EASTHAM — The sunburned scientists are crouching behind the sand-colored blind, one peering through a scope, another quietly issuing orders over a walkie-talkie, the third holding a detonator.
The team has been hiding on Nauset Beach for hours, peeking through the camouflage on a weeklong mission to catch their increasingly elusive prey: red knots.
The small shorebirds, which the federal government proposed on Friday to list as one of a few threatened species in the United States, sojourn on Cape Cod this time every year on their journey from the Canadian Arctic to Tierra del Fuego, among the longest annual migrations of any bird.
“Is that a knot that’s sitting?” says Stephanie Koch, a biologist at the Eastern Massachusetts National Wildlife Refuge Complex, squinting through the scope on this recent afternoon.
Ellison Orcutt, a Mass Audubon naturalist, picks up his binoculars to confirm it’s a knot, whose numbers have plummeted about 75 percent over recent decades. “There’s one in the center,” he says.
They’re waiting for the cinnamon-faced birds, which have 20-inch wingspans, mottled gray plumage, and dark, spearlike bills, to land on their long array of nets buried in the sand. When that happens, they will fire off a special cannon, sending projectiles that are attached to the net some 30 yards into the air. If all goes well, this allows them to capture a large number of birds without killing or injuring them.
They watch the knots as their small, clawed feet pad over the sand, as they dawdle in the warm sun and gaze at the seals lolling in the marsh, and then as they take flight, almost toying with the scientists.
“It’s just a lot of waiting right now,” Koch says.
The team’s leader, Larry Niles, a wildlife biologist with Conserve Wildlife Foundation of New Jersey, radios in from a few hundred feet across the beach, where he’s trying to “twinkle” the birds, or gently prod them toward the nets.
He’s convinced the birds are learning, that after several days of watching their comrades get trapped in the nets, they now know to avoid the grooves and ropes stretched across the sand.
“They’re going to be wary,” he tells his colleagues over the radio.
Financed by thousands of dollars from the Fish and Wildlife Service, the team is seeking to tag as many of the knots as they can, particularly the juveniles, which they hope to track as they make their first 9,300-mile passage to the tip of South America.
Listing the birds as threatened involves a bureaucratic process and comment period that takes a year before most of the consequences take effect. The designation, which initially comes in the form of a proposal and is a step below endangered, could mean beach closures on the Cape between July and October when the birds come to feed on clams and mussels. It could also mean additional federal money for research, providing assistance to other countries to help them stop hunting of the birds, and protecting the knots from predators by doing such things as moving platforms used by peregrine falcons farther away from where the birds congregate.
The rufa subspecies of red knots, which has been a candidate for protection under the Endangered Species Act since 2006, join polar bears and wolverines to be among the first animals to receive such a designation because of climate change. A threatened species – there are only 15 other birds similarly designated in the United States and only five such animals in Massachusetts — means that it’s “likely to become an endangered species within the foreseeable future,” according to Fish and Wildlife.
The bird’s population has declined sharply — the steepest drop-offs have been since 2000 — as its breeding grounds in the Arctic have warmed, feeding areas on Cape Cod and in Delaware Bay have been affected by higher sea levels and ocean acidification, and rising temperatures have interfered with their lifecycles, scientists say. The warming temperatures, for example, have caused horseshoe crabs in Delaware Bay to lay eggs earlier than usual, leaving the birds with less to feed on before their critical spring flight to the Arctic.
Their instinct is to“time it when the food is superabundant,” says Wendy Walsh, a senior biologist with Fish and Wildlife.
The scientists combing the beach for red knots did not wait for the government’s decision.
For the past three years, they have been coming to Cape Cod to attach geolocators to the birds’ spindly legs, a delicate, trying task that until this year has netted only 61 knots. So far this season, they have caught just another six.
For their effort to be worth it, they will have to recapture the same birds and download the data, which they hope will tell them where the birds stop and for how long. They will then do their best to protect those areas.
On Nauset Beach, where they have posted signs that read “Shorebirds Need Our Help: If birds appear nervous or take flight, you are too close,” the challenges to their work are obvious. There are people driving trucks near resting knots, boaters anchoring in areas where they wade, and curious passersby scaring them away.
Niles radios one of his colleagues to divert the truck and sends another to ward off a boat that just motored up to the beach.
The scientists have been at it since early in the morning, and now it’s afternoon, with the tides rolling out.
“We’re never going to catch them now,” Niles said.
Koch shakes her head. “There’s no shot,” she says.
Then they get a call from one of their scouts.
The binoculars and scopes emerge from behind the blind. They scan the beach for the birds, which appear to be mingling with seagulls.
Then they fly away.
“And there they go,” Koch says.
“I love this work,” she says, “but it can be very frustrating.”
Niles has witnessed the decline of the red knots over the two decades he has sought to protect the birds. It will become more challenging to track them as numbers diminish, he says.
He checks in with his scouts, consults his colleagues in the blind, and decides it’s time.
Without any birds to show for the day, he gives the order to pack up.
“We have a lot of work left to do,” he says.