A Project Tracks Oystercatchers to Save Them
Wildlife biologists are on the trail of a much-beloved beach bird, trying to get a fix on where it spends the off-season.
One early morning last April, Lindsay Addison set off on a mission of deception. To prepare, she packed a decoy, a net, and a $3,000 miniature backpack.
Addison is a wildlife biologist studying a handsome red-billed shorebird called the American oystercatcher, found in coastal areas from Nova Scotia to Texas. Unfortunately, like most shorebirds, oystercatchers are vulnerable to habitat loss, human disturbance, and prowling predators, including raccoons, foxes, and feral cats. While quite a lot is known about how and where these birds spend summers and winters, where they rest and refuel in transit is somewhat mysterious. By tracking the birds' movements, researchers hope to identify the challenges that oystercatchers face throughout their lifecycles, in every season, and take steps to help protect them.
Thus Addison, 34, has become a de facto spy, working as a coastal biologist with Audubon North Carolina to deploy sophisticated satellite tracking devices on unsuspecting oystercatchers. Oystercatchers like Arnie, who spent this past summer on the tiny spit of sand called Ferry Slip Island in the middle of the Cape Fear River near Wilmington, North Carolina.
Navigating a 23-foot, flat-bottomed boat through giant wakes made by ocean-going container ships and tankers traveling the busy shipping channel, Addison charted a course toward Ferry Slip that April day. Ted Simons, a U.S. Geological Survey biologist and ecology professor at North Carolina State University, served as both co-captain and co-conspirator. Their target was a bird with a 2007 birth certificate in the form of an orange leg band it had received at its nest on New Jersey's Champagne Island. Such leg bands are commonly used as crude devices for tracking birds' movements. Arnie was about to get an upgrade.
The ruse was set. A recording of an oystercatcher territorial call played in the background and a carved wooden decoy sat strategically near a patch of nets designed for capturing birds safely. Just as planned, Arnie got all riled up, strutting about, prancing to and fro, calling, flying and running at the decoy--generally making it known that this Trojan bird wasn't welcome. "Once they hit their [tolerance] threshold, these birds go into a blind fit of rage," Simon said. "They can get into serious fights protecting their territories; they have sharp claws, and they can do some pretty serious karate kicks when they're attacking another bird." Before long the angry bird stepped into a net and was caught.
With Arnie in hand, Addison and Simons set about fitting the bird's new gear. The latest fashion in the world of high-end oystercatcher tracking devices consists of a solar-powered satellite transmitter equipped with a six-inch-long antenna and attached to the bird's body with a pair of Teflon-strap leg loops. The transmitter is smaller than a thumb and weighs about as much as two quarters. For a bird the size of an oystercatcher, the load is about the same as a 180-pound man carrying a five-pound sack.
As they saddled up Arnie, the researchers continuously checked to make sure his rig wasn't too snug but also that it was secure enough to stay put until spring. Then they watched quietly to see if Arnie could walk and behave unencumbered. Satisfied, they set Arnie free. The day's fieldwork was complete. "We did the capture, put the backpack on safely; the bird was healthy; and the transmitter was transmitting," said Addison. So far, so good.
In the following weeks they watched Arnie preening, feeding, walking around--and oftentimes just sitting there. Then Arnie became a parent, tackling the all-important job of feeding a chick and shading it from the harsh sun. When the tide went out, exposing oysters, clams, and mussels along the shore, Arnie and its mate rushed in to collect food for the chick, now known as CF4. Addison visited often to check on the family. "You get to see all the things they do. One comes in and opens a clam in front of its chick, and that's a big deal. It's fun."
But Addison wasn't smiling in July when she swung by Ferry Slip to see how things were going and found Arnie walking about sans transmitter. "He had managed to shuck his backpack and had gone back to being a free oystercatcher," she wrote on the tracking project's blog. "We were not totally surprised that this happened, but it is a setback, since we will not be able to monitor Arnie's movements remotely." The loss of a transmitter didn't mean, however, that Arnie wouldn't continue to be watched. "For as long as possible, we'll keep an eye on him, and then hope for additional sightings when he moves south, as we think he will."
Arnie was the first of six oystercatchers to receive transmitters. Two more have since "shucked" their packs. But the remaining birds' movements are providing scientific insights, as well as public education. In Wrightsville Beach, North Carolina, kids attending the local elementary school were given the chance to name one of the tagged oystercatchers. They called the bird Oreo, for it's classic black and white plumage.
All summer long they monitored Oreo, watching through binoculars as the bird and its mate incubated three eggs, and sharing information with visitors to explain why certain sections of the beach are designated for birds only. The kids were overjoyed when Oreo's eggs hatched on Memorial Day weekend. But for all the fanfare, Oreo soon became the "poster child for why it's so hard to be an oystercatcher," Addison said.
None of the chicks survived. The runt died early on, a common casualty among nestlings. The second chick disappeared overnight--probably killed by a predator. The third succumbed to a broken wing shortly after it fledged. "Oreo and his mate did everything right; they were good parents," Addison said. "It just takes one piece of bad luck to lose a chick. So the precariousness of their success is the takeaway. They have a hard enough time with all of the threats they face--tides, random bad luck like a broken wing, temperature stress, predators--and we add human disturbance."
At the end of summer, the number of birds carrying transmitters was half of what the researchers had aimed for. "We've got fewer birds," Addison said, "and we hope not to lose any more. But this is fieldwork; you're dealing with the elements, all of these things are out of our control. You do as much as you can, hope for the best, and see what happens. We're also learning how to do this better."
The project's online map of the oystercatchers' locations shows that some of the birds are moving. Mind you, oystercatchers are not marathon migrants like red knots, peregrine falcons, Swainson's hawks, or hummingbirds that can cover thousands of miles on a one-way trip. Oystercatchers banded in Massachusetts are sometimes sighted in southern Florida, more than 1,000 miles away. But some birds don't migrate at all. Others hopscotch along the coast. Still, the information that can be gathered by tracking them is as important as ever.
"In North Carolina oystercatchers are a species of special concern," Addison explained. "From Texas to Maine there are about 11,000." In recent years population numbers have begun to increase slowly but steadily, indicating that species protection and habitat management on the birds' breeding and wintering grounds have helped the population stabilize. The new tracking data will further pinpoint some of the places between the breeding and wintering grounds that are key to the oystercatcher's long-term survival. "What are the places that birds need to make a successful trip--whether it's a 200-mile journey, a 300-mile journey or a 3,000-mile journey? Knowing which areas they use as stopover sites tells you about their needs, and having that info is helpful to their conservation."
This week the birds still wearing tracking devices have been seen frequently roosting with other oystercatchers, something they didn't do in the territorial summer breeding season. One of them recently flew as far as South Carolina's central coast, and it seems to be hanging out there--at least for now--foraging in the mudflats with the other red-billed birds. During the next few months some roosts may grow to number in the hundreds, or more in some popular wintering sites. "We can have seen roosts of a couple thousand birds in Florida," Simons said. "When you're thinking about the entire population being 11,000 oystercatchers, that's significant. You may have 20 percent of the population in one spot."
In February, many of those birds should start heading back to their summer beaches and preparing to breed. With any luck, when they arrive in early March, the remaining three will still be wearing their designer backpacks.
Addison and Simons will be waiting, hoping to find them once again shucking oysters at the local raw bar.