Red Knot Life History

Habitat

Habitat Shorelines

Red Knots nest in High Arctic habitats visited by very few people. In North America, they use dry tundra slopes with sparse stunted willow or mountain avens, often far from the coast but usually on warm, sunny slopes facing south or southwest. While incubating, knots forage in wetter habitats, usually not far from the nest. Once young are able to fly, they move toward sedge meadows and lakeshores, feeding heavily in preparation for their long migration. Migrating and wintering knots use marine habitats—sandy beaches, saltmarshes, lagoons, mudflats of estuaries and bays, and mangrove swamps that contain an abundance of invertebrate prey. Other habitats that might harbor knots include peat banks (remnants of ancient forest on the seashore, exposed by erosion), salt ponds, eelgrass beds, and Brazilian restinga (coastal spits). Red Knots occasionally appear at interior locations in eastern North America, where they frequent shorelines of large lakes or even freshwater marshes.

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Food

Food Aquatic invertebrates

Small bivalves, especially mussels and their larvae, clams, and cockles, form the largest part of knots’ diet for much of the year. They also consume amphipods, gastropods, marine worms, chitons, shrimp, and tiny crabs. In spring, eggs of horseshoe crabs in the Delaware Bay are important food for migrating Red Knots (subspecies rufa), whereas in western North America subspecies roselaari Red Knots consume eggs of grunion (a small fish) before moving northward from Mexico. Early in the nesting season in the Arctic, knots frequently feed on seeds and shoots of grasses but quickly switch to invertebrates as they become available. Small chicks consume insects, especially midges. Through most of the year, Red Knots pick or probe in sandy, muddy areas, often during falling tides, for marine invertebrates of many kinds. When feeding on small mussels, knots usually forage more slowly than smaller sandpipers, but they take eggs and larval mussels with rapid picking motions similar to other species.

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Nesting

Nest Placement

Nest Ground

Males select and prepare 3–5 sites for nest scrapes, normally dry, stony areas of tundra in upland areas, often near ridges and not far from wetlands. Vegetation is normally very sparse near the nest, typically willows and mountain avens.

Nest Description

The nest scrape, once selected by the female, is lined with grasses and leaves of nearby plants, often willows and avens, and finished with tubular lichens or bits of mountain-heather (Cassiope). Nest size averages about 4.7 inches across and 1.7 inches deep.

Nesting Facts
Clutch Size:3-4 eggs
Number of Broods:1 brood
Egg Length:1.5-1.8 in (3.8-4.5 cm)
Egg Width:1.0-1.2 in (2.6-3.1 cm)
Incubation Period:21-23 days
Egg Description:

Faint olive to deep olive-buff with dark markings, denser at large end.

Condition at Hatching:

Downy young leave nest almost immediately.

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Behavior

Behavior Ground Forager

Male Red Knots arrive before females on the nesting grounds and establish territories, which they mark with song flights and defend vigorously when other males intrude, sometimes in dramatic aerial chases. The song flight display, as with many Arctic-nesting shorebirds, is a joy to witness: male knots fly upward with trembling, rapid wingbeats, sometimes over 900 feet in the air, then glide earthward slowly, giving a lovely whip-ooo-mee vocalization. Males prepare up to five nest scrapes before females arrive, and they show each site to the female using a specialized call and display, in which males sit in the nest scrape, elevate the wingtips, and kick backward with the feet. In another less well-known courtship display, the male raises or lowers the tail, calling to the female with his hindneck distended. Knots are believed to be completely monogamous, at least seasonally. Both sexes participate in incubation. During migration and in winter, knots gather into flocks, forming tight roosts when at rest, as do many shorebirds. They often rest on their bellies on dry ground such as sand.

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Conservation

Conservation Declining

All three subspecies of Red Knot found in North America are in decline. The populations wintering in South America dropped by more than 50% from the mid-1980s to 2003 and the rufa subspecies is listed as federally Threatened in the United States. A 2012 study estimated the total number of all three North American subspecies at about 139,000 breeding birds. Partners in Flight estimates the global breeding population (all subspecies) at about 1 million individuals, rates the species a 13 out of 20 for its Continental Concern Score, and includes it on their Yellow Watch List for declining species. The IUCN Red List lists Red Knot as a Near Threatened species. The occurrence of large concentrations of knots at traditional staging areas during migration makes them vulnerable to pollution and loss of key resources, such as horseshoe crab eggs at Delaware Bay. Beginning in the late 2000s, changes to Maryland, Delaware, New Jersey, and New York fishing regulations helped alleviate some of the pressure on horseshoe crabs, and the rufa subspecies may be benefiting from this. The impacts of climate change and sea-level rise are expected to be most severe in migratory stopover locations. In parts of eastern South America and the Caribbean, the species is shot in large numbers for both food and sport, as formerly occurred in North America as well.

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Credits

Andres, B. A., P. A. Smith, R. I. G. Morrison, C. L. Gratto-Trevor, S. C. Brown and C. A. Friis. (2012a). Population estimates of North American shorebirds, 2012. Wader Study Group Bulletin 119 (3):178-194.

Baker, Allan, Patricia Gonzalez, R. I. G. Morrison and Brian A. Harrington. (2013). Red Knot (Calidris canutus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, USA.

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