Red knot

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Calidris canutus

Type: bird

Status:

Species Guide

Red knot

Calidris canutus

Species Type: bird

Conservation Status:

Identification

During migration to and from its breeding and wintering grounds, the red knot rests and refuels here in New Jersey. It arrives here in May in its breeding plumage and again in September while molting into its non-breeding plumage. In its breeding plumage (May-August) the red knot has a distinctive breast feathers. They are distinctively colored a brilliant rusty red. This rusty red color extends up the neck and around the eyes. It bleeds somewhat into the patterned black, brown, gray and white colorations on the wings and back. The rump is whitish. The knot has a short, straight black bill. In its breeding plumage the legs are dark brown to black. Some adults arrive in the middle of their molt showing various amounts of the non-breeding plumage. Non-breeding plumage is typically seen between September and April, and is a washed-out gray look with scaly white feather edgings, whitish flanks with dark barring. The legs turn a greenish color. Juveniles are primarily gray, with a scaly pattern on the wings and dull yellow-olive legs.

Distribution & Habitat

Distribution and Habitat

Red knots begin arriving in New Jersey in early May. They continue to arrive in Delaware Bay where the population peaks to around 20,000 birds by mid-May. The average peak number of knots on Delaware Bay has dropped significantly since the late 1990s, generally attributed to a decline in their main food, horseshoe crab eggs. Red knots range from Fortescue south to Cape May in New Jersey and from Port Mahon south to Cape Henlopen in Delaware (Clark et. al. 1993). Major concentrations of knots may be found at Reed’s Beach, Cook’s Beach, Norbury’s Landing, and Fortescue.

Red knots on Delaware Bay depend primarily on horseshoe crab (Limulus polyphemus) eggs for food, and Delaware Bay hosts the largest spawning concentration of horseshoe crabs on the East Coast. Knots concentrate in high numbers in areas of dense horseshoe crab spawning, generally beaches that have gentle slopes with little wave action. When not actively feeding, knots may roost on the high portions of sandy beaches along Delaware Bay, but usually fly to roosts on the Atlantic side of the Cape May peninsula. Roost areas may be the long sandy spits at ocean inlets, as well as the numerous marsh islands scattered between North Wildwood and Sea Isle City. Birds also roost on sandy beaches and spits on Egg Island and Fortescue on Delaware Bay.

In the Arctic, nesting red knots use a distinctive habitat type. Vast areas of low tundra that are sparsely vegetated are preferred by knots to nest. These areas remain mostly covered in snow until mid-June. Birds must build nests in areas swept free of snow by prevailing northeasterly winds. Foraging habitat often consists of extensive isolated or wetlands that are dominated by sedges.

On southbound migrations, shorebirds, and their foods, are more dispersed across marsh flats and sandy washes. In New Jersey, many knots can be found along the Atlantic coastal beaches in August and September. They feed and roost there with several other species of shorebirds as they slowly make their way to wintering areas in southern South America. Occasionally large concentrations can be found anywhere from the Little Egg Harbor Inlet south to Wildwood Crest.

In their wintering areas, knots primarily occur on large tidal flats. Red knots roost in expansive sand flats that are only infrequently flooded by tides. Most of the wintering population occurs in Bahia Lomas, Tierra del Fuego, Chile. Birds there feed on a large sandy flat five miles wide and more than 40 miles long (Niles et al. 2001b). They roost along the water's edge.

Diet

When red knots arrive in New Jersey from their wintering areas they have little to no fat reserves remaining. Knots burn all of these fat reserves and sometimes even muscle to reach the Delaware Bay. Their migration is timed to take advantage of the concentration of spawning of horseshoe crabs, whose eggs provide a rich food source. Knots gorge themselves on the crab eggs to build up their fat reserves. These fat reserves will allow them to fly directly to their breeding grounds in the Arctic. Most double their weight in Delaware Bay, from only 110 grams to 185-220 grams before leaving and continuing their migration to breeding grounds in the high arctic. If some individuals do not gain enough weight or build up enough fat, then they may not reach their breeding grounds with enough reserves to survive and lay eggs.