Jan/Feb 2010For Wildlife Watchers: American Oystercatcher by Rob Simbeck, photography by Michael Foster
Reproduction is a tricky business. In a world where survival itself is often hard-won and short-term, simply producing and raising the next generation can be seen as nothing short of miraculous.
Sometimes, as in the case of birds, the challenges are obvious. Wind and rain can dislodge or inundate nests. Plenty of animals eat eggs or hatchlings. A disruption in the food supply can preclude nesting success, as can hatching that occurs early or late, when food is not yet available or has become scarce. Throw parasites and disease into the mix and add plain old competition for finite resources, and it's no surprise that many species are doing well just to replace their populations.
The American oystercatcher is among those that may not be accomplishing even that.
"I'm definitely concerned for them," says Felicia Sanders, a wildlife biologist with the S.C. Department of Natural Resources who has studied these birds extensively. Her overriding concern, though, runs largely to the loss of habitat.
"Oystercatchers are strictly coastal," she says, "and there is more and more coastal development and use."
In South Carolina, oystercatchers have responded to the crowding of their classic nesting habitat - open beaches - in part by using the Atlantic Intracoastal Waterway, a navigational channel for commercial and recreational boat traffic that bypasses the possible hazards of open sea travel. Wakes from that traffic help create shell mounds in the waterway that mimic those created naturally by waves in bays and inlets. Oystercatchers use them for both roosting and nesting, although "nest" in this case describes little more than a scrape where the female will lay two to four eggs, which both adults incubate for about four weeks.
The trouble is that such sites along the waterway are as vulnerable as they are attractive. As nesting begins, the northward migration of recreational boats is under way, and their wakes, especially at high tide, often wash eggs away.
American oystercatcher - Haematopus palliatus
Description: Black head, brown back, white underside, long pink legs, long red-orange bill. 17 to 21 inches long, 18 to 21 ounces.
Range and Habitat: Coastal. Eastern race breeds from New England to the Gulf Coast.
Reproduction: April to June. Female lays 2 to 4 eggs in a scrape on a beach or shell rake.
Viewing Tips: Cape Romain National Wildlife Refuge, with a large wintering population, is a particularly good place to see oystercatchers. Watch from a distance, particularly during breeding season.
Nesting success rates are very low, according to studies undertaken by Sanders and her colleagues, including Janet Thibault, a Clemson graduate student. They suggest that for every four nests, just one bird makes it to fledging. They also indicate that oystercatchers have greater nest success at Bulls Bay, within the Cape Romain National Wildlife Refuge, than they do in nearby stretches of the waterway, although nest failure rate for the entire study was 85 percent. Boat wakes, predators - including other birds - and the nearness of food supplies all seem to be factors.
South Carolina and its nests are of particular importance because the state is a key portion of the species' range. More than four hundred pairs nest here, and more than a third of the 10,000 Atlantic and Gulf oystercatchers in existence winter here.
"Nests are pretty rare on beaches that have houses or a lot of disturbances," says Sanders, "and the disturbances are only going to increase."
These are striking birds - "charismatic" is the word Sanders uses. With their black heads, dark brown backs and wings with white patches, and white breasts and abdomens, they are memorable in flight. They can usually be seen working the beaches and bays on long, pinkish legs, eating the oysters that gave them their name as well as mussels and other bivalves. They use their long, red bills, flattened and shaped like oyster knives, to open them, clip the muscles that hold the shells together, and eat the oyster. While nesting, they will often pull mussels from the rocks to which they're anchored and take them back to the nest to feed their young. In fact, those young rely on their parents for food far more than most other shorebirds.
"It takes a long time to teach their young the technique," says Sanders. "Many other shorebirds can forage not long after they hatch. Oystercatchers bring oyster meat to the nest site and then as the chicks get older they follow them and learn." That process can take months.
Oystercatchers are monogamous and are loyal to nesting sites. They exhibit territorial defense in which "they work as a pair and will run along the beach or shell rake, running in unison and bobbing their heads, defending the site from intrusion by other pairs. It's very interesting - comical, actually," adds Sanders.
Historically, the range of American oystercatchers stretched at least to the Canadian border. Indiscriminate hunting wiped them out as far south as Virginia until the Migratory Bird Treaty Act stopped the slaughter in 1918. Since then, their breeding range has extended northward into Nova Scotia again. A century ago they commonly nested on Sullivan's Island, Isle of Palms, Dewees Island and Capers Island just north of Charleston. Those islands now support virtually no oystercatcher nesting. Even in the past ten years, small numbers that nested on places such as Litchfield Beach and Pawleys Island have disappeared. Today, the Cape Romain region provides particularly good habitat and is well populated with oystercatchers.
Sanders and her colleagues are working to turn their knowledge into protection that will give these vulnerable birds a better chance at reproductive success. It's critical for wildlife watchers to give plenty of breathing room to these and so many other creatures that do not deal well with human interaction, or with the pets that can wreak havoc on nest sites. It's one of those cases where a watcher's appreciation is best demonstrated at a distance.