MERGING MIGRATIONS

     During a full moon, or new one, in May, when tides are highest in Delaware Bay, several hundreds of thousands of horseshoe crabs, which are really related to spiders and scorpions, migrate across the bottom of the bay and emerge on its gravelly/sandy shores to spawn.  For several days, lines and masses of "crabs", some rows up to a hundred yards long, cover many shorelines. 
     Many crabs are already paired when they crawl a few inches up Delaware Bay beaches, the males clinging on top of the larger females.  Each female lays thousands of tiny, dull-green eggs in the sand and gravel as she moves up the beach a little, dragging her mate with her, who fertilizes her eggs as he passes over them.  After spawning, each pair retreats again to the bottom of the estuary, leaving the eggs to their fate.
     Each adult horseshoe crab averages a foot and a half long, including the tail, and almost a foot wide.  Their dull-brown shell is the shape of a horse's hoof, and there are several legs under that protective covering.
     Horseshoe crabs, as a species, have remained virtually unchanged in coastal waters for over 500,000,000 years.  The American species lives along the coast, and estuaries, from Nova Scotia to Mexico, including, and especially, in Delaware Bay.  And there are a few other kinds along the west Pacific coast bordering east Asia.  
     Meanwhile, as the crabs spawn in masses, swarms of laughing gulls, semi-palmated sandpipers, sanderlings, ruddy turnstones, dunlin and red knots, the latter four kinds being shorebirds, too, land among the horseshoe crabs spawning on Delaware beaches to eat as many crab eggs as they can.  One can hear the loud, constant laughing of the summering gulls as they feed, while the migrant shorebirds gorge on those eggs to regain fuel before the next lap of their migrations north to raise young on the Arctic tundra.
     The merging migrations of hundreds of thousands of northbound shorebirds, along with the hundreds of gulls and hundreds of thousands of spawning crabs, create one of the grandest natural spectacles in North America.  Lucky are those people who witness this great orgy of spawning and ingesting, to the benefit of the birds.
     The knots have flown all the way from the southern tip of South America.  These chunky sandpipers with robin-red underparts, have flown the greatest distance of these shorebirds.
     Along many stretches of beach, hordes of shorebirds together clamber over and around the spawning crabs and feed on the crab eggs as fast as they can.  And, periodically, often with seemingly no provocation, the gulls and shorebirds suddenly dart up into the wind and away in the air.  Spectacular masses of airborne shorebirds swirl time and again over the bay and beaches, all twisting and turning together, all flashing brown, then white, in precision, without collision, then quickly settling on the area of crab eggs, like peanuts thrown across the beach, and immediately begin feeding again.  
     The tundra doesn't thaw until mid-May, or later.  The sandpipers' migrations are instinctively timed to get those birds on the tundra by the latter part of May, when they will lay four eggs per clutch and hatch fuzzy, precocious young that will soon be able to run and feed themselves. 
     The horseshoe crabs' spawning, therefore, is good fortune for the north-bound shorebirds.  That spawning coincides with the passage of those migrating shorebirds, giving them ample food for the next part of their journies.
     This great merging of migrations along the Delaware Bay, and elsewhere, is a wonderful, natural spectacle to experience.  It is one of the many exciting, inspiring happenings in nature that capture our imaginations and give us joy in God's works.