Red Knots on Ocracoke in winter. Photo: P. Vankevich

By Peter Vankevich

The number of shorebirds that winter along the beach on Ocracoke varies from year to year.

Some years, Red Knots can be seen foraging alongside the usual Sanderlings and Willets. Red Knots with their legendary migration distances have drawn lots of attention due to their rapid decline over the past 20 years.

Worldwide there are six recognized subspecies of Red Knots that in breeding season, have a circumpolar distribution in the high Arctic and then migrate to coasts around the world. The Rufa Red Knot (Calidris canutus rufa) is the only subspecies that is on the Atlantic coast of the United States and the subject of this profile.

In winter, their appearance, called basic plumage, is that of a typical plain large gray sandpiper with a whitish belly and a faint supercilium (eye stripe).  The bill is black, and legs are dark. They can be confused with Short-billed Dowitchers which have a longer bill and a distinctive “V” pattern in the lower back. Another possible misidentification are Dunlins which can be present on the island, sometimes in great numbers in the fall and early winter. They are smaller and have a noticeable longer down-curved bill.

A Red Knot in breeding plumage. Photo: P. Vankevich

In breeding plumage (called alternate), there is no confusion.  The face, neck, breast and much of the belly are a brick-red color and the back and top of the head is mottled gray and black.

Egg laying begins around mid-June with clutches of three to four eggs. Their ground nests are lined with grasses and leaves of nearby plants, often willows in sparsely vegetated, dry, sunny, slightly elevated tundra locations that are not far from wetlands.

Both the male and female incubate the eggs over a period of about three weeks. The chicks are precocial at hatching, covered in down, and they and the parents move away from the nest within a day of hatching and begin foraging. The female departs before the young fledge while the males stay on to provide protection. After about three weeks when the young have fledged, the males begin their migration south, leaving the young to make their first migration on their own.

On their breeding grounds, they have a loud variable fluty song, especially in flight. In winter, they are mostly silent.

On Ocracoke, Red Knots can be identified from a distance by their behavior. They tend to move around in flocks that can number up to 100, though usually they number in the dozens or less. If you see a tight number of feeding shorebirds along the beach or a large number in a low flight pattern over the water, that’s a good sign they are knots.

Red Knots have been recorded on roughly half of the Ocracoke Christmas Bird Counts with a high number of 1,208 in 2015. 

On May 1, 2020 I did a survey of about four miles of Ocracoke beach and came across several flocks of Red Knots voraciously foraging. I estimated there were one thousand, in addition of lots of Sanderlings and  Willets.

Although some Red Knots winter in the United States with Florida having the highest numbers, most winter in Tierra del Fuego, the southernmost tip of South America. From there to their nesting area in the middle and high-Arctic areas of northern Canada, is one of the longest migration routes for a bird–9,000-plus miles.

In order to make this journey, they stop along the eastern seaboard, especially the Delaware Bay region, to rest and refuel. They arrive emaciated from their long journey from South America and need to stock up and gain weight immediately.

Red Knots. Photo: P. Vankevich

For much of the year Red Knots eat small clams, mussels, snails and other invertebrates, swallowing their prey whole – shell and all. But during  this long migration, they need easily digested foods –with thin or no shells – to gain enough weight to continue their migration. The best food source is horseshoe crab eggs, which are high in protein and fat allowing the birds quickly gain enough weight to survive the remaining flight to the Arctic.

Over the centuries, Atlantic horseshoe crabs (Limulus Polyphemus) have come into spawn at the same time the knots and other shorebird species arrive. This balance was upset by over-harvesting, which have diminished them in great numbers along with their eggs, causing catastrophic problems for the knots. Without this high-energy food, the knots are not able to make it to their nesting area, or if they do, they may be too exhausted to breed. 

Horseshoe crabs will not be found on the menu of a seafood restaurant as they are harvested by the commercial bait industry for catching whelks and eels. In the past, they were used for fertilizer. They are also harvested by the biomedical industry for their blood which contains an extract called L.A.L., used by the biomedical industry to detect certain bacteria.

Then they are released back into the water, but it is believed that up to 20% do not survive and the surviving females may not produce eggs after the extraction. According to reports, a synthetic substitute could eliminate medical harvesting, but it has not yet been approved.

Red Knot feeding on horseshoe crab eggs. Mispillion Harbor, Delaware. Photo by Gregory Breese/USFWS

Horseshoe crab harvests are now managed with explicit goals to stabilize and recover Red Knot populations, but the numbers have been slow to return to levels from just a few decades ago.

Red Knots have suffered a dramatic decline–as much as 75% or more in numbers since the early  2000s. In 2014, the U.S. Fish and Wildlife Service (FWS) listed them as threatened under the Endangered Species Act (ESA) and blame was placed on the excessive horseshoe crab harvests.

A discouraging news story by the N.J. Spotlight on May 20 reported there were only a few Red Knots on the New Jersey Delaware Bay shore where historically, they should have been in thousands. The reason is the horseshoe crabs had not yet arrived largely because unusually cool weather has kept the ocean temperature below what it needs to be for the crabs to spawn.

Another threat to Red Knots is climate change. These shorebirds and other species are facing a shrinking tundra, rising seas, ocean acidification and increasingly stormy weather. The warming, acidic sea inhibits the growth of the shellfish the birds need to fuel their impressive migration. Rising temperatures threaten to shrink their Arctic nesting grounds and expose them to more predators such as the Arctic fox.

Best time to see: Highest numbers are from May through early June, Variable numbers from late August through April.

Where: Along the beach

Listen: The Macaulay Library at the Cornell Lab of Ornithology has a variety of Red Knot recordings. Click here to listen.

Birds of the Outer Banks Checklist

Red Knot on Ocracoke. Photo: P. Vankevich
Red Knots in flight. Photo: P. Vankevich

 

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