ducklings usually), and all manner of aquatic plants, which may make up more than half their diet.
As is the case with rattlesnakes, the snapping turtle's reported nature is addled by exaggeration, and no characteristic is more hyperbolized than its bite. Googling "snapping turtle" yields results that highlight human misperceptions of this big, bigheaded chelonian, the beast with an iniquitous, but mostly undeserved, reputation. When I was growing up on Long Island, suburban legend claimed that a large, hatchet-faced snapping turtle--common in streams, sumps, and tidal marshes along the South Shore--could break a broom handle in one bite. Years later I tested the hypothesis, which proved false.
A few years ago the blog BirdForum, for example, ran a dialogue called "Are snapping turtles killing our birds?" Someone whose mother blamed the much-maligned turtle for a reduction of geese on a local lake inquired, "Do snapping turtles actively hunt down adult-sized Canadian geese?" One correspondent suggested that the fleshy lure on the tongue of the snapping turtle (actually the lure is on the tongue of the closely related but much larger alligator snapping turtle, of the Mississippi drainage) attracts geese. The curious goose then gets "its head chomped on my [sic] the turtle."
Snapping turtles, whose jaws are more clamps than guillotines, do occasionally take birds. I found a note online in Volume 108 of The Wilson Bulletin titled "Observations of shorebird predation by snapping turtles in eastern Lake Ontario." The author reports on a turtle that left an inland pond and crossed a sandy beach besieged the whole way by large numbers of angry shorebirds until the snapper entered Ontario and disappeared beneath a floating carpet of algae. Why were the birds riled? In late summer, when lake shallows heat up, large submerged mats of filamentous green algae rise off the bottom and drift. Teeming with invertebrates and small fish, the mats are a floating buffet for migrating shorebirds. Snapping turtles, classic ambush predators, lurk beneath the algae pulling hapless sandpipers through by their feet, an event the author witnessed on three occasions.
Once when I was in northern Virginia, a biologist friend told me of a snapping turtle that grabbed a great blue heron by the leg and then towed the protesting bird into deep water. The turtle sank to the bottom--part anchor, part vise grip--drowning the heron, which it presumably ate. More than 30 years ago, when I was an Audubon biologist monitoring New Hampshire's loon population, residents along the shore of Lake Conway claimed a loon family had lost two chicks down the maw of a snapping turtle. I visited the lake and found several sink-sized turtles sprawled on the surface sunbathing, as though they had bubbled up from the depths like the Lake Ontario algae mats.
To learn about the nesting habits of snapping turtles, I visit wildlife artist David Carroll, whose books include Year of the Turtle and Self-Portrait With Turtles. Carroll is coiffed in gray from chin to crown, casual and energetic, a man who feels deeply about turtles and the fate of their diminishing habitat in the Northeast. When he was 10, he discovered how fast a snapping turtle can strike and how far it can stretch its serpentine neck. An irate turtle opened three of his fingers, although, says Carroll, "I deserved it. I was poking it in the nose with a stick." Undiminished by the experience, Carroll works with state and municipal governments, the Nature Conservancy, and land trusts to preserve critical turtle habitat. A renaissance man who hobnobs with scientists and artists, writers and scholars, Carroll has taught school, plays competitive Wiffle Ball, and has studied the same community of turtles--six different species, including snappers--for more than 30 years. Until he received a MacArthur grant in 2006, he survived on a shoestring with his wife, Laurette, also an artist, producing exquisite watercolor paintings for a series of books.
Carroll takes me to his study site, a sandy pumpkin field at the junction of two streams, a mile from a sizable river in south-central New Hampshire. He prefers not to name the river, because turtle poaching is a serious problem in the Northeast, particularly with wood, spotted, and Blanding's turtles. It's early June, well before noon. The sky is cloudless, the day already cooking. The pumpkin field is warm, a vital consideration for a mother snapping turtle choosing a nest site.
Between mid-May and late June, female snappers disperse upstream from shallow ponds and marshes, sometimes for weeks, looking for well-drained, exposed ground, anywhere the sun hits for the majority of the day--blowdowns, fields, west-facing roadsides, sandbanks and dunes, construction sites, muskrat and beaver lodges. A snapping turtle may even use an ephemeral stream as a route to its nesting site, its shell above the water. Males patrol deeper streams, necks craned, scouting for mates. Territorial disputes between ardent males are cumbersome affairs, and they splash and thrash and shove like aquatic Sumo wrestlers. Several times I've mistaken these battles royal for mating, which Carroll says is more delicate.
At the field's edge are two parallel ridges of sand eight or nine inches long and two or three inches high. A slight depression between them angles downward, and perpendicular to their lower end is the print of a long, well-muscled tail. Eggs lie below the depression. "If you want to see a snapping turtle nest," says Carroll, "go out on a rainy early morning in June." I did that once along a brook near my home and found a turtle leaning out of her little sand pit. She ignored me as I sat there for an hour watching each ping-pong-ball-size egg fall into the pit. Finished, she used her oversized hind feet to spray sand on the eggs, covering the pit, and left for the nearby brook, her personality morphing from oblivious to bellicose, snapping at anyone or anything that might interfere with her return to the safety of water.
I remember that turtle as I look at the pumpkin-field nest and imagine this turtle locked in her own egg-laying trance, skunks and raccoons--the principal nest predators in the Northeast--licking their chops in anticipation of an easy meal. "It's a wonder any eggs hatch," says Carroll, as he points to a pile of eggshells, the remnants of a nest predated a couple of days before.
A young snapping turtle's fate depends upon its mother's choice of a nest site, which determines both a hatchling's size--moist earth produces larger embryos than dry earth--and its sex. Known as temperature-dependent sex determination, or TSD, the temperature of each egg midway into the first trimester of incubation influences a hatchling's sex, a trait shared with all crocodilians, many other turtles, and several lizards. Under the southern sun, which might shrivel the eggs, snapping turtles nest in the shade. Here, in the cooler Northeast, they seek full sun. Although there are TSD differences across the snapping turtle's broad geographic range, mostly males develop at temperatures between 70 and 75 degrees Fahrenheit and mostly females above 84 degrees or below 70 degrees. A clutch of eggs may produce mostly females on top, where it's warmest, and on the bottom, where it's coolest, while males dominate in the middle of the nest. Nests with a uniform temperature may yield a single sex.
Carroll sees a snapping turtle's life, even that of the biggest, scariest-looking turtle in the pond, as filled with obstacles. Hibernating snapping turtles, with some of their meaty anatomy exposed, are inviting targets. Otters, Carroll says, root out these comatose and defenseless victims and chew off their legs and tails.
Avoiding prowling humans is another story. People hunt and trap large snappers for their meat, of which there is plenty. In the Midwest and South, there's a large commercial market. Historically, Carroll tells me, snapping turtle soup was popular in Philadelphia, and it still is in some places. When I attended college in Indiana, I bought a can of turtle soup in a local grocery just to give it a try, but it proved to be bland.
"I've never eaten it," Carroll says. "I can't eat my brothers."