"For the first time in many years, I feel like there's hope," said Darin Schroeder, vice president for conservation advocacy with the nonprofit American Bird Conservancy.
Since the 1990s, red knots declined from about 100,000 on the bay to fewer than 25,000. Biologists blame the commercial harvest of their main food source, horseshoe crabs. Inedible by humans, the crabs are used as bait for other species.
Most of the birds winter along a small bay in the Tierra del Fuego area of Chile. That population also has suffered severe declines - from 50,000 to about 10,000, said Larry Niles, a biologist with the Conserve Wildlife Foundation of New Jersey, who has studied the red knot for more than a decade.
The threatened-species designation could lead to restoration of beaches where crabs lay eggs and the birds feed, experts say. It could also prompt programs to keep humans off bay beaches for the few weeks in May when the birds are there.
Changes to the crab harvest are another option. New Jersey has a moratorium, but Delaware has a limited harvest.
Conservation groups want a closer look at the biomedical industry, which bleeds horseshoe crabs for a key component of their blood. It is unclear how many ultimately die.
Protections for the red knot also would help other shorebirds, advocates say. The red knot may be "at the tip of the spear," said Eric Stiles, president of New Jersey Audubon, but numerous other shorebirds along the Atlantic are declining, often due to loss of coastal habitats.
A species listed as "threatened" is likely to be in danger of extinction in the foreseeable future. An "endangered" species is in worse shape - in immediate danger of extinction.
The red knot was added to a "candidate" list in 2006. But the bird's supporters said the list was little more than a never-ending holding pattern where species go to die.
At that point, President George W. Bush had stripped funding from the Fish and Wildlife Service, and conservationists believed suing was the only way to get a species listed. Conversely, service staff was so tied up with litigation, it could do little else.
In 2011, a federal judge approved a settlement for two groups that had sued, and set up a schedule through 2017 for the service to make determinations on 750-plus species.
By now, more than 100 have been listed, and about 40 more, including the red knot, have been proposed, said Noah Greenwald, endangered species director at the Center for Biological Diversity, one of the litigants.
"We're happy that these species that desperately need protection are finally getting it," he said.
But many still aren't happy with the listing process - not Washington's or Pennsylvania's.
In 2011, when the court settlement was reached, Congress defeated a measure to prohibit further additions to the federal lists of threatened or endangered species. Additional proposals to limit lawsuits have not passed.
Pennsylvania legislators are considering bills that supporters say would streamline the state's listing process. They would require all listed species to be reevaluated within two years or dropped from the list.
"We are simply asking for sufficient burden of proof that a species is truly endangered or under a threat of extinction," said the chief sponsor, Rep. Jeff Pyle, a Republican representing Armstrong and Indiana Counties.
Environmental, nature, game, and fisheries groups and officials contend the bill is unwieldy and would lessen protections.
New listings would have to be approved by an independent review commission, which could take two or three years.
"In that time," said Thomas Au, conservation chairman of the Sierra Club's Pennsylvania chapter, "the species can already be extinguished."