Female crabs take ten years or more to mature, so the offspring of the first crabs spared after 1998 are only now ready to mate. Their presence might help explain the spectacular spawning this year.
Red knots—which can live ten years or longer—are also relatively slow to breed: though the 6-week-old chicks will flutter south after the brief Arctic summer, they won't be ready to migrate north and mate for two years.
There are also myriad dangers outside the bay area, which, after all, is just a tiny portion of the territory these birds cover. The knots are vulnerable to oil spills, late snowmelts in the Arctic and even lemming population trends; if the lemmings die off, northern predators devour shorebird chicks instead. "If everything's great in Delaware, something awful can happen in the Arctic," Clark said. But all these potential stresses make a reliable food supply at their main rest stop even more vital.
As tagging wrapped up, several military helicopters swooped low over the harbor. The birders wondered if the choppers were carrying dignitaries, maybe even the president, to Washington from nearby Dover Air Force base. This possibility did not diminish their outrage at the disturbance. Hundreds of birds that had resumed pecking nearby took off, making a soft rushing sound with their flickering wings, like wind through marsh grass.
They never came back. Or so it seemed. Few shorebirds resumed feeding on the point that morning, and later in the day volunteers checked all the usual beaches: no knots. Nor were birds sighted the next day, save a handful of portly stragglers. Unbeknownst to the birders, flocks had likely begun leaving the evening before the tagging, steadily flowing out of the region. This was a day and a half ahead of schedule: they had plumped up quickly.
It could be that the birds fared well simply because there were more horseshoe crab eggs to go around. Other shorebird populations have declined in recent years as well, freeing up even more eggs.
"We're not sure exactly why things went well this year," said Larry Niles, a biologist with the Conserve Wildlife Foundation of New Jersey. "Crab populations don't change that fast and neither do shorebirds." Still, he added, "it was really gratifying to watch the birds go off in good condition." And for days after the knots departed, crabs continued to crowd the shallows, waiting for the tide to change.
Abigail Tucker is the magazine's staff writer. Doug Gritzmacher is a wildlife photographer and videographer.
CORRECTION: A photo in the October issue of Smithsonian magazine showed a sandpiper taking flight. The bird was incorrectly identified as a red knot; it was in fact a short-billed dowitcher. The photo has been removed from the photo gallery to avoid further confusion.