Clams for Dinner

Currently, the beaches of Seabrook Island host a large flock of Red Knot, a species of bird severely threatened. Some Red Knots make an epic journey all the way from Tierra del Fuego at the southern-most tip of South America all the way to the scattered islands north and west of Greenland, approximately 9,000 miles. To date not enough information about Red Knots exists to say for certain what is happening with the Seabrook Island birds. One tiny tidbit of information came from a Red Knot with a geolocator, a device once placed on a bird records for up to two years the bird’s location. Only after a scientist recaptures a bird can they read the information. One Red Knot with a geolocator made a non-stop flight from Seabrook Island to James Bay in northern Canada.

To make these marvelously long flights, birds need to pack on weight! They need a good food source. The birds on Seabrook Island find that in the form of a little clam. Scientist call this clam Donax variabilis. We call it coquina, wedge clams, or bean clams. Every time one walks on the beach, those small white shells that crunch underfoot indicate the presence of Donax Clams. Look carefully at these shells and you will see that those on the beach have small holes near the umbo or beak of the clam. This indicates that clam fed a snail, probably an Atlantic Oyster Drill, Urosalpinx cinerea. The clams eaten by the Red Knots go into the bird’s gullet where it is ground to a pulp so the bird’s stomach can extract the nutrients.

Donax Clams never grow very large, a huge one measures just ¾ inch. The Red Knots prefer the smaller ones and their small size makes them easy for the Red Knots to capture and swallow whole.

The presence of filter feeding Donax Clams provide an excellent indicator of clean water and clean sandy beaches. We can feel certain that the clean beaches with fresh sand and lots of clams on Seabrook Island provide the major attraction to the Red Knots. The sheer number of Red Knots seen on Seabrook Island far exceeds any other reported locations along the Gulf of Mexico and the Atlantic Ocean coast during the months of March and April. That changes in May when the population shifts to the Delaware Bay shores of New Jersey and Delaware where the bird’s change from feeding on clams to feeding on Horseshoe Crab eggs, a tiny packet of pure fat and protein. This tiny preferred feeding area extending essentially from Deveaux Bank through Folly Beach is a critical staging area for these birds, with Seabrook and Kiawah Islands hosting the largest concentrations.

Beach users can help these birds prepare for their journey by walking around the feeding flocks.

Article and Photos by: Bob Mercer