Each year, horseshoe-crab eggs provide migratory birds with a critical food source.
In late May and early June, two great migrations converge simultaneously on the beaches of the Harbor Bight region. The first is the creeping progress of horseshoe crabs from the ocean floor toward the beaches, where they eventually spawn; the other is a northbound wave of shorebirds winging from wintering grounds in Central and South America toward nesting sites in the Arctic. At its peak, this annual gathering of millions of these ancient "living fossils" of the sea and huge numbers of long-distance fliers can still make for a powerful demonstration of the connections that often tie together far-flung and very different forms of life.
Horseshoe crabs have been around for some 250 million years. Dark, rust-colored hulks with long spikelike "telsons," or tails, they are indeed strangely prehistoric in appearance and are more closely related to spiders than to true crabs. For most of the year, horseshoe crabs crawl along the bottom of bays and along the continental shelf, feeding on marine worms and shellfish. But as the days lengthen in springtime, they begin to move toward the calm, bayside beaches of the mid-Atlantic to spawn. The males arrive first, massing in the shallows. Once the much larger females arrive, the full and new moons during May and June trigger an amphibious assault on the beaches. Droves of females haul out onto the sand, often with two or three males clinging onto their shells. Somewhere between the low and high-tide lines on the beach, females burrow six to eight inches into the sand and lay their eggs in this nest. Several nests may be laid during a beach trip, and females make additional trips on subsequent tides -- a single female may lay as many as 88,000 eggs per season!
These eggs provide critical nourishment to shorebirds journeying north from their winter homes to their Arctic breeding grounds. Some birds, such as red knots and tiny sanderlings, may have traveled several thousand miles nonstop over open ocean before dropping exhausted on the shores of estuaries of New York and New Jersey. Without the renewed energy this immense and ready food source provides to these birds, they could never complete the final leg of their migration.
Sadly, this annual feeding and breeding frenzy is in deep decline. Overharvesting of the crabs (used to bait eel pots, among other things) has reduced their numbers to a fraction of their former abundance. And as the dense hordes of egg-laying crabs have thinned out, the refueling stop the birds have relied on for eons has become less reliable. In this way, a web of life that extends nearly from pole to pole and has evolved over millennia is unraveling. For example, about 80 percent of the western hemisphere's red knots stop in the Delaware Bay; counts of red knots wintering in South America show a decline of more than 50 percent since 1986.
Where to See Them: Although Delaware Bay is the best known area to witness this migration spectacle, many areas in the Harbor Bight region -- including Jamaica Bay Wildlife Refuge, Fire Island National Seashore and Horseshoe Crab Cove in Sandy Hook, New Jersey -- offer important habitats for spawning horseshoe crabs' and shorebirds' migratory stopovers.
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Heron Rookeries: Large, long-legged "waders," herons and egrets are a graceful presence at water's edge throughout the Harbor Bight region. They are communal nesters, and colonies often contain a mix of species.
One such colony is the Harbor Herons Wildlife Refuge, three small islands situated in the Arthur Kill, an ocean waterway separating Staten Island from New Jersey. Once a highly polluted area, this is now the largest colony of herons in New York State; summers bring about 1,200 nesting pairs of nine heron species, including great egrets, snowy egrets, black-crowned night herons, glossy ibis, yellow-crowned night herons and little blue herons.