American oystercatchers have an interesting history on the East Coast. Originally, they probably occurred across much of the region, from the Gulf of Mexico possibly as far north as Maine, where John James Audubon reported them. But by the 19th century, their range had been dramatically reduced, probably the result of intensive gunning. Arthur Cleveland Bent’s account of the species, published in 1927, describes the bird as limited to the shores of the Gulf Coast and the deep Southeast. (He also describes the species as incredibly wary, very likely a behavioral trait resulting from decades of human persecution.)
With increasing regulation of shorebird hunting in the 20th century, oystercatchers began to march steadily northward, and climate change appears to be hastening the process. Considered a rare vagrant in the Bay State for much of the past century, oystercatchers first nested in the state in 1969 (on Chappaquiddick, as it happens). I first saw the species in Massachusetts around 1992, in Chatham, by which time it was established here as a breeder, but by no means common. At present, it is easy to find on most of the Massachusetts coast, with numbers gradually thinning out through Maine into the southern part of Nova Scotia. At a rough guess, perhaps 50 pairs nest on the Vineyard.
With the northward extension (or re-establishment?) of its range, the oystercatcher has changed its habits. The relict, Southern population familiar to Bent and his contemporaries was nonmigratory, engaging only in short-distance seasonal movements in search of resources. But today’s northern birds migrate rather strongly; there have been observations of birds banded on Nantucket as far south as Florida in the winter. Our breeders begin arriving in early spring, typically in March (but this year saw a stunningly early arrival in February); after the breeding season, the species filters southward, with only a few stragglers left by late autumn.
Even beginning birders will have no trouble at all identifying an oystercatcher. With a dark brown back, black “hood,” white underparts, these birds usually stand out well on the pale sand of our beaches. And oystercatchers possess one of the best beaks in bird-dom: a spectacular, dagger-like orange structure that is unmistakable.
The name of this species comes from a habit, reported by early observers, of using that bill like a shucking knife, to cut the tendon that holds shut the shells of bivalves like oysters. This behavior may be more evident in the South, where oyster reefs that are dry at high tide are prevalent, and might offer feeding habitat for these birds. At the Vineyard’s latitude, oystercatchers forage mainly along the wrack line and the waterline, sometimes picking small prey off the sand, sometimes probing deeply to capture worms or small mollusks. I suspect their diet is highly varied, consisting of a wide range of coastal invertebrates.
The food supply, in any event, must be plentiful for most of the season, since these husky shorebirds spend relatively little of their time feeding. A bird that is incubating eggs may sit on a nest for hours at a time (this species seems to swap off incubation duties much less frequently than do the much smaller piping plovers). And at other times, oystercatchers spend a good deal of the day just loafing, sometimes alone, often with a mate or other colleague. Pairs are quite territorial once they start breeding, but nests are sometimes quite close together, and I often see birds from different pairs lounging companionably at the waterline.
The relaxed demeanor of the species, though, changes when a threat is spotted. When disturbed, these birds often launch into air defense mode, circling the provocation and giving deafening “Wheep, wheep, wheep!” alarm calls. Crows near a nest, people walking past, or birds of prey are among the things that trigger these displays. But the thing that really seems to get an oystercatcher’s dander up, oddly, appears to be a turkey vulture. Why these benign scavengers are so hated is beyond me; perhaps they truly do threaten eggs or chicks. But if one flies near a nest, it is strafed and harried by shrieking, outraged oystercatchers until it is out of sight.
A long-lived species, oystercatchers often return to the same area to nest year after year. One bird I’m familiar with was banded as a chick on Nantucket about six years ago, spent a few summers relaxing in remote areas on Cape Poge, and then, as is pretty typical for the species, began breeding last year around the age of 5. A pair generally lays two or three eggs in a simple scrape in sand or fine shingle, and will renest, sometimes repeatedly, if the eggs are lost to predation or overwash. Occasionally one male will mate with two females, either producing two nests, or a single one stocked with as many as a half-dozen eggs.
It’s rare for all those chicks to fledge, much less reach maturity. But over the years that adult oystercatchers reproduce, the odds are good that they can produce more young than are needed to replace the adults, and this fecundity is undoubtedly fueling the northward march of the breeding range of this bird. So this species is a conservation success story: a bird once persecuted into rarity, but now a familiar sight along our entire East Coast.