The mass migration of birds every spring and fall ranks among the greatest of natural wonders on our planet. Of the many avian species that migrate, a few make spectacular journeys that set them apart from their globetrotting counterparts. These marathon migrants cover many thousands of miles, sometimes non stop, over open oceans, deserts, mountain peaks and inhospitable terrain. Bar-tailed Godwits fly non stop across the Pacific Ocean from their breeding grounds in Siberia to their winter homes in New Zealand – a trip spanning 7,000+ miles. Bar-headed Geese fly at nearly 30,000 feet in altitude as they cross the Himalayas from their central Asian nesting areas to reach their winter homes in India. Several Old World warbler species, like the Blackcap, weighing a scant ½ ounce (~14 grams) cross the Sahara Desert every spring to reach their European breeding grounds.
Among the elite corps is the Red Knot, a medium-sized sandpiper that travels 20,000 miles round trip annually from Tierra del Fuego and Patagonia, at the southernmost tip of South America, to breeding grounds in the Canadian Arctic. They accomplish this primarily by flying 3-4 non stop long distance segments each way, with prolonged stopovers en route to rest and refuel. Those of us who are students of avian migration know the Red Knot well. On its way north, this shorebird lays over in Delaware Bay for 2-3 weeks, after a 3500-mile nonstop flight from coastal Brazil. They come to the Bay to fatten up before undertaking the last leg of their monumental trek across two hemispheres.
Delaware Bay is the last refueling stop for shorebirds on their way to the Arctic. The ability of Red Knots and other shorebird species to accumulate sizable energy reserves is critical to the successful completion of their journey and survival once they arrive in the Arctic. Food is scarce and the weather is unpredictable in early June when shorebirds arrive in the Arctic, making energy reserves brought from Delaware Bay the key to survival in most years.
Horseshoe crab eggs are the food of choice for Red Knots and several others in the sandpiper clan that stage in Delaware en route to the northern breeding grounds. The largest aggregation of horseshoe crabs in the world spawn on the beaches of Delaware Bay just as migrating shorebirds arrive to rest and refuel. However, over the past decade, horseshoe crab egg availability has declined dramatically as a result of over harvesting during the mid-late 1990s.
Studies conducted over the last 12 years by NJ Division of Fish and Wildlife (NJDFW), Delaware Department of Natural Resources and Environmental Conservation (DNREC), New Jersey Audubon Society (NJAS) and a team of international biologists have documented dramatic declines in the ability of shorebirds to gain weight during the Delaware Bay stopover period. Importantly, they have documented significant declines in shorebirds using Delaware Bay during spring migration that are concomitant with declines in horseshoe crab egg availability.
During annual expeditions to Tierra del Fuego (TDF) and Patagonia since 2000, NJDFW, Canadian Wildlife Service and South America biologists have documented similar declines of Red Knots on their wintering grounds. The focus of the work in TDF is to monitor changes in the wintering population of Red Knot and to capture and individually mark birds. The second element provides a way to track individuals along migration routes and to generate annual survival estimates for the population. This work suggests that overall survival rate has also declined from about 80% in the mid-late 1990s to 50% from 1999-mid 2000s. To see blogs posted by Larry during earlier TDF expeditions, and his unique perspective from this year's effort, click the following link (www.shorebirdproject.blogspot.com).
This year I have the great fortune of accompanying Drs. Larry Niles (Conserve Wildlife Foundation-NJ), Amanda Dey (NJDFW), Humphrey Sitters (British Trust for Ornithology) and Steve Gates (dedicated volunteer) on the 2007 TDF expedition. Although the work of NJAS's Research Department work in Delaware Bay focuses primarily on Semipalmated and Least Sandpipers, we have been collaborating with Larry et al. on shorebird conservation in Delaware Bay for over a decade. NJAS's Conservation Department has been at the forefront of political action to halt the harvest of horseshoe crabs and restore viable populations that can provide sufficient food for migrating sandpipers.
I write this first blog entry with great anticipation. It's my first trip to South America and I'm sure it won't be my last.
