Tracking the migration of the American oystercatcher – with tiny transmitters

CorrespondentSeptember 29, 2013 

When the migrating urge hit the American oystercatcher named CFX in mid-August, he took off from his Outer Banks home to join the party gathering on Capers Island, off Charleston.

There, up to 1,000 of his fellows, striking black-and-white shorebirds with long orange beaks and orange-ringed eyes, fly in from Texas to Maine to spend the winters.

A South Carolina Department of Natural Resources officer spotted CFX by the identifying number on the bright green leg band worn by North Carolina-banded birds, and notified North Carolina scientists who had been keeping an eye on him.

Audubon North Carolina coastal biologist Lindsay Addison and N.C. State biology professor Ted Simons already knew where he was, however, through a tiny backpack – a satellite tracking transmitter – CFX wears. They caught him last spring at his home in Cape Lookout National Seashore and attached the $3,000 device.

Powered by a solar battery, the 1-inch-by-1/2-inch backpacks that Addison and Simons have attached to six North Carolina oystercatchers inform orbiting research satellites every couple of days of the birds’ whereabouts.

Checking in via computer, the biologists knew not only that CFX had gone to Capers Island but also that he made a pit stop at Masonboro Island, near Wilmington, along the way.

They – and CFX’s many fans on the tracking project’s website, www.oystercatchertracking.org – didn’t know how the bird weathered the trip of more than 250 miles, however.

When S.C. DNR gave them the heads up, they told his fans via the constantly updated website that “CFX was looking healthy and preening himself while the flock waited for the tide to fall and their oyster buffet to become available again.”

‘Species of special concern’

Why all the fuss about a bird that lives only on the fringes of the Atlantic and Gulf coasts and measures 17 to 21 inches long? It numbers only about 11,000 in its entire range – about half what it was before massive hunting wreaked havoc in the late 1800s and early 1900s.

Closely observed oystercatchers, say those who study them, are in a perfect position to be the “canary in the coal mine”: an early warning system for threats to the coastal environment.

They eat oysters, crabs, mussels and marine worms, a diet dependent on clean, unpolluted estuaries.

They scrape out a nesting spot and lay their eggs right on the beach, often in front of dunes, where their eggs are in danger of overwash during storms and unusually high tides, a threat that scientists fear will grow with rising sea levels.

The eggs and chicks are at the mercy of beach-going humans and the unleashed dogs they bring with them, as well as raccoons and other creatures attracted by the presence of humans. The spotted eggs blend in with the sand – nature’s protective coloration – but people step on them and vehicles run over them.

As a result, North Carolina’s 300 to 400 nesting pairs have found refuge in government-protected national seashores or conservationist-supervised islands off the coast or the inland waterway. The state lists the American oystercatcher as “a species of special concern.”

For a safe migration

Banding has long shown scientists the endpoints on the birds’ migration journeys, but how they get there has been a mystery. Now, the four groups sponsoring satellite tracking – Audubon North Carolina, the National Fish and Wildlife Foundation, Together Green (Toyota/Audubon partnership), and N.C. State – hope to learn enough to help keep them safe and healthy en route.

They hope in the future to take advantage of GPS technology, which is being used to track bald eagles and other large birds. So far, those transmitters are too large to be carried by oystercatchers, which each weigh 1 to 1-1/2 pounds.

A side benefit, say the scientists, is that oystercatchers’ looks and temperament make them great “poster birds.”

“Not only are they beautiful, humorous and attractive, interesting birds with interesting behavior, their life histories tell a really good story about the coastal environments and the factors affecting them,” said N.C. State’s Simons.

Those orange-ringed eyes on a black head look continually surprised, and the heads bob up and down, orange beaks pointed downward, as a couple walk side-by-side during courtship. Their mating call is a sharp, rhythmic chirp called “piping.”

The sexes look alike, so Addison arbitrarily designated males and females – CFX may be a girl.

Both sit on the eggs and are attentive parents, often standing over eggs or chicks to shade them from the sun.

Threats to their territory bring out the swashbuckler in them. “They will put their heads down, put their feathers out, charge at each other and call,” Simons said.

“Making a big website out of it, putting the birds on Facebook (under Audubon North Carolina) and Twitter (under AMOYtracking) allows people to track the birds,” said Addison.

It also lets watchers in on the birds’ misfortunes. Because of predators and other factors, all six pairs were only able to raise one chick among them this summer. It belongs to Arnie, a Cape Fear River bird.

Oreo, named by Ann “Cissie” Brooks’ fifth-grade marine science students at Wrightsville Beach Elementary School, lost the last of her three chicks in front of onlookers at Wrightsville Beach, where she lived in a protected area.

A gull or another oystercatcher attacked so viciously that the chick had to be caught and euthanized.

Oreo’s many fans, said Addison, “were very sad.”

Nesting success for oystercatchers is very low, with only about one-third of nesting pairs’ fledging chicks in any one season, Simons said. But the birds live 20 to 25 years, and that success rate is enough to maintain a stable population.

And Simons said that North Carolina’s total population seems to be inching upward, thanks to the closing of certain areas of beach at critical times and efforts by the National Park Service and the public to better handle raccoon-attracting garbage at Cape Hatteras and Cape Lookout national seashores.

The satellite tracking attempt suffered a minor setback when three birds – Arnie, CF7 and Orange Green – preened underneath the transmitters’ Teflon leg bands so vigorously that the backpacks fell off and were lost.

The scientists had hoped that all six birds would keep the 3-ounce devices on through migration, but the information already gained made up for the disappointment, Addison said.

“It’s a learning process. We’re learning about their movements, their habitat use – and also about techniques for better attaching these transmitters.”

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