The groups sent a letter asking that two subspecies of Red Knot be listed under the Endangered Species Act.
An attorney for Washington D.C.-based Defenders of Wildlife says it's clear that the Red Knot faces imminent extinction.
The medium-sized shorebirds flock to the Delaware Bay each spring after flying nonstop from South America. They feast on horseshoe crab eggs to nearly double their body weight in less than two weeks before flying to their breeding grounds in the Arctic.
Environmentalists say harvesting of horseshoe crabs for bait is threatening the birds' survival.
