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Shell Mound

October 4, 2010

In the middle of Estero Bay, half way between the Fort Myers mainland and Fort Myers Beach in Florida is Mound Key, a 140-acre island comprised primarily of the discarded remains of shellfish. Centuries ago, the Calusa lived along the gulf coast of Florida from Tampa south to the Everglades. Mound Key was thought to be the ceremonial center of their civilization and over the course of thousands of years, the fishery dependent culture developed several massive middens. At an elevation nearly 40 feet above sea level, Mound Key is the highest point in Lee County, Florida.

It’s hard to imagine the amount of shells necessary to create such a pile, and these days it’s not particularly easy to see either as Gumbo Limbos, Red, White and Black Mangroves and other subtropical trees now dominate the landscape. From a lookout at the apex of what is now a state park you can survey the gulf waters, the bay and the mainland. The height of this particular mound would have given the Calusas a visual advantage over invaders as well as protection from storm surges.

Snail Kites (Rostrhamus sociabilis) thrive in a similar fashion. I watched an endangered kite perched on a dead Sabal Palm (Sabal palmetto) trunk and upon approach I noticed the “boots” or dead fronds of the tree were decorated with empty Apple Snail (Pomacea sp.) shells. Snail Kites feed exclusively on the semi-aquatic gastropods, hovering over the shallow lakes and canals, swooping down and fishing an unsuspecting snail from the water. They usually find a perch to rest on and feed while they watch for winged pirates who might take their prize away. They use a deeply hooked beak to pluck their prey from the shell before discarding the now empty home. Many kites use a perch repeatedly and in a short time an amazing mound of shells begins to form.

After witnessing the debris that one escargot-eating bird can create in a few weeks, it becomes easier to imagine how thousands of Calusas, over several millennia can create the impressive mounds that they did.

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