CONVERGING HORSESHOE CRABS AND SHOREBIRDS

     During May of 2021, I watched huge gatherings of horseshoe crabs and shorebirds on the mud flats and gravelly shores of Mispillion Harbor in the middle of the western shoreline of Delaware Bay in Delaware.  I watched those great congregations of creatures through a live camera mounted near the Dupont Nature Center, and our home computer in Lancaster County, Pennsylvania.  

     Horseshoe crabs are not crabs, but related to spiders and scorpions.  They are "primitive" relics from the long ago past and mostly unchanged since those ancient times.  

     Many hundreds of thousands of horseshoe crabs push up the sandy or gravelly beaches from Delaware Bay to spawn, day and night, during the full moon or new moon in May.  Each female "crab", and one or a few males attached to her, creep up the beaches like tanks.  And each female can spawn as many as 100,000 tiny, dull-green eggs in the sand or gravel of Delaware Bay beaches, including those in Delaware and New Jersey.

     Meanwhile, thousands of graceful, black-headed laughing gulls summering on the salt marshes and beaches of lower Delaware Bay and hundreds of thousands, up to a half or a whole million, of migrant shorebirds of several kinds create intriguing and inspiring spectacles when they converge to eat as many of those "crab" eggs as they can.  The shorebirds eat those fatty eggs to put on layers of fat for the next part of their migration north to the Arctic tundra to nest.  

     And one can hear the constant "laughing" cries of the laughing gulls as they forage for those eggs.  Many of those icons of the American seacoasts in summer were paired and courting in preparation for raising three chicks in ground nests in nearby salt marshes.

     As the horseshoe crabs spawned and laughing gulls laughed, shorebirds, including red knots, dunlin, ruddy turnstones, sanderlings and semi-palmated sandpipers, gathered by the swarms among the horseshoe crabs to eat their share of the crabs' eggs in the sand and gravel.  More of those attractive shorebirds arrived every day for a few days, reaching a peak in numbers around the middle of May.  Knots have robin-red underparts and dunlin are chestnut on top and have black bellies.  Turnstones are mottled chestnut, black and white. 

     Those great masses of shorebirds often take wing at once in a tremendous flock that speeds low over land and water, twisting this way and that at once.  But soon those birds, together, swoop down for a landing on the beaches, looking like someone tossed peanuts across the beach.  And those shorebirds immediately began ingesting horseshoe crab eggs as fast as they could.    

     And there was something humorous about those horseshoe crabs coming to shore to spawn.  Scores of diamond-backed terrapins climbed up on some of the crabs to bask in the warming sunlight while the crabs continued to spawn and birds ate crab eggs.  I never saw that part of the horseshoe crab spawning before.   

     The great horseshoe crab/shorebird convergence along Delaware Bay is one of a few incredible natural spectacles in the United States.  That inspiring happening, the sandhill crane gathering on the Platte River in Nebraska in April and the congregations of snow geese in early spring are unbelievable mass gatherings of wildlife that make a naturalist's heart sing.    

       

                   

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