Scientists try to get a grip on one of America’s least-abundant and most colorful shorebirds
By Paul Tolmé
Hiding behind rocks on the Oregon coast, I peek up to watch an avian circus unfold 100 feet away. About 20 black oystercatchers—crow-sized birds with long red bills, pink legs and bulging yellow eyes—are feeding at water’s edge. They peep and pip loudly, raising a ruckus that sounds like someone squeezing a bathtub-full of rubber ducks. With their animated looks and behaviors, black oystercatchers are cartoon birds come to life.
No wonder they are a favorite of birdwatchers and researchers alike. “I find everything about them charismatic and compelling. They’re so goofy,” says Sue Thomas, a U.S. Fish and Wildlife Service shorebird biologist. “They’re the Mister Potato Head of birds.”
I have come to Oregon with Matthew Johnson, a wildlife ecologist with the U.S. Geological Survey who is launching a radio-tracking study of black oystercatchers. Johnson plans to strap thumb-sized transmitters onto about 20 oystercatchers so he can learn where they travel after nesting season.
About 10,000 black oystercatchers inhabit the Pacific Coast from Alaska to Baja, Mexico, making them one of the least-abundant North American shorebirds. While not endangered, they are a species of concern in the U.S. Shorebird Conservation Plan. “We want to get a grip on their movements so we can study those areas,” Johnson says. “To protect them we have to know where they are going.”
But first he must catch one.
Johnson’s trap—two wooden oystercatcher decoys and a speaker playing the bird’s calls—sits on seaweed-covered rocks about 20 feet from the pounding surf near Depoe Bay. Johnson hopes a few of the birds will waddle over to greet the decoys and become ensnared in a noose mat—wire mesh covered with tiny leg snares made of fishing line. This is our second attempt of the day. An earlier effort near Yachats was foiled by tourists who continually strolled by, frightening the birds.
Through binoculars from our hiding place, we watch as oystercatchers spot the decoys and land, peep, peep, peeping in response to Johnson’s recording. Suddenly, a wind gust topples the speaker and swamps the digital player in seawater, breaking it. Day over. Johnson packs up and heads home to get another digital player, hoping for better luck tomorrow. Oystercatchers are a tough catch.
Black oystercatchers feed in the sliver of rocky coastline between high and low tides, where they eat mussels, limpets, barnacles and snails. They nest on rock-strewn beaches, headlands, islands and sea stacks, where females lay two to three mottled gray eggs from April to June. Parents share incubating duties, and mates remain together through many seasons. “It’s almost romantic,” Johnson says.
Docile most times of year, oystercatchers become aggressive when nesting—flying straight at intruders, calling loudly and flashing that big bill like a cruise missile. “It definitely gets your attention,” says Julie Morse, who was strafed while studying oystercatcher nests as a University of Alaska-Fairbanks graduate student.
Recent studies in Alaska, home to more than half of all black oystercatchers, have yielded new insights into the birds’ nesting behavior and reproductive success. Solar-powered video cameras placed in Prince William Sound during the 2005 and 2006 nesting season recorded never-before-seen images. In one sequence captured by infrared lens at night, a wolverine raids a nest and eats the eggs. “That is so rare to see,” says Oregon State University graduate student Caleb Spiegel, who also collected footage of a pine marten, several minks and a black bear gobbling eggs. Predation is a leading cause of nest failures.
High tides are another hazard. Oystercatchers try to nest above the high-water line but sometimes miscalculate—with disastrous results. Spiegel captured footage of a parent struggling to save its eggs at night from a tidal surge, only to have the eggs swept away by a subsequent swell. Tidal flooding is a leading cause of nest failures in Prince William Sound, Kenai Fjords and Glacier Bay, where much of the oystercatcher habitat consists of sloping gravel beaches. Flooding is not a problem in the southern portions of oystercatcher range, where they nest on rocky islets and outcrops above the waves.
Humans are also problematic. Biologist David Tessler of the Alaska Department of Game and Fish is studying whether the wakes from cruise ships, tankers, ferries and other watercraft swamp nests in Prince William Sound. “These birds are already at risk of having their nests flooded at high tides, so any event that raises the water level might be an additional threat to local productivity,” says Tessler, lead author of the black oystercatcher conservation plan.
Another irritant: Kayak campers who pitch tents on rocky beaches near nests. Morse conducted an experiment in Kenai Fjords National Park to determine the effect of kayak campers on nesting. She and colleagues simulated the actions of campers and learned that oystercatchers incubated 39 percent less when disturbed.
Rising sea level due to global warming is also problematic, because it could shrink or eliminate some gravel beaches. “Whether or not sea level rise is a serious conservation issue depends on how rapid the change is,” Tessler says. In addition, ocean acidification due to increasing atmospheric carbon dioxide could threaten one of the oystercatcher’s favorite foods: mussels. A study of mussel beds on an island off the Washington coast showed about 15 percent of the bivalves disappeared over eight years.
Nesting oystercatchers face tough odds. Of 500 eggs monitored by Morse from 2001 to 2005, only 51 chicks survived to fledging age. Parents feed chicks for five weeks after hatching. Chick survival is higher on offshore rocks and islands where predators are few, but this habitat is limited. Unlike many shorebirds that nest in colonies, oystercatchers like privacy, nesting a quarter-mile apart—further limiting available habitat.
Juveniles follow their parents for much of the first year, learning to forage for mussels at low tide when the mollusks’ shells are slightly agape. “They jab their bill in and sever the connective muscle inside, then twist and pull the meat out,” says U.S. Fish and Wildlife Service biologist Gary Falxa, who studied oystercatcher foraging on the California coast as a graduate student.
One of 11 oystercatcher species worldwide, black oystercatchers are closely related to American oystercatchers of the Atlantic coast. The species overlap in Baja and sometimes interbreed, though unsuccessfully, scientists believe. Adult oystercatchers are long-lived, surviving 11 years or more. It’s easy to see why. After breeding season, the birds coalesce into flocks that flee at the slightest provocation, flapping from one rock outcropping to the next until the coast is clear. Precisely where they travel after breeding season remains a mystery.
In 2007, an international team of researchers conducted a study in Alaska and British Columbia to find answers. Their research provides a first glimpse of black oystercatchers’ migrations. The scientists trapped nesting oystercatchers on Alaska’s Kodiak and Middleton islands (the densest breeding area in the world), Prince William Sound, Juneau and on British Columbia’s Vancouver Island. The researchers outfitted birds with satellite and radio transmitters and Johnson tracked their travels.
Some of the birds over-wintered near nesting areas, while others migrated south to British Columbia, hugging the coast rather than flying over open water. Based on his tracking data, Johnson flew the British Columbia coast north of Vancouver Island in December, 2007, hoping to locate core wintering areas with thousands of birds. Instead, he counted fewer than 400. “That was a surprise,” says Michael Goldstein, a U.S. Forest Service ecologist participating in the study. “We still don’t know where the bulk of them are over-wintering.” Adds Johnson: “It’s hard to survey for black birds on black rocks that are widely dispersed.”
Determining where oystercatchers spend winter is important: “If there are large staging areas where they congregate, and that area is inundated by oil or some other chemical spill—that could have big repercussions on their survival,” Goldstein says. This is especially important in light of the push by some politicians and energy companies to increase offshore drilling. “Understanding where those areas are could enable us to implement policies to protect against some kind of human-induced disaster.”
Such a disaster struck on March 24, 1989, when the Exxon Valdez ran aground in Prince William Sound and spilled 10.8 million gallons of crude oil. An estimated 20 to 30 oystercatchers died as a result. The death toll was low because the spill hit before nesting season and oystercatchers that returned in April likely fled the intense cleanup. “They probably came back and thought, ‘Holy cow, look at this mess,’ and left,” says Brad Andres, national coordinator of the U.S. Shorebird Conservation Plan.
Andres studied the effect of Exxon Valdez on oystercatchers as a graduate student from 1991 to 1993. He discovered that chicks fed from oil-polluted mussel beds grew slower and had hydrocarbons in their feces. “The chicks couldn’t metabolize the food as effectively. They were stunted.” Parents compensated by gathering more food and increasing the runty chicks’ caloric intake. But overall, oystercatchers fared better than other bird species. “They walk on the beach and rocks, so they didn’t get covered in oil like ducks that landed in the oily water,” Andres says.
Oystercatchers might not be so lucky next time. “A spill off of British Columbia at the wrong time could whack a large chunk of the world’s population,” Johnson says.
We reconvene the next morning on the Oregon coast, and Johnson has a backup digital player in case of another mishap. He sets up his decoys closer to water’s edge, where oystercatchers feel safest. He turns on the speakers and we scurry to our hiding places, careful not to slip on the slimy rocks. Let the games begin.
Several black oystercatchers land nearby, and the flock steadily grows in size and verbosity. Our hopes rise when a bird walks to within 10 feet of the trap and stares at the decoys, then waddles away. “They don’t seem interested in the decoys,” says Johnson. “They aren’t juiced up on hormones like during breeding season.”
After several hours with no luck, Johnson realizes he must revamp his trapping method. Johnson’s study will expand to Washington and California in future years. Meantime, the U.S. Fish and Wildlife Service will conduct volunteer oystercatcher surveys as it has done since 2005 in Oregon. There are only about 350 of the birds on the entire Oregon coast. “They don’t have a lot of habitat options,” Johnson says. “They don’t like sandy beaches, so that rules out most of the coastline.”
Such research will have value beyond simply telling researchers whether oystercatcher numbers are rising or falling. It will also provide clues about the health of the Pacific’s rocky coasts, and perhaps strategies for how we can protect these unusual shorebirds and other coastal denizens. “There are only about 10,000 black oystercatchers on the planet,” Andres says. “That’s it. There aren’t 100,000 of them. It’s not a lot of birds. We ought to learn more about them so that we don’t wipe out a big chunk of them inadvertently.”
Paul Tolmé frequently spots black oystercatchers on the rocky beaches near his home on the northern California coast. His work can be seen at paultolme.com.