Calidris canutus rufa

Red Knot rufa that was banded, measured and released on May 30, 2008 at Moores Beach, NJ
Photo by Faith Zerbe, Delaware Riverkeeper Network

At a Glance The red knot makes one of the longest yearly migrations of any bird, traveling on average 9,300 miles from its Arctic breeding grounds to southern South America. Range: Winter in Florida, Georgia, South Carolina and Texas, as well as Argentina, Brazil and Chile. Critical stopover during Spring migration along Delaware Bay.  Summer in Canadian Arctic. Fall migration utilizes coasts from New Jersey to Maine. Habitat Type: Coastal shoreline Primary Diet: Horseshoe crab eggs, while in Delaware Bay. Diet elsewhere includes bi-valves and invertebrates. Estimated Population: Less than 18,500 States with Current Habitat

Nominating Organization   Delaware Riverkeeper Network , American Bird Conservancy , American Littoral Society, Defenders of Wildlife , Delaware Audubon, Delaware Nature Society , Delmarva Ornithological Society, New Jersey Audubon Society

The rufa population of Red Knots relies on horseshoe crab eggs in Delaware Bay during the spring migration north.  There, in two to three weeks, the rufas must increase their weight by 50 to 100 percent by feeding on as many as 24,000 eggs a day.  This weight gain is vital to their ability to finish the migration to the Canadian Arctic and successfully breed. However, the overharvesting of horseshoe crabs for the commercial bait industry has diminished this vital food supply for the Red Knot and other shorebirds that rely on crab eggs.  Additional threats to the Red Knot includes habitat loss due to development in wintering areas and possibly global warming impacts to its arctic breeding grounds, but scientific studies clearly show that their weight gain during their migration in and around the Delaware Bay is the key factor to their success or failure.

Why Protection is Needed

Since 1985, there has been a 75% decline in the rufa Red Knot population. Between 100,000 and 150,000 Red Knot rufa used to stop along Delaware Bay each year during their migration north.  In 2008, only 15,395 were recorded during the peak count.  While some Red Knots winter in the southern United States, others migrate from as far away as the southern end of South America.  The two to three week stopover in Delaware Bay each spring is critical to the Red Knot’s ability to finish the migration north to its Canadian Arctic breeding grounds and to successfully reproduce.

Populations of horseshoe crabs in Delaware, New Jersey, Maryland and Virginia all influence the number of crabs spawning in Delaware Bay during the spring migration.  During the 1990s, the horseshoe crab became an increasingly popular as commercial fishing bait until the dramatic decline in population prompted the need for increased management efforts.  While harvests have been reduced in some states, the population count remains low.  Consequently, the availability of eggs during the Red Knot’s migration remains limited.

Additional Information

At least three petitions in the past have been submitted to the Fish and Wildlife Service (FWS) to list the rufa population under the Endangered Species Act. While acknowledging the declining population, FWS determined that listing was “warranted but precluded” by higher priorities.  In December of 2008, FWS elevated the status of the rufa on the Candidate Species List to a level three - the highest level possible for a subpopulation - with the recognition that the threat from low horseshoe crab populations is ongoing and therefore the danger of extinction is imminent.