Red knot

Red knots eat small clams, snails, worms and crabs.

In the Arctic they eat insects.

On the coast, red knots eat small animals that live in the mud and sand: mostly small clams, mussels and snails, plus worms and crustaceans (animals such as crabs and shrimp). They swallow the shells whole and crush them in the gizzard, a strong muscly part of the stomach.

On tidal flats a knot probes the mud with its beak and finds food by touch. In the Arctic it picks insects, especially flies, from the ground. When it first arrives there, before insects are about, it eats shoots, buds and seeds.

The USFWS calls red knots of all six subspecies specialized molluscivores: hard-shelled molluscs are swallowed whole and crushed in the gizzard, which is the largest relative to body size of any shorebird species measured. They prefer thin-shelled prey, rarely wade in water deeper than 2 to 3 centimeters, and can reach only prey buried in the top 2 to 3 centimeters of sediment. Audubon notes probing by touch on tidal flats and feeding by sight on dry sand and tundra.

On the breeding grounds the diet is mainly insects (especially flies, butterflies and moths, caddisflies, beetles and bees), with spiders, snails and worms; on arrival, before insects are active, knots depend on plant food such as sedge and horsetail seeds and grass shoots (IUCN). Outside the breeding season they take bivalve and gastropod molluscs, crustaceans, horseshoe crab eggs, worms and insects (IUCN).

Some red knots fly from the bottom of South America to the Arctic every spring.

They stop on beaches to rest and eat.

Some red knots of the rufa subspecies fly more than 9,300 miles (about 15,000 kilometers) north every spring, from the tip of South America to the Canadian Arctic, and fly back again in autumn. The US Fish and Wildlife Service calls them some of the longest-distance migrants in the animal kingdom.

On the way, knots stop at a few places where food is plentiful. In Delaware Bay, in the eastern United States, they feast on horseshoe crab eggs in spring and can nearly double their weight in about two weeks.

The IUCN describes a full long-distance migrant that uses few stopover sites. The USFWS says some rufa knots fly more than 9,300 miles (about 15,000 km) from south to north each spring and up to 19,000 miles (about 30,600 km) a year, among the longest migrations known; they travel in single-species flocks, departing flocks tend to be large (more than 50 birds), and they are thought to fly by both night and day.

Delaware Bay is rufa's main spring staging area: 50 to 80% of the population makes its final Atlantic stop there, and knots can nearly double their weight in two weeks on horseshoe crab eggs (USFWS). In Britain, the BTO says most wintering knots come from Iceland, Greenland and the Canadian Arctic, and mid-winter peak counts on The Wash have risen to about 200,000 birds. Where they are common, knots may roost shoulder to shoulder in packed flocks (Audubon).

There are fewer red knots than before.

They need muddy beaches where they can stop, rest and eat.

The red knot is listed as near threatened, and its numbers are going down. There are about 2 to 3 million adult red knots.

Knots need rich feeding places along their routes. Along the Yellow Sea, in East Asia, more of the coast has now been turned into dry land than is left as mudflat, and an invasive cordgrass appears to be spreading over the mud. In other places, collecting too much shellfish leaves less food, and tourists, people walking on beaches and aircraft flying over can disturb feeding birds.

BirdLife International assessed Calidris canutus as Near Threatened for the IUCN Red List (A2bcd+4bcd; assessed 10 July 2024, published 2024): global declines of 10 to 29% are suspected, largely from habitat loss and degradation, hunting and disturbance, and perhaps also as-yet-unidentified threats linked to climate change. The population is put at 2 to 3 million mature birds; generation length is 6.4 years.

On the Yellow Sea, reclaimed land now exceeds the remaining intertidal mudflat, and invasive Spartina alterniflora cordgrass is degrading what is left. Other named threats are over-harvesting of shellfish, disturbance from tourism, beach foot traffic, recreation and aircraft, and hunting, a probable threat in parts of the range. In the past, heavier harvesting of horseshoe crabs in Delaware Bay reduced the knots' food there (IUCN). China and South Korea have halted new projects that depend on land reclamation (IUCN 2023, via the assessment).