Red Knot’s future is not rosy.
The number of Red Knots visiting the Delaware Bay beaches during this spring’s northbound migration dropped to its lowest since tallies began almost 40 years ago. This is about a third of the number found in 2020, and the lowest since the early 1980s when the population was about 90,000.
The latest drop brings the small shore bird species—which has been federally listed as threatened since 2014—closer to extinction.
Every February, Calidris canutus rufa leave their winter home at the far tip of South America. They work their way north along the coast until they make it to Brazil when, flying in flocks of thousands, they travel across the Atlantic Ocean to their Arctic breeding grounds. The birds make a critical stopover at the Delaware Bay to refuel before continuing on. An estimated 90 percent of the entire species population can be found on the Bay—including at Raybin’s Beach in our Glades Wildlife Refuge—in a single day. They spend two weeks feeding before resuming their migration to the Arctic Circle.
Red Knots at Raybins Beach
Photo: Bill Moses
A key component of the Red Knot diet is the eggs of Atlantic horseshoe crabs (Limulus polyphemus). With timing that only nature could orchestrate, these prehistoric creatures leave the ocean depths to spawn on the moonlit beaches. The eggs, full of fat and protein, are the ideal fuel for hungry Red Knots, which have lost up to half their body weight by the time they arrive at Delaware Bay.
“It’s a remarkable sight when they arrive by the thousands,” said Brian Johnson, preserve manager at Glades Wildlife Refuge and avid birder. “Their migration route is one of the longest in the avian world. It’s a privilege to witness a part of it here at Glades.”
Unlike 2020, when unusually cool water temperatures for most of the month of May prevented many crabs from spawning at their usual time, there were plenty of crabs for the Red Knots to eat this year.
Dr. Larry Niles, an independent wildlife biologist who has monitored shore birds on the Bayshore for a quarter century, believes last year’s glitch in timing is likely responsible for the drastic decline this year. Dr. Niles estimates 40 percent of the Red Knots died in 2020 before they reached the Artic because they just ran out of energy for the journey.
Because of a clotting agent in their blood, horseshoe crabs have been used by the pharmaceutical industry for decades, despite the development of a synthetic, cost-competitive alternative. Although harvesting is now banned in New Jersey, it continues in Delaware, Maryland, and Virginia.
Many naturalists believe a complete ban on harvesting female horseshoe crabs is the best hope for the Red Knots, whose survival has come to represent the whole Delaware Bay ecosystem for Dr. Niles.
“We can’t stop bad winds or cold water, but we can expand the population of horseshoe crabs so birds arriving in most of these conditions find an abundance of eggs.”
“What we’re trying to do is not just bring back the bird,” he told reporters. “The bird represents the dysfunction in the system. This ecosystem is being robbed of its basic natural resource.”