This is the second part of a series on the shorebirds that make one of the longest annual migrations in the world, the 9,000-mile flight that spans the entire Americas, from feeding grounds on Tierra del Fuego to breeding grounds in the Arctic. The heroic journey has evolved over countless generations. But can the migration, and the red knot, survive the human-caused disturbance at a critical waystation on the U.S. Atlantic coast?
By Stuart Pimm
Delaware Bay, New Jersey–Stretching along the shore are perhaps thousands of shorebirds–dunlins, sanderlings, knots, least and semipalmated sandpipers, turnstones, and a few other species. They are all feeding with a particular intensity–as if they haven’t eaten for days and as if their very lives depend on it. Both are true.
This is one of the most spectacular wildlife spectacles in North America. Each year tens of thousands of migrant shorebirds cram into Delaware Bay to feed on the vast numbers of horseshoe crab eggs that have been laid in the mud.
Photos of shorebirds by Stuart L. Pimm
The knots have come from Tierra del Fuego, the very southern tip of the Americas. They will feed frenetically for up to ten days, put on a lot of weight, then fly to their breeding grounds mostly north of the Arctic Circle in Canada. Some go to the Queen Elizabeth Islands, above 75 degrees latitiude north.
But there’s a problem. There ought to be not thousands, but tens of thousands of knots in front of me. As amateur scientists count the knots along the various shorelines, the totals of a twenty, perhaps thirty, thousand knot are a huge cause for alarm. In the recent past, there were more than a hundred thousand knot.
Simply, a bird that spends most of its life in remote places, as far from people as one can get, has declined precipitously because of what’s happening to its key refuelling stop.
Banding shorebirds video by Stuart L. Pimm
Knots occur in Europe and Asia and undertake similar, extraordinary migrations. There’s also a West Coast knot. But the American red knot is distinct. Yet were it to go extinct, it would not be the first.
Over a century ago, Eskimo curlews were abundant enough to be on the menu of New York restaurants. They did breed in remote parts of Canada and wintered in South America. No one is sure quite sure why this curlew is now extinct. Like the American knots, they likely concentrated at important “truck stops” to feed up for long journeys. The last was seen in the 1980s.
In Eurasia, the bizarre spoon-billed sandpiper is critically endangered. Industrialization of estuaries in China, Japan, and South Korea threatens it–and many more familiar species, too.
New Jersey gets a bad rap. Parts of it are indeed industrialized and unappealing. But this part of the Delaware shoreline is lovely and the countryside is gentle, rural farmland with pretty small towns and frequent patches of forest.
Red knot migration map by NGM Maps
So what is wrong?
The birds are here to gorge on horseshoe crab eggs, get fat quickly, and fly thousands of kilometers to their breeding grounds, nonstop. They need a lot of energy and the eggs provide it.
Horseshoe crabs had been traditionally harvested for eel and minnow bait. The catch was low. In 1993 collapsing fisheries in New England led commercial fisherman to exploit conch–and the crabs were the preferred bait. They were collected, from the shore, quite literally by the truckload. Millions were harvested from 1996 to 2000.
Photo of horseshoe crab by Stuart L. Pimm
The numbers of the crabs tumbled to a tenth of their former numbers–and perhaps a hundredth of that in some years from 2002 onward.
The effect on the knots was disastrous. Banding knots–as I did last week (Ringing the knot on the New Jersey shore)–one can feel how fat or thin the birds are. Some are little butterballs and have likely been feeding for several days on the fat-rich eggs. Others are very skinny and perhaps have only just arrived.
In 2003, even by late May when the birds must depart, almost all the birds were skinny. The consequences on flying on an empty stomach? The mortality of the birds increased dramatically and their numbers crashed.
How do we know all this? As explained in the accompanying piece, this work–led by Larry Niles, his wife Amanda Dey, and others–is the result of a remarkable amateur-led effort to catch shorebirds around the world.
Photo of shorebirds by Stuart L. Pimm
I joined one team to catch knot, band, and weigh them. In addition to metal bands, each bird gets a colored leg flag. Dozens of volunteers scan the shoreline with telescopes looking for birds with flags. Each flag’s color tells where it was banded–here, or in South America, or the Arctic. And individual letters identify each bird uniquely.
The effort volunteers put in is quite extraordinary. More than 70 percent of the flags are seen again, allowing precise statistical estimates of how well the birds survive. Such observations, however, only help where there are people to make them.
So the team put 150 data loggers on the birds last year. These keep track of where the birds are each day by recording sunrise and sunset. One has to recover these loggers to access the data–and, so far this year, the team has got just one back.
Photo of red knot with a logger attached to its leg by Joanna Burger
Will the knot survive? Clearly not, if there’s an excessive harvest of horseshoe crabs.
We also need to know whether there are other places where human actions might be harming the bird.
With another week of fieldwork, there are more chances to recover the loggers. I’ll let you know how the season goes when it’s over!
Professor Stuart L. Pimm is a conservation biologist at Duke University, North Carolina. A former member of the National Geographic Committee for Research and Exploration, Pimm is the author of dozens of books and research papers, including the book “The World According to Pimm: A Scientist Audits the Earth.”