Red Knot Races Tide and Time

Chris Haney, Ph.D., Defenders of Wildlife Chief Scientist 

For such a relatively small bird, the robin-sized red knot (Calidris canutus) has an extraordinary migration journey. Each year it travels more than 9,000 miles from breeding grounds high in the Canadian Arctic down to remote Tierra del Fuego in South America, where it spends the winter. To survive the trip, these shorebirds must be strong, healthy and resilient.

Horseshoe crab (©Spakattacks/Flickr)

But the red knot is struggling to overcome catastrophic population loss. Over the past ten years, the North American Atlantic population of the red knot (Calidris canutus rufa) has plummeted by 80 percent. Numbers of red knots have crashed by as much as 54 percent on their wintering grounds in two years alone. In New Jersey, where red knots stop to rest and eat before continuing their north-bound journey, they have been declining at a rate of 17.9 percent annually. So what is responsible for the species’ alarming decline?

Commercial over-harvesting of the prehistoric horseshoe crab is a key culprit. Red knots must concentrate in huge numbers at traditional stop-over sites to refuel during their migration, because a single non-stop flight can cover as much as 5,000 miles. Delaware Bay is a key staging area during spring migration, where knots come to feed on eggs of the once-numerous spawning crabs. Some estimates place nearly 90 percent of the entire North American Atlantic population of the red knot on the bay during a single day in May.

When red knots descend on Delaware Bay this spring, famished from their marathon flight from South America, they might find slim pickings instead of their expected feast of eggs from horseshoe crabs. Superstorm Sandy last fall scoured away much of the sand that crabs need for spawning. Restoring beaches is a top priority for wildlife groups who wish to repair massive damage to the dunes, beaches and salt marshes along the Eastern Seaboard.

(©Jan van de Kam)

Aided by grants from the National Fish and Wildlife Foundation and others, two feet of new sand covers stretches of beach along swaths as much as 5,000 feet long and 10-15 feet wide. Arriving in 20-cubic-yard dump trucks, one load at a time, enough sand has been dumped to cover about 1,000 cubic yards a day. Sand was targeted for spreading on the most well-known and crucial spots for both the horseshoe crabs and red knot.

This beach replenishment is hoped to provide just enough space for throngs of horseshoe crabs as they crawl out of the bay. Each spawning female will lay up to 100,000 eggs.

Despite the restored habitat, problems for the red knot are not over. Beach restoration will complement other measures, namely a continued closure of the commercial fishery for horseshoe crabs. But with its conservation plight now so well-known and supported, perhaps tide and time are turning for this remarkable shorebird.