Department of Fisheries and Wildlife
 

Factors limiting the migratory shorebird community in Delaware Bay and Coastal Virginia : Implications for the management of bird populations and the horseshoe crab fishery, 2004-present

Collaborators: Jim Fraser, Jonathan Cohen, Jim Berkson, Eric Hallerman, Dave Hata, Virginia Tech


 picture of shorebirds and horseshoe crabs

Left to right: A red knot with a newly attached radio-tag,
horseshoe crab eggs and the crabs themselves in Delaware Bay.


 Picture of redknot migration

Red knots (Calidris canutus rufa) migrate nearly 20,000 miles
roundtrip each year from their wintering grounds in Tierra del Fuego,
South America to the Arctic, stopping over only briefly in northern
Argentina, northern Brazil, and in Delaware Bay and coastal
Virginia to refuel.

 Picture of a redknot

Close-up of a red knot caught
during northward migration on the
eastern shore of Virginia B. Gerber

What is the problem that we are addressing? More than 50% of the U.S. population lives along the coast. Development of our coastline threatens diverse ecosystems upon which humans and wildlife depend for clean water, food, and protection from storms. Long distance migratory shorebirds that stop along the U.S. coast serve as sentinels to changes in the quality of coastal ecosystems. These shorebirds are highly sensitive to anthropogenic changes in their stopover habitat where they have limited time to replenish their fat reserves before continuing to Arctic breeding or South American wintering sites. Many migratory bird populations around the globe are experiencing rapid declines.

The red knot (Calidris canutus rufa), exemplifies the problem. This species winters in South America and migrates to the Artic to breed, stopping on the mid-Atlantic Coast to refuel. The red knot population is declining precipitously and could become extinct by 2010 if current trends continue. As such, it is a Candidate for listing under the Endangered Species Act. The ability to determine which factors are contributing to the red knot decline would increase our understanding of the global shorebird crisis.

 Picture of a redknot

A red knot in Virginia receiving an
experimental satellite transmitter
to remotely track it throughout
its annual migratory cycle. B. Gerber

The red knot (Calidris canutus rufa), exemplifies the problem. This species winters in South America and migrates to the Artic to breed, stopping on the mid-Atlantic Coast to refuel. The red knot population is declining precipitously and could become extinct by 2010 if current trends continue. As such, it is a Candidate for listing under the Endangered Species Act. The ability to determine which factors are contributing to the red knot decline would increase our understanding of the global shorebird crisis.

It is important that we reverse shorebird declines, including that of the red knot, for several reasons: 1) the birds, and their unique and awe-inspiring long distance migration, have immense aesthetic appeal that is in danger of being lost forever, 2) shorebirds are important to the economy of coastal communities, bringing in > $20 million in annual eco-tourism revenue in the Delaware Bay region alone, and 3) conservation of shorebirds promotes responsible coastal development that will benefit other economic and cultural resources upon which humans depend. Currently, many fisheries, recreational beaches, energy development, and other human activities on the coast are either restricted to protect imperiled shorebirds or are under intense interagency scrutiny. Shorebird population management must be a part of any integrated approach to coastal planning, but many aspects of shorebird biology are still poorly understood.

 Picture of a redknot

A VTech student
measuresa red knot's
beak and head length.
B. Gerber

What have we learned about red knot ecology to address these problems? Although a blue-ribbon panel organized by the U.S. Fish and Wildlife Service suggested that the red knot population decline is primarily linked to a decline in horseshoe crab egg availability at the knot's Delaware Bay migratory stopover site, our research shows that red knots are not currently limited by egg availability in Delaware Bay even though they continue to decline. Moreover, our recent work on the Eastern Shore of Virginia has shown that at least one-third of the population refuels in Virginia and, in 2006 and 2007, these birds did not feed on horseshoe crab eggs and rarely stopped in the Delaware Bay before continuing to the Arctic. Our work is the first systematic study of red knots in Virginia and has documented the importance of this stopover site as being second only to the Delaware Bay. Even less is known about the breeding ecology of red knots. Changes in tundra vegetation associated with climate change may reduce red knot reproductive success, and could negate the effects of managing horseshoe crab harvest or other U.S.-based coastal management efforts. Nevertheless, horseshoe crab harvest has been severely restricted or eliminated by various regulatory agencies to protect the red knot and other shorebirds. Horseshoe crab fishery regulations impact not only food availability for shorebirds, but also the sustainability of the horseshoe crab harvest by the bait and biomedical industries.

 Picture of a redknot

We use cannon-propelled nets to
catch red knots for radio- and
satellite-transmitter attachment.
B. Truitt, The Nature Conservancy

What more needs to be done? Alternative hypotheses for the red knot decline need to be explored while studies of the horseshoe crab link continue. Other causes of the decline may include a negative effect of climate change on Arctic breeding habitat and habitat degradation on the wintering grounds and other migration staging areas (such as coastal Virginia). Only a thorough understanding of the ecology of shorebirds throughout their annual cycle will permit management that conserves natural resources while balancing the diverse needs of coastal stakeholders.

 Picture of redknots in flight

Red knots in flight during their
migratory stop in Virginia.
B. Truitt, The Nature Conservancy

The future: With continued funds from the National Marine Fisheries Service, our team will explore the importance of the Eastern Shore of Virginia to red knots as well as continue our studies of the horseshoe crab resource coast-wide and its importance for the bait and biomedical industries and shorebirds. This project is also serving as a cornerstone for new studies that we are just beginning on the potential impacts of offshore wind development along the U.S. Atlantic coast on migratory birds. Our ultimate goal is to conduct science that will allow us to sustainably harvest our coastal energy and fishery resources while protecting our natural and cultural heritage.

 Picture of redknots in flight

Jessica Bercume, a research technician
on this project, observing foraging
red knots at sunrise in Delaware

For more information on the work of our partners and collaborators, please see the following links: