Snapping Turtles Meet Their Match

snapping-turtle-bryan-pfeifferAt first I thought the big black shape in the lane was a piece of burst tire. Then the tire held out a slow, prehistoric foot and took a step. Its long neck shifted into view as I drove by, and I realized it was a huge snapping turtle. In the few seconds I’d been watching, several cars had already whizzed past, missing it by inches. It was halfway across the first of eight lanes of traffic it would need to traverse to reach the other side of I-93.

I don’t normally cry over road kill. But a mile down the road I pulled into the breakdown lane and burst into tears. I imagined a cop stopping to help with the emergency and discovering, inside the Subaru Forester with, of course, Vermont plates, a young woman sobbing over a turtle who last she saw was unharmed.

The futility of its journey had overwhelmed me. The turtle, moving with the confident plod that has served its species for 40 million years, had looked so out of its element on the highway. It had completed only a fraction of an impossible crossing. This creature, steadfastly putting one foot in front of the other, was utterly screwed.

Early each summer, snapping turtles leave the water to lay eggs on land, traveling up to four miles from home. The one I saw last June may have been a mother looking for a good spot to dig a nest, or a young turtle dispersing from its original home range. Unlike most animals, female snapping turtles disperse over greater distances than males and keep similarly sized home ranges (eight acres on average, in the north). Some nomadic females have no home range at all; others return to the same nest site annually. Since they can retain sperm in their bodies and use it over multiple seasons, they do not need to mate every year.

This strategy has worked well for Chelydra serpentina—so well that it is the ancestor of 80 percent of all living turtles. In fact, snapping turtles have hardly changed in appearance from the earliest turtle, which evolved over 200 million years ago. In other words, proto snapping turtles had already been around for 150 million years when Tyrannosaurus rex appeared on the scene.

Having survived two major extinction events in close to their current shape, modern snapping turtles faced virtually no predators once full grown until a century ago, when the automobile was invented. Now most females living in developed areas die on roads after only a few nesting seasons. Their natural life spans, although they average 30 years, can last over 80 years. In other words, the individual I saw on I-93 could have been older than the highway itself.

This time of year, snapping turtles have buried themselves in the mud of a pond, swamp, or slow-moving stream and begun hibernation, deep enough that the mud around them will not freeze. While they often do spend the winter within their home range, they can travel up to two and a half miles away to hibernate and then return to their territories in the spring. Individuals sometimes stay faithful to a few particular hibernacula, rotating between them year after year. If a site becomes popular, turtles can end up stacked on top of each other for the winter. This group hibernation makes them vulnerable to occasional predation by otters.

Still, I think a turtle stands a better chance unconscious against an aquatic carnivore than crossing an interstate highway. I can only hope that my turtle had already laid her eggs and was on the way back to her pond. Perhaps her hatchlings, if not she herself, now lie safe in the mud, waiting till spring.

Sonia DeYoung is a second-year student in the Field Naturalist Program.

Information gathered from “Snapping Turtles” by Susanne Kynast on The Tortoise Trust website, Naturally Curious by Mary Holland, and Animal Diversity Web.

Partial Migrants: Should I Stay or Should I Go?

Outside my window, a robin pecks around in the rain. It’s the day before Thanksgiving, and the forecast calls for the rain to turn to snow tonight in my Massachusetts hometown. So why isn’t this robin right now flying south toward a warm, easy winter?

American robins are facultative partial migrants: they decide each year whether to migrate

American robins are facultative partial migrants: they decide each year whether to migrate

Casual birdwatchers see robins as harbingers of spring, but you can actually find them year-round throughout much of the U.S. Based on my own observations, robins seem to stick around more now than they did twenty years ago—perhaps global warming plays a role in that trend (see November 6 post). But climate change can’t explain why some robins flee wintertime and others take their chances.

[Update: The day after publishing this post, I stumbled across an article by biologist Mark Davis saying that more robins stay in the north for the winter now because of a greater winter food supply: they happily eat the berries of several increasingly common non-native species.]

Many birds, like warblers and hummingbirds, migrate annually no matter what. Others, including robins, kingfishers, and chickadees, are “partial migrants”: within a single population in a given year, some will migrate and some will not. Backyard birdwatchers who rejoice in the first robin of spring aren’t necessarily unobservant. There are fewer robins around in winter, and those that do stay often roost in bogs and swamps instead of backyards. Each year, a robin must decide based on the available food supply whether to migrate; a snowy winter landscape can never provide as much food as the same land in summer. Some robins may even leave mid-season if the conditions turns especially harsh. Continue reading

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