Wednesday, October 21, 2009

The Amazing Journey of Red Knots to New Jersey

Red knots and Ruddy Turnstones at NJ's
Edwin Forsythe National Wildlife Refuge (USFWS photo)

Back in the early 1800s, the naturalist Alexander Wilson visited Cape May, N.J. There, he saw a bird he called the red-breasted sandpiper. He also saw horseshoe crabs. (He called them "king crabs.")

It took until the 1980s for scientists to really understand the global significance of the Delaware Bay as the springtime staging area for those birds, who we now call red knots. Those birds, and other migratory shorebirds, rely on being able to feed on horseshoe crab eggs.

Pete Dunne and others from the New Jersey Audubon's Cape May Bird Observatory, flew over the shores of Delaware Bay in May and early June and saw this staging area in action. They recorded red knots, sanderlings, semi-palmated sandpipers and ruddy turnstones.

Some of those red knots headed for the Arctic started their journey of migration 5,000 miles away in South America. Their journey is of international concerns. Computer models show that the Delaware Bay subspecies of red knots (Calidris canutus rufa) could within a year or two because the population is so depleted.

Amazingly, scientists are able to distinguish three populations of red knots that migrate through the Delaware Bay region. One group spends the winter on Georgia's Altamaha Delta and Florida's Gulf Coast. A second group spends the winter in Maranhao in northern Brazil, and the third, and largest group of about 18,000 red knots, spends the winter in Tierra del Fuego at the southern tip of South America.

Crowded areas include a large horseshoe crab eggs area at Mispillion Harbor on the Delaware side of the bay and a nighttime resting area in Stone Harbor, N.J. Red knots had rested on the marshes west of Cedar Creek, but in 2004 and 2005, those marshes flooded and the birds could not roost there.

Most scientists believe that overharvesting of the crabs in the 1990s has led to the severe drop in eggs and therefore the decline in red knot populations.

How large is the decline? Those 1981-82 flyover estimates were at 150,000 red knots. Recent counts totaled about 15,000.

In their time on the Delaware bay, the birds have about two to three weeks to put on enough weight to complete their journey. The numbers are staggering. Scientists estimate that each red knot needs 13,000 horseshoe crab eggs a day to maintain their weight and 24,000 eggs to fatten to the optimum.

In 1999, the red knot was listed as a threatened species in New Jersey under the "New Jersey Endangered Species Conservation Act." As a result of the Red Knot Status Assessment in Fall 2006, the U.S. Fish and Wildlife Service announced the red knot as a candidate for federal listing. In April 2007, the Committee on the Status of Endangered Wildlife in Canada recommended listing the red knot as endangered.

While the red knot is most imperiled and most studied shorebird on the Delaware Bay, there are five other species that rely on crab eggs and whose populations have declined on Delaware Bay by about 65 percent: Ruddy turnstone (Arenaria interpres), sanderling (Calidris alba), semipalmated sandpiper (Calidris pusilla), dunlin (Calidris alpina) and the short-billed dowitcher (Limnodromus griseus).

Tagging red knots - via fw.delaware.gov

2 comments:

  1. Nearly all the redknot data has been based on falsification. By way of manipulation of research data. USF&W service May 2003 Peer-revied that data and found NJ population data NOT usefull. Why do you still use it.

    ReplyDelete
  2. Anonymous,

    Where is your evidence of "peer reviews" and contradictory evidence?

    ReplyDelete