Wild Side: Box turtles, private but vulnerable, do well on Martha’s VIneyard

Wild Side: Box turtles, private but vulnerable, do well on Martha’s VIneyard

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A female box turtle laying eggs by burying them where, unfortunately, they are easy for skunks and raccoons to find. — Photo by Matt Pelikan

The Vineyard, sadly, is not endowed with much variety when it comes to turtles. One species, the painted turtle, is abundant here, occupying nearly every freshwater pond on the Island. Another, the snapping turtle, is uncommon but widely distributed, growing to disconcertingly large size in some bodies of water. The diamond-backed terrapin, a threatened species restricted to salt marsh, is theoretically possible here but is almost certainly absent. And spotted, musk, and Blanding’s turtles are all either here or not, depending on your source, but if present they are rare enough so I’ve never seen them in the course of 16 years of very active field work on the Island.

Which leaves my personal favorite, the eastern box turtle. While its Massachusetts distribution is quite broad, its numbers appear to be declining statewide, and the state’s Natural Heritage program lists it as a Species of Special Concern. It is uncommon and probably declining on the Vineyard, too, but we have a lot of suitable habitat for this species, and they are out there: the Island probably represents the closest this excellent reptile has to a stronghold in the state.

Box turtles are easily recognized by their high, domed shell, the shape of which gives this animal its name. The black ground color of the shell is variably mottled with orange or yellow markings, and the head and neck follow the same color scheme. Habitat provides a useful clue for identifying this species, too: it is a turtle of woods and edges rather than ponds, occupying moist woodland, oak woods, and the edges of scrubby, overgrown fields. The vast majority of the Vineyard’s box turtles probably occur in the up-Island towns, with the species unlikely to be encountered in the dry sandplain of our central and southeastern regions.

Like other turtles, the box turtle is a stately creature, moving at a dignified pace through its daily routine and indeed through its long life span (box turtles may live for decades, though they grow slowly and rarely reach a length much greater than about six inches). Their slow movements make them easy to overlook, and in a wooded habitat, their mottled shells resemble speckles of sunlight, helping them stay unseen. When a box turtle finds itself discovered, though, it finds effective protection in its robust shell: the lower shell is hinged, helping the turtle form an effective seal around most of its vulnerable head.

Clearly, though, a benign temperament and a thick shell haven’t sufficed to keep this animal common here, and the causes are easy to surmise. For one thing, box turtles are notoriously prone to getting mashed by cars. I’ve never seen a road-killed one on the Island, but that’s because most of them had already been flattened before I moved here.

These turtles do not to range very widely. Some sources report they spend most of their lives within a radius of a few hundred yards, and most of our remaining box turtles probably live in tracts of woodland large enough so that the turtles never feel the need to cross a road. This species, in other words, is a good illustration of the negative results of habitat fragmentation, and, correspondingly, the importance of maintaining large, undisturbed patches of habitat.

Female box turtles typically lay fewer than a half-dozen eggs in a shallow hole that they scrape in the ground, and herein lies another problem for these turtles. Skunks and raccoons readily find, excavate, and eat the eggs. Because the populations of these mammalian predators are boosted to artificially high numbers by human activity (our garbage may be their main food source), box turtles are under more pressure from this threat than would naturally occur.

Box turtles, then, offer a classic example of a lifestyle that doesn’t translate well to the modern world. In theory, a female only needs to produce two young that live to maturity in order to replace herself and her mate. And this species has evolved a pattern of long life but low fecundity to achieve this rate of reproduction. Such species are highly vulnerable to loss of adults. Short life and low fecundity clearly won’t do the job, and they are also vulnerable to factors (like predation of eggs) that reduce breeding success. Building roads and encouraging skunks, we’ve produced a “perfect storm” for the box turtle.

Like all our turtles, box turtles are harmless animals that help maintain the balance of nature through their consumption of slugs, snails, other invertebrates, and plant material. (Even the fearsome-looking snapping turtle is a beneficial animal, dangerous only if you pester it, and should be left alone.) When you drive, remain alert for wildlife crossing the road. If you mow in brushy habitat, do your best to keep an eye out for box turtles. And if you find a box turtle or its nest, enjoy a quick, appreciative look and then make yourself scarce. You’re the turtle’s worst nightmare.