Wild Side: Turkey vultures have taken hold on Martha’s Vineyard

Wild Side: Turkey vultures have taken hold on Martha’s Vineyard

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With a wing span reaching six feet and a broad tail, turkey vultures can ride thermal up-drafts indefinitely, using their primary feathers to make minute adjustments — Photo Courtesy of U.S. Fish and Wildlife

A rarity on the Vineyard not so long ago, the turkey vulture has grown steadily in numbers here over the last couple of decades, and we now have a smallish but conspicuous year-round population. While its personal habits win few admirers, this massive carrion-eater is a marvel of ornithological engineering, perfectly designed for its manner of living. And its status here presents enough mystery to make this bird worthy of more attention.

They’re hard to miss, here or indeed anywhere else in their vast geographical range, which extends from southern Canada to the farthest tip of South America. Like all vultures, these are big birds, weighing about four pounds and having broad wings that span about six feet when fully spread. Turkey vultures are typically seen overhead, soaring on motionless wings that are slightly raised into a shallow vee, a profile recognizable from a vast distance. The primary feathers — the large ones at the tip of the wing — are likewise broad and solid. Watch a vulture carefully in flight and you can see it making constant, precise motions with these feathers — little aerodynamic tweaks for maximum efficiency.

These birds are splendidly designed for soaring, able to ride updrafts for hours. But for all their grace in a thermal, on take-off they labor to flap their wings in slow, rolling strokes, almost painful to watch and totally different from the snappier wing-beats of a red-tailed hawk or even an eagle. From a distance, “TVs” appear all black with slightly paler flight feathers on their wings; with a better look, you’ll note an unfeathered head, dark brown on young birds but bright red on adults.

That bare head is probably a good place to start in discussing the habits of the turkey vulture. Though generally grouped with hawks and eagles, vultures lack the powerful feet and sharp talons of those feathered assassins, and vultures seldom or ever kill their own food. But they’ll eat nearly anything that something else has killed. For Vineyard vultures, this probably means road kill of any kind, gut piles during deer-hunting season, and a side-order of garbage. The bare head — an adaption shared by vultures generally — is simply designed to stay clean while its possessor is poking around for good bits inside a well-ripened body cavity.

Once carrion heads down the hatch, it encounters a vulture’s industrial-strength digestive system. The intestinal secretions of a turkey vulture make short work of nearly anything, but the contents of a vulture’s digestive tract serve a couple of functions that you might not expect. Self-defense, for one: corner a vulture and it will vomit its latest meal, mixed with highly acidic digestive juices, all over you. I bet you’ll back off. And thermal regulation, for another: when overheated, vultures defecate on their bare legs, and the cooling effect as the droppings evaporate lets the legs dissipate heat like a car radiator.

Happily, turkey vultures are bashful birds, and getting close enough to witness these unappealing habits is difficult. These are hard birds to study: while their numbers and year-round presence suggest that turkey vultures are nesting here regularly, only a few nests have ever been found on the Vineyard, and the questions of where on the Island they’re nesting and where their nests are placed remains largely unanswered.

Life for a vulture takes place largely in the air, and it isn’t just their soaring abilities that help them out. Vultures have keen eyesight and, unusual among birds, a sharp sense of smell (they reportedly are particularly sensitive to the scent of certain chemicals produced by the onset of decay in animal flesh). A vulture goes shopping, then, in prolonged soaring flight with constant scrutiny of the land below for anything dead, or looking to become that way soon. These are patient birds, and if a potential meal isn’t quite holding still yet, a vulture will wait.

Turkey vultures were once rare in Massachusetts, occurring regularly in the state only over the last 50 years or so as their range gradually extended northward. They were slow to get established on the Vineyard, probably because, like many other soaring birds, they dislike flying across large bodies of water (which don’t tend to produce the warm updrafts that lift a soaring hawk or vulture). But once established here, they rapidly settled into year-round life on the Island; though most vultures at our latitude migrate south for the winter, ours, again probably deterred by the surrounding water, spend the winter here, and I’ve seen little indication of any vulture traffic at all between here and the mainland.

Birds, of course, evolve for survival and not to gratify the sensibilities of human beings. It’s not fair to blame these birds for their habits, and indeed, the removal of carrion can be considered a public service. You needn’t think too hard about the specifics of what vultures do, if you don’t want to. But keep an eye out for their graceful soaring and give these odd birds some respect for the remarkable ways they’ve evolved to do their job.