In recent years, the birds didn't gain the weight they needed at their Delaware Bay stopover, and the departures were sporadic, uneventful.
But this year, in part because of good weather, the birds did gain weight, priming them for reproductive success. If they have ample young, it could bolster a population considered to be on the brink.
The bay is known worldwide for the springtime spectacle of dozens of shorebird species migrating through. All have declined, but none as much as the red knot.
The knots begin one of the longest migrations on the planet at the tip of South America. Every May, they stop at Delaware Bay, emaciated, to bulk up on the fat-rich eggs of horseshoe crabs, which are just then coming ashore to spawn.
The birds need to double their weight in about 10 days to make it to the Arctic in time to breed and get out before the late-summer snows.
Once numbering nearly 100,000 on the bay, the birds have declined to about 15,000. Biologists blame a reduction in the number of crabs, which were heavily harvested through the 1990s.
Gradually, in what officials said was the first time a species not in trouble was regulated to help another that was, crab harvest restrictions have been enacted.
Still, neither the crabs nor the birds have shown a comeback. Biologists fear the red knots could plummet into extinction with an event as simple as a summer snowstorm in the Arctic or an oil spill in South America.
Advocates have repeatedly, but unsuccessfully, tried to get the U.S. Fish and Wildlife Service to designate the bird - a subspecies called Calidris canutus rufa - as federally threatened or endangered.
Yesterday, the researchers packed up and headed home after spending a month on the bay capturing red knots with sophisticated netting devices. They logged biologic data and banded the birds before setting them free.
Australian shorebird expert Clive Minton, who has joined Niles on the bay since 1997, called it "an exciting year. We think we're really seeing the beginning of a possible turn-round in the fortunes of the crabs and the shorebirds."
Based on the birds the biologists netted, Niles estimated 60 percent reached their optimum weight before heading north. Last year, only about 15 percent did so.
What made the difference, the researchers said, was a surprising ally: the weather.
"It cooperated beautifully," said Amanda Dey, a biologist who is now the DEP's lead red knot researcher. With calm waters and warm temperatures, the crabs swarmed ashore to deposit their eggs in the soft, moist sand.
She said that for the first time in more than a decade, the researchers were even seeing "washes" of eggs on the beaches.
Biologist do not yet have a final red knot count for this year because clouds and fog hampered the weekly aerial surveys. Based on ground counts, however, Niles doubted the birds had increased.
If the birds do have record numbers of young in the Arctic this summer, the researchers are unlikely to know it for more than a year.
They base overall population estimates on the January count in Tierra del Fuego, and the first-year young do not fly that far south.
So any uptick in the population likely would not be documented until 2011.
Contact staff writer Sandy Bauers at 215-854-5147 or firstname.lastname@example.org.