The meeting of tens of thousands of Atlantic horseshoe crabs and multitudes of several kinds of north-bound, migrant shore birds on sandy and gravelly beaches in May each year is one of the greatest natural spectacles along the shores of Delaware Bay. The "crabs" are there to spawn, while the bird gatherings are there to eat crab eggs. And I have seen the great numbers of crabs and birds converge several times over the years.
The "crabs", which are not crabs, but members of the arachnid (spiders and scorpions) family of invertebrates, live along the coasts of the Atlantic Ocean and the Gulf of Mexico. There they walk along the bottom and consume worms, small mollusks and crustaceans, and other little critters.
There are four species of horseshoe crabs in the world, three kinds along the shores of eastern Asia, and the Atlantic species. They are living fossils, having relatives back 450,000,000 years ago. Each animal has an exoskeleton shell, five pairs of legs, a long "tail" it uses to right itself if flipped over by wavelets. And it swims up-side-down, using its legs as paddles.
At high tides, during the day or night, when the moon is new or full, these crabs silently swarm onto many beaches to the high tide level from New England to Mexico. And each female of the many thousands spawns thousands of small, dull-green eggs in the wet sand. Each female is attended by one or a few males who fertilize their eggs in the sand, as wavelets wash over them. Many shore birds walk over the spawning crabs as they ingest those invertebrates' eggs. Then surviving parent crabs retreat to the water, leaving their offspring to their fate.
But the large swarms of noisy birds that gorge on horseshoe crab eggs in the sand are the most exciting part of this natural show. The most common of those birds include laughing gulls, sandpipers including dunlin, knots, turnstones, sanderlings, short-billed dowitchers and semi-palmated sandpipers, red-winged blackbirds and boat-tailed grackles. All these birds are packed together on the sandy/gravelly shoes of Delaware Bay, and elsewhere, where the crabs spawned or are spawning. These birds cause feeding frenzies, which are exciting for us to experience. They are "fueling" up on crab eggs to have the fat and energy to make the final part or their trip north to the tundra to nest. And while some shore birds are feeding frantically on the eggs, other flocks of birds are either coming to or leaving those sandy dining halls along the bay, adding to the excitement of the feeding birds. Each bird of a flock might gorge on crab eggs for a few days, then go north. But other birds coming from farther south take its place at the chow line. The comings and goings and feeding birds are too much to keep track of: It is just one big, overwhelming natural spectacle that one won't forget. It is a spectacular that gives one faith that at least some aspects of nature are still healthy and in charge of themselves; not depleted or extinct Although, over-harvesting of horseshoe crabs, if allowed to continue for fish bait and fertilizer, might negatively impact horseshoe crab populations and the numbers of the birds that depend on crab eggs to fuel up on to continue migrating north to the tundra. We need to continue to enforce laws that control horseshoe crab harvesting for any purpose, at least for awhile.
The striking gulls are the loudest and most incessant of boisterous birds of these great, shoreline gatherings. One can hear their loud, "laughing" calls, in chorus, almost anytime of day along the Atlantic coast and along back waters in from the ocean, including Delaware Bay beaches.
Over thousands of years, the sandpipers have timed their north-bound travels to arriving on the Delaware bay, and other backwaters along the northern Atlantic shore, when horseshoe crabs spawn. That way those birds get a few days of easy meals to put on fat before continuing their migrations north to raise young on the tundra of Alaska, Canada and Greenland.
These sandpipers have come far to nest on the tundra. Knots, for example, come from Tierra del Fuego of southern South America, while the semi-palms came from the coasts of Caribbean Islands and both shores of South America.
Horseshoe crabs and a variety of shoreline birds converge at high tides in May each year, the crabs to spawn and the birds to eat many crab eggs, creating an overwhelming show. Watch for when new or full moons occur in May to be able to experience the peak of horseshoe crab spawning and a variety of shoreline birds frantically feeding on many of those eggs before continuing their migrations to the Arctic tundra to nest.
No comments:
Post a Comment