Rufa Red Knot (Calidris canutus rufa)
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A robin-sized shorebird, the rufa red knot is truly a master of long-distance aviation. On wingspans of 20 inches, some knots fly more than 9,300 miles from south to north every spring and repeat the trip in reverse every autumn, making this bird one of the longest-distance migrants in the animal kingdom. The knot's unique and impressive life history depends on suitable habitat, food and weather conditions throughout a network of far-flung sites across the Western Hemisphere, from the extreme south of Tierra del Fuego to the far north of the central Canadian Arctic.
The rufa red knot spends most of the year in flocks, sometimes with other species. As the knot heads north to breed in the tundra of the central Canadian Arctic, its plumage becomes rusty red. The birds return to gray as they head south to wintering grounds at the southern tip of South America (Tierra del Fuego), in northern Brazil, throughout the Caribbean, and along the southeastern and Gulf coasts of the U.S. into Mexico. Rufa red knots feed on invertebrates, especially small clams, mussels, and snails, but also crustaceans, marine worms, and horseshoe crab (Limulus polyphemus) eggs. On the breeding grounds knots mainly eat insects. Migrating knots can complete non-stop flights of 1,500 miles or more, converging on vital stopover areas to rest and refuel. Birds arrive at stopover areas with depleted energy reserves and must quickly rebuild their body fat to complete their annual migrations. For example, during their brief 10 to 14-day spring stay in the mid-Atlantic, rufa red knots can nearly double their body weight.
Large flocks of rufa red knots arrive at stopover areas along the Delaware Bay and the U.S. Atlantic coast each spring, with many of the birds flying directly from northern Brazil. Spring migration is timed to coincide with the spawning season for the horseshoe crab, whose eggs provide a rich, easily digestible food source. Because it provides abundant horseshoe crab eggs, Delaware Bay is the single most important spring stopover habitat, supporting an estimated 50 to 80 percent of all migrating rufa red knots each year. Mussel beds and small clams on the Atlantic coast are also important food sources for migrating knots, in both spring and fall. Besides Delaware Bay, some key U.S. stopover habitats include the coastal islands of Massachusetts, Virginia, South Carolina, and Georgia. Some rufa red knots that winter on the Gulf coast take an overland migration route, stopping along the rivers of the Mississippi drainage and at saline lakes in the northern U.S. and southern Canadian plains.
Red knots in trouble
Rufa red knot populations in the U.S. were decimated in the 1800s by commercial hunting for sport and food. Knot hunting in the U.S. ended with passage of the Migratory Bird Treaty Act in 1918, and historical writings show the birds largely recovered. But in the 20th century, coastal development and overharvest of the horseshoe crab took a toll. Rufa red knot numbers in Tierra del Fuego (winter) and Delaware Bay (spring) declined about 75 percent from the 1980s to the 2000s. The smaller populations that remain now face many hurdles to recovery, including sea level rise; coastal development; shoreline stabilization; dredging; reduced food availability at stopover areas; disturbance by vehicles, people, dogs, aircraft, and boats; and climate change.
Road to recovery
The horseshoe crab harvest is now managed specifically for the protection of the rufa red knot. Knot populations appear to have stabilized in recent years, though at low levels. Listing of the rufa red knot in 2015 brought new protections. Some threats, like climate change, cannot be directly addressed under the ESA. But by limiting other threats – like horseshoe crab overharvest and human disturbance – the Service and our partners are giving the rufa red knot its best shot to adapt and cope with a changing world.
Learn more about our approach to recovery:
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