Sand, Salt, Sun and Birds

Land Hermit Crab (Coenobita clypeatus).  This hermit crab lives in a variety of shells and may be seen walking beaches and climbing trees.  Florida Keys, Florida.  Jan, 2011.

Land Hermit Crab (Coenobita clypeatus) crawling under mangroves.

We should preserve every scrap of biodiversity as priceless while we learn to use it and come to understand what it means to humanity.
     –E. O. Wilson

It is January, but the hot sun bakes the coral beaches of the Florida Keys.  Humidity is constant except when a rare breeze sweeps by.  Clouds are an unfamiliar sight here, and when they arrive they drop rain and quickly move on.  My bare feet sit in the warm Atlantic water off of Lower Matecumbe Key as my eyes scan the sky for one of the island’s top predators, the osprey.

The Florida Keys are a chain of islands that curve from Miami south and west toward the Gulf of Mexico.  Ecologically, they are wonderfully diverse islands for their size, featuring a large variety of birds along with a handful of mammalian species, reptiles, amphibians, and a plethora of invertebrates.  The Atlantic Ocean and Gulf of Mexico provide a bounty of food which drifts in with the tides.  The osprey I frequently see and hear are accompanied by an occasional bald eagle, both species of bird feeding primarily on fish caught fresh from the ocean (though once while I was photographing some gulls, I witnessed a bald eagle snag one of them and rip the feathers out from atop a telephone pole).  American crocodiles also inhabit the mangrove swamps and artificial canals of the islands, remaining the top land predator, though hunting in the water.  Some of the mammals that are restricted to the land are smaller versions of their northern mainland counterparts, for instance, the key deer is a smaller version of the whitetail deer; and Vaca raccoons are paler and smaller than the typical Eastern raccoon.

Near where I work is a small, public beach that I enjoy walking in and exploring.  Unlike most beaches, the shore is made up of coral dust, which hardens like cement.  The islands were created by coral when sea levels were much higher.  During the most recent Ice Age, water froze at the poles and sea levels dropped–exposing the coral reefs.  The coral died but their skeletons remained and collected debris and floating seeds, thus forming the Florida Keys.

The water remains shallow for nearly a mile in some areas of the islands–one could walk out into the ocean a half mile before getting their bellybutton wet.  Out in these shallow waters is perfect hunting for wading birds.  Herons, egrets, ibis, terns, gulls, and spoonbills are among the birds that can be seen wading with tourists.  Cormorants and the anhinga typically swim in the water and dive for food in the deeper boating channels.  A flock of some of the wading birds nests on a nearby small island aptly named Bird Island–I visited once for only five minutes and found nothing but bird droppings and mangroves.

The tides bring in kelp and sea grass, which are fed on by tiny insects and other invertebrates.  In turn, these shoreline decomposers are food for a wide variety of shore birds including sandpipers.  The spotted sandpiper is a distinctly quirky bird–bobbing its tail up and down constantly as it scans debris for food.  Also hunting along shore are a variety of land crabs that dart into their holes upon sensing anything large.

An inland boardwalk is shaded by lignum vitae, gumbo limbo, and mangrove trees.  In the morning, the boardwalk bears footprints of raccoons and rats, and tree limbs are bridged with spider silk.  Mornings also reveal a wide array of birds flitting from shrubs and trees.  Warblers abound in the subtropics in the Spring, and they are not the only migrants here.  A yellow-bellied sapsucker scales a palm tree, licking at its row of taps much like it does in the northern forests of maple and oak, pine and spruce.  I have also found cardinals, blue jays, mockingbirds, catbirds, mourning doves, and ruby-throated hummingbirds, and–even though it contradicted every field guide I consulted–a small group of barn swallows.  The migrants mix with the year-round residents and wage war on every insect population on the islands, though it doesn’t seem to deter the mosquitoes much.

Any trip to this area of the country is not complete without a swim in the saltwater.  A weekend of snorkeling reveals just as much life under water as there is above.  Swarms of jellyfish float above coral landscapes tickled with fish.  Sharks and barracuda patrol the water and should be observed safely and not startled.  Overall, the experience is worth the risk.  The clear water teems with a variety of tropical fish, crabs, and crustaceans.  Seeing a manatee or a sea turtle is an unforgettable experience.  Manatees frequent boats and docks because of the freshwater that is dumped from them, which manatees need to drink to survive–the sea cows are often slashed by boat propellers because of this habit.

While many of the species seem to thrive, some are in great decline.  A large and growing population of Eurasian collared-doves threaten native ground doves and two endemic species– the Key West quail dove and the white-crowned pigeon.  Less obvious is a small-scale lizard war between the native green–or Carolina–anole and its invading cousin, the brown–or Bahama–anole.   The largest lizard in the Florida Keys is the beloved green iguana–many people even set out food for them.  However, the iguana is not native and is far more aggressive and opportunistic than some of the native animals in its niche.  Rats were among the first invasive species and are also among the most destructive both to man and native species.  Introduced mynas and starlings form aggressive flocks that steal tree cavity nest sites from native woodpeckers.  Deforestation and other introductions led to the extinction of Southeastern North America’s only native parrot species, the Carolina parakeet.  Many of the invasive species are family pets that were released or escaped, such as lion-fish, ball pythons, and an overwhelming number of feral cats.  Some exotic plants also thrive in the subtropical islands and threaten native species in the same niche.

The threats the islands face are many.  Hurricanes and seasonal storms topple trees and flood the land, chemical pollutants poison soil and sea, and invasive species crowd an area with limited space and food.  But the Florida Keys thrive still.  Fish from the sea feed birds that then fertilize the land with nutrients from the sea.  Tides bring food for invertebrates which feed the smaller birds, some of which are migrants from as far as Canada and South America.  Some plants drop seeds that wash away and can survive for years at sea until they land on shore somewhere and germinate.  A deprived and poisoned sea gives nothing to the land and the rich ecosystem on it.  The sea ultimately provides for the islands and the islands give in to the will of the sea.

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