Birds
Red Knot
Calidris canutus rufa · also called red knots, rufa red knot
For a few precise weeks each spring, the beaches of Delaware Bay fill with both spawning horseshoe crabs and the red knots that time their entire migration around them, gorging on crab eggs to nearly double their body weight before continuing a journey that will carry them all the way to the Arctic.
Overview
The red knot, Calidris canutus rufa, is a long-distance migratory shorebird that breeds in the Canadian Arctic and winters as far south as Tierra del Fuego. Its extraordinarily long migration, precise dependence on a single seasonal food source, and population decline tied directly to horseshoe crab numbers make it one of the more ecologically fragile and closely studied shorebirds in the Americas.
A migration built around one narrow window
Few birds illustrate the risk of specialisation as clearly as the red knot, whose entire migratory strategy depends on arriving at exactly the right place during the exact few weeks horseshoe crabs come ashore to spawn.
Status
Near Threatened, with populations declining significantly due to historical horseshoe crab overharvest at Delaware Bay and habitat loss at other key stopover and wintering sites.
Red Knot: common questions
Why does the red knot depend so heavily on horseshoe crab eggs?
This species times its arrival at Delaware Bay to coincide almost exactly with the brief spring spawning period of horseshoe crabs, gorging on their eggs to nearly double its body weight in a matter of days, fat reserves that are essential fuel for completing the final, demanding leg of its migration to Arctic breeding grounds where food is not yet abundant on arrival.
Why did the red knot population decline?
Historical overharvest of horseshoe crabs at Delaware Bay for use as bait and in biomedical testing sharply reduced the number of eggs available during the red knot's critical migration stopover, leaving many birds unable to gain enough weight to complete their journey successfully, a decline compounded by habitat loss at other important stopover and wintering sites.
How far does the red knot migrate?
This species undertakes one of the longest migrations of any North American shorebird, travelling from wintering grounds as far south as Tierra del Fuego at the tip of South America to breeding grounds in the Canadian Arctic, a round trip covering many thousands of kilometres each year.
How can you identify a red knot?
Look for a rich chestnut-red face, throat, and underparts during the breeding season, a striking contrast to the duller grey non-breeding plumage the species wears for the rest of the year, combined with a stocky build and relatively short bill compared with many other similarly sized shorebirds.