Red Knots are plump, neatly proportioned sandpipers that in summer sport brilliant terracotta-orange underparts and intricate gold, buff, rufous, and black upperparts. This cosmopolitan species occurs on all continents except Antarctica and migrates exceptionally long distances, from High Arctic nesting areas to wintering spots in southern South America, Africa, and Australia. Red Knots from eastern North America have declined sharply in recent decades owing in part to unsustainable harvest of horseshoe crab eggs, and they have become a flagship species for shorebird conservation in the twenty-first century.
Look for Red Knots on sandy beaches and mudflats along the coasts during migration and winter (May and September are the best times in much of North America). Though their nonbreeding plumage is an indistinct gray and white, you can quickly learn to recognize the plump shape, medium-length bill, and relative size—larger than Sanderlings, smaller than Willets.
Red Knots often feed by sight but can also probe into sand or mud and use their sense of touch to find invertebrates below the surface. Their bill tips have specialized sensory organs, called Herbst corpuscles, which alert them to differences in pressure, a good clue that a clam or other meal is nearby.
Like most birds, knots have a preen gland at the base of the tail that secretes a waxy oil. When preening, they cover their feathers in these protective waxes by bringing the bill to the gland, then rubbing the bill across and under the feathers. As the breeding season approaches, the chemical composition of this wax changes to a form that mammalian predators can’t smell so easily. Both male and female Red Knots incubate their eggs, so both produce the less scented wax during the breeding season. In other shorebird species in which only the female incubates, males do not adjust the composition of the wax they produce.
When Red Knots eat mollusks, they swallow the shells whole and crush them up in the muscular part of their stomach, known as the gizzard. Recent studies indicate that knots have the largest gizzards, relatively to body mass, of any shorebird.
Red Knots concentrate in huge numbers at traditional stopover points during migration. Delaware Bay is one important area during spring migration, where the knots feed on the eggs of spawning horseshoe crabs. Nearly 90% of the entire population of the Red Knot subspecies rufa can be present on the bay in a single day. The reduction in food available to the knots because of the heavy harvesting of horseshoe crabs is in part responsible for a sharp decline in Red Knot populations.
The oldest recorded Red Knot was at least 18 years, 11 months old. It was banded in 1999 in Delaware and recaptured and re-released during banding operations there in 2016.
Sandpipers
