Horseshoe crab and shorebird bonanza!

2013-04-29 horeshoe

Horseshoe crabs gather in large groups at nesting beaches in the days surrounding full and new moons.

Having inhabited the oceans for over 350 million years, horseshoe crabs (Limulus polyphemus) are a glimpse into prehistory. We spot them most often as dead carcasses or molts along the shoreline. However, right now we are seeing hundreds of live, healthy, active crabs at the waterline.

Birders at Sancho Panza marvel at the horseshoe crab "arribada."

Birders at Sancho Panza marvel at the horseshoe crab “arribada.”

Horseshoe crabs spend most of the year in deeper waters, but in the late Spring they begin to move inshore to mate in large aggregations. Hundreds are gathering at Sancho Panza Beach here on Little St. Simons Island. Mating activity peaks around the full moon and new moon cycles, and with the full moon last week, we found big groups of males fighting for the chance to fertilize some eggs, and several indentations in the soft, wet sand where undoubtedly nests had been left behind.

A female will push several clumps of eggs down into the sand with specially adapted appendages. Each clump can contain two to four thousand eggs, and over the course of her spawning season, a female will deposit around 90,000 miniature eggs! Of those 90,000 eggs, only about 10 are expected to mature into adult horseshoe crabs.

If you are familiar with our island, you know that Sancho Panza is an excellent shorebirding spot, and right now we are in the peak of Spring migration. It is quite the spectacle to see a variety of shorebirds eating to their little hearts’ content at the buffet of horseshoe crab eggs! In fact, horseshoe crabs are instrumental in the journeys of at least 20 species of migratory shorebirds along the Eastern Seaboard.

Ruddy Turnstone feeding at a horseshoe crab nest. (Photo: Pete Oxford)

Ruddy Turnstone feeding at a horseshoe crab nest. (Photo: Pete Oxford)

Sanderling feeding on horseshoe crab eggs. (Photo: Pete Oxford)

Sanderling feeding on horseshoe crab eggs. (Photo: Pete Oxford)

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