Migration Numbers Plummet for Imperiled Shorebird on NJ’s Delaware Bayshore

Jon Hurdle | May 19, 2020 | Energy & Environment
Veteran biologist sees unprecedented declines in red knots — and in horseshoe crabs
Credit: Jon Hurdle
A pair of red knots in the foreground and two horseshoe crabs at Cooks Beach, Cape May County on Monday, May 18, 2020

At the mouth of a creek near Pierces Point, an isolated beach community on the New Jersey side of the Delaware Bay, Larry Niles spotted only two red knots on Monday morning, in the same place that he saw some 17,000 of the shorebirds during their spring migration a year ago.

It was a snapshot of a dramatic decline in the number of knots that have stopped off on the bay beaches so far during this year’s migration, a change that has no precedent in the 24 years that Niles, a wildlife biologist, has been monitoring the annual visits of thousands of knots and other shorebirds.

Nearly all the birds have stayed away from the bay this year because of a shortage of horseshoe crab eggs that fuel them for the completion of their long-distance migration from South America to breeding grounds in Arctic Canada. And the crabs are largely absent because unusually cool weather has kept the ocean temperature below what it needs to be for the crabs to spawn.

The lack of food on the Delaware Bay side of New Jersey has so far driven about 7,000 migrating knots to sites on the state’s Atlantic coast where they are feeding on “mussel spat,” a food source that isn’t as energy-rich as crab eggs, and so won’t do as good a job of fueling the birds for the rest of their grueling migration, Niles said.

In ‘ecological lockdown’

“Now, after a week of very few spawning crabs and virtually no red knots, we must see this year as truly different than all the others,” Niles wrote in an email to supporters on Monday. “And not because of the deadly COVID-19 virus. Cool weather, tropical storms and God knows what else seems to put the entire stopover in a sort of ecological lockdown. We don’t know what is next for birds and crabs.”

Credit: USFWS
Horseshoes crabs, Delaware Bay, 2019

By Monday, only about 150 red knots had been spotted on a section of the Bayshore between Reeds Beach and Pierces Point that usually hosts thousands of the birds and other species in May.

Niles blamed low air temperatures keeping the water at or below 59 degrees, the threshold for spawning. In most years, the water temperature rises to that level by early May, but this year that didn’t happen, and the weather forecast for the rest of May, with high air temperatures remaining in the 50s and 60s, suggests that’s not going to change.

In 2017, cool weather in mid-May shut down the crab spawn, making it hard for the birds to put on weight, but a late warming produced a surge in eggs, improving prospects for the rest of the migration.

But it’s hard to be optimistic about this year because of the weather forecast and Tropical Storm Arthur — the first named storm of the Atlantic hurricane season, whose easterly winds are pushing cold Atlantic waters toward the shore, lowering the air temperature, and hindering the departure of the few migrants that are ready to resume their northward journeys, Niles said.

Shorebird count much different from other years

His efforts have been further hampered by the need to follow social-distancing requirements in the COVID-19 pandemic for his seven assistants. That has meant cancelling the participation in this year’s shorebird count of dozens of volunteers who are normally drawn from all over the world to witness a great natural spectacle, and contribute to the survival of the red knot and other shorebird species, including ruddy turnstones and semipalmated sandpipers. And it means that the few remaining members of the team wear masks and strictly observe distancing measures to stop the spread of the disease.

Credit: USFWS
Horseshoe crab eggs

Because of the pandemic, Niles nearly cancelled the event for the first time in almost a quarter century but decided to hold it with the appropriate health precautions because he didn’t want to interrupt 23 years of data from one of the world’s most important shorebird migration sites.

“Information from the Delaware Bay is absolutely essential because it’s the one place where you have so many species and so many individuals coming through,” said Eric Stiles, president of New Jersey Audubon. “If you miss the field season, you could miss a huge uptick or a huge downturn.”

The cool weather wouldn’t be so much of a problem if it hadn’t been for the “senseless slaughter” of horseshoe crabs during the 1990s and early 2000s for commercial fishery bait and for bleeding by the biomedical industry, Stiles said. Although New Jersey has now banned the crab harvest, helping the bird population, it’s still allowed by other Mid-Atlantic states, and unknown numbers are taken for bleeding, preventing a recovery in the crab population.

Efforts to stop the biomedical industry from taking crabs recently suffered a setback when the United States Pharmacopeia (USP), a body that sets professional health-based standards for the pharmaceutical industry, unexpectedly delayed action on a proposal to endorse the use of a synthetic alternative to the crab blood, which it uses in a test for bacterial contamination in pharmaceuticals.

Synthetic alternative to crab blood for COVID-19 vaccine

Advocates for a switch to the synthetic substance say it could be used to test any vaccine that is discovered for COVID-19 in much greater quantities than the material that uses crab blood, while cutting the demand for crabs.

Credit: Jon Hurdle
Shorebirds massed last May at Reeds Beach, Cape May County to gorge on horseshoe crab eggs before resuming their migration to breeding grounds in Arctic Canada.

The effective absence of the red knot from the bay beaches so far this year renews concern about the survival of a species that the federal government listed as threatened in 2014. Since hitting a low of around 17,000 in the early 2000s, its numbers have stabilized at about 45,000, but they are still below the level that would allow the species to survive shocks like extreme weather or the new development of wintering or migration sites.

Some red knots, which weigh less than 5 ounces, migrate about 10,000 miles from southern Argentina to Canada — one of the longest migrations in the avian world — losing a significant amount of their body weight by the time they reach the Delaware Bay.

Without the crab eggs that allow depleted birds to regain weight during their brief stopover, they may be unable to complete their migration, may head north from the bay but die en route, or may fail to breed successfully, naturalists say.

“This week will be decisive,” Niles said. “If it (the weather) doesn’t turn around by the end of the week, then it will be difficult for the birds to make the weight needed for migration.”