A Story About the Red-breasted Sandpiper

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Bound for Arctic, with a layover at Delaware Bay

Scientists trace shorebirds' migration from South America, hoping to find clues that can save a dying subspecies

By MOLLY MURRAY
The News Journal

Sometime between 1808 and 1812, naturalist Alexander Wilson visited Cape May, N.J., and spotted a bird he called the red-breasted sandpiper -- the bird we know today as the red knot.

He saw horseshoe crabs, too, calling them king crabs. But it was not for another 170 years that scientists had a full understanding of the global significance of Delaware Bay as a springtime staging area for red knots, which feed on horseshoe crab eggs, and a host of other migratory shorebirds.

In 1981 and 1982, a four-man team, led by Pete Dunne of the New Jersey Audubon's Cape May Bird Observatory, flew over the shores of Delaware Bay in May and early June.

"Our work revealed a staging area of remarkable proportions, one largely unknown to the scientific community and comprised mostly of red knots, sanderlings, semi-palmated sandpipers and ruddy turnstones," the men wrote in their report.

About the same time, world-renowned red knot researcher Brian Harrington asked Dunne where he could find a lot of red knots, Dunne said, "Define a lot."

"He said, '500,' " Dunne recalled. "I said, 'What about 50,000?' He said, 'You're joking.' He got it right away. He said this was the mother lode."

How long the birds have been massing here is one of the many mysteries of the horseshoe crab-shorebird food web dynamic that scientists are struggling to understand.

In some ways, they are in a race against time. There are international concerns, based on computer modeling, that the Delaware Bay subspecies of red knots -- Calidris canutus rufa -- could go extinct as early as next year -- the population is that depleted.

Among the other unknowns is the discovery that there likely are three distinct populations of red knots that migrate through the Delaware Bay region: one set of about 7,500 birds that spends the winter on Georgia's Altamaha Delta and Florida's Gulf Coast, sometimes traveling north along the South Carolina coast in search of food; another group of about 7,500 birds that spends the winter in Maranhao in northern Brazil; and a third group of about 18,000 red knots that spends the winter in Tierra del Fuego at the southern tip of South America.

Those southernmost birds travel an estimated 5,000 miles in the first leg of their spring migration.

Once in the Delaware Bay, they find the highest density of horseshoe crab eggs at Mispillion Harbor on the Delaware side of the bay.

But the favored nighttime resting area is in Stone Harbor, N.J. -- a round trip of about 58 miles from the Atlantic Coast of New Jersey to the western side of Delaware Bay.

The birds are closely linked to the horseshoe crab when they are here and many scientists believe that overharvesting of the crabs in the 1990s led to a dramatic drop in egg availability and a decline in red knot populations.

Dunne said there have been other dramatic declines in horseshoe crabs but the last one -- when the crabs were harvested as a fertilizer and feed for hogs -- would have likely coincided with market hunting for shorebirds. The birds were hunted as a food and for their feathers for the millinery trade.

This latest horseshoe crab harvest went to provide bait for conch and eel fisheries. New Jersey now bans the harvest of all horseshoe crabs. Delaware limits the harvest to 100,000 males after the peak of the shorebird migration.

Red knot populations, meanwhile, have fallen dramatically: In those 1981-82 flyovers, Dunne and his team estimated more than 150,000 red knots using Delaware Bay. In recent years, the Delaware Bay counts have totaled about 15,000 red knots.

Three feeding strategies

Long-distance flyers such as red knots go through a physiological change as they migrate north from Tierra del Fuego.

Their digestive system transforms and they become flying machines. When they arrive at Delaware Bay, they weigh about 110 grams, sometimes less.

Jean L. Woods, curator of birds at the Delaware Museum of Natural History, said the Tierra del Fuego birds may feed exclusively on horseshoe crabs simply because they are the easiest things for the birds to digest.

Scientists speculate that birds from Florida, Georgia and closer migration zones may have a more diverse feeding pattern simply because they have not gone through the rigors of such a long migration.

Once here, they have two to three weeks to put on weight -- the optimum is 180 to 220 grams.

Scientists estimate that each red knot needs 13,000 horseshoe crab eggs a day to maintain their weight and 24,000 eggs to fatten to the optimum.

They stop feeding in the days before they fly north and once again undergo physiological changes. The size of digestive organs reduces and they increase their flight muscle size. The birds, often leaving en masse, fly inland, north and west across the vast boreal forests of Canada and then over the low tundra and along the coast of James and Hudson bays -- almost 2,500 miles -- when they reach their Arctic breeding grounds.

Their digestive system is restored but often they live off their fat reserves -- packed on in Delaware Bay -- until the spring hatch of Arctic invertebrates erupts.

Key to survival

Nancy Douglass, a regional species conservation biologist with the Florida Fish and Wildlife Conservation Commission was sitting in her office one day when she got a call from Larry Niles, at the time a wildlife biologist and nongame and endangered species manager in New Jersey. Niles, now a private consultant, is an expert on red knots. He told Douglass he thought Florida may hold the key to red knots.

Douglass said she knew there were red knots in Florida but they hadn't attracted anyone's attention.

She took the story of the red knot to wildlife administrators in the state capital.

Folks were interested, but there wasn't any money. There are so many species in Florida that need attention -- the Florida panther, the manatee, the black bear, she said.

"I felt like I had failed," she said.

Douglass said Niles found some grant money and assembled an international team of researchers that came to Florida to study the red knots.

"Larry amassed an incredible team," she said. "I felt like I was in pretty tall cotton, as we say down South."

The team spent two years studying the Florida red knots and then Douglass was able to find grant money to do more research.

No place like Florida

The birds congregate on the Gulf Coast in the area around St. Petersburg and Sarasota. People are everywhere.

In South America, the settings are remote and austere. Along Delaware Bay, the beaches are among the least traveled.

"They're in a magnifying glass here for pressure," she said. "No place is like what they face in Florida. ... They definitely modify their behavior accordingly."

That leads to another unanswered question: Have the birds always been there, wintering under the radar screen?

In 1980, the spring edition of the Florida Field Naturalist noted "a rare gathering" of red knots on Casey Key, Fla. The seven-mile long barrier island is in Sarasota County.

"We observed large flocks of red knots along the Gulf beach as far as we could see in both directions. ... These were feeding flocks. ... We estimated the total number of knots for six miles of beach was in excess of 6,500. ... We find it difficult to assign a reason for a large concentration of red knots but our conjecture is it was storm related. If food related, probably other species of shorebirds would have been present."

The authors of the report went back and looked at Christmas bird counts back to 1973 and found far fewer red knots recorded. The previous high count had been in 1969, when 4,245 were counted in one day at St. Petersburg.

Mispillion Harbor

Scientists believe when the Florida red knots arrive at the Delaware Bay, they may be in better shape than their relatives from South America. No one is sure whether the Florida birds -- and those from northern Brazil -- are genetically different from the Tierra del Fuego birds. No one knows, at least not yet, if it is a subspecies of the subspecies rufa or a different species altogether. They do come to Delaware Bay. Scientists can tell from the color-coded leg bands.

Once here, so much depends on the availability of horseshoe crab eggs. While fisheries resource managers believe the population of crabs is stable, the question remains whether there is the density of eggs the birds need for optimum weight gain.

The one bright spot for horseshoe crab egg density is Mispillion Harbor, near Slaughter Beach.

The birds congregate here, feeding on the eggs. But resting is another matter.

Red knots had rested on the marshes west of Cedar Creek, but in 2004 and 2005, those marshes flooded and the birds could not roost there.

Kathryn Zimmerman, a graduate student working on a master's in conservation biology at the University of Michigan, will try to get answers using a small radio transmitter, about the size of a dime. The transmitter -- and several more like it -- will be placed on selected red knots this spring to see where they go to roost.

Historically, the birds like large, flat expanses for resting when they cannot feed and they flock together. But predators like red foxes can be a problem.

Zimmerman said researchers already know that many of the birds fly across the bay to a sand flat at Stone Harbor.

"Those locations are limited in Delaware," said Kevin Kalasz, a zoologist with Delaware's nongame and endangered species program who coordinates the red knot research efforts in Delaware.

Habitat could be another key. Once wildlife administrators learn what habitat works best for red knots, they could use the information to enhance areas where birds can roost.

David Carter, an environmental program manager with Delaware Coastal Programs, said in the 1980s there were more sand spits along the Delaware Coast at places like Port Mahon. But shoreline erosion has taken a toll and much of the habitat at Mispillion Harbor was manmade.

The jetties provide a low wave area for horseshoe crab spawning and the abundance of eggs attracts the shorebirds.

Carter said he worries that so many birds concentrate at Mispillion Harbor.

"They're putting all of their eggs in one basket," he said. "We recognize there is a big problem. ... It's like having nothing at all except having everything in high-growth, high-risk investments. So we need to protect that habitat."