Citizen Science Supports Shorebird Recovery at Delaware Bay
By Gregory Breese
Delaware Bay is home to the largest spawning population of horseshoe crabs in the world. It also hosts the second largest population of migrating shorebirds in North America. This is no coincidence—each spring, thousands of shorebirds flock to these shores to refuel on protein-packed horseshoe crab eggs before continuing their northbound migration.
Delaware Bay is an especially important stopover site for the federally threatened red knot (Calidris canutus rufa). Traveling from as far away as the tip of South America, these marathon migrants arrive at roughly a fat free weight and must eat enough to double their weight in just two weeks before resuming their journey to the Arctic to nest. Since the 1980s, the red knot population has fallen by about 75 percent in some key areas, largely due to declines in horseshoe crab eggs in Delaware Bay. A team of dedicated citizen scientists have joined federal and state biologists in the effort to study the health of the red knot population and ensure an adequate supply of crab eggs remain available for the rare shorebird.
Horseshoe crabs have been exploited for decades. They were used for fertilizer by early farmers, and where then later caught in large numbers and dried and chopped up for the commercial fertilizer. More than 4 million crabs were harvested for this reason each year through the late 1800s. More recently, the animals have been used as bait to catch conch (whelk), a recent fishery that expanded along East Coast in the 1990s. It is believed that this bait harvest caused their population to decline and jeopardized the ability of the red knot and other shorebirds to find adequate food.
To help ensure a successful migration, the U.S. Fish and Wildlife Service, in partnership with the Atlantic States Marine Fisheries Commission and U.S. Geological Survey, developed an adaptive management framework for setting harvest levels for horseshoe crabs by taking the needs of shorebirds into account through model, which recommend appropriate harvest amounts based on estimates of horseshoe crab and red knot populations.
To determine the number of red knots visiting the bay each season, teams comprising federal and state biologists and citizen scientists canvas the beaches lining both sides of the bay and record birds that are individually marked with coded leg bands. In addition, they sample the flocks and record the ratio of marked and unmarked birds. This information is not only used to estimate the size of the red knot population at Delaware Bay, but to determine arrival and departure dates of individuals, calculate stopover duration, assess patterns of site use by individuals, assess survival, and provide lifespan estimates as well.
Citizen scientists are a critical part of this effort. A team of 10 to 30 members are needed to help conduct daily surveys on each beach throughout the migration season. In addition to recording population data, citizen scientists also participate in catching and processing red knots to monitor weight gain and individually mark additional birds for this population analysis. The contribution of these volunteers will continue to support important management decision making in Delaware Bay.
Editor's note: Those interested in supporting red knot recovery are encouraged to volunteer as citizen scientists with the Delaware Shorebird Project.
Gregory Breese, a fish and wildlife biologist in the Service's Delware Bay Estuary Project office, can be reached at email@example.com or 302-653-9152.
Wildlife and Habitat Conservation
- Conservation Planning