Sand Ridge Ecosystem in Autumn

In the low country of south Georgia are ridges of sand populated by gopher tortoises and eastern indigo snakes, and this is where I spend much of my autumn–winter. Along the banks of many blackwater streams are deposits of fine coarse sand (carried and dumped by strong southwest winds that prevailed during the Pliocene–Pleistocene) up to 30 feet deep. These “eolian dunes,” veritable mountains in the otherwise flat and swampy Coastal Plain, provide excellent habitat for tortoises and indigos. The locals refer to the loose white to yellow-gray soil as “sugar sand.”

Sandridges are vegetated with a unique assemblage of drought-adapted plants—like saw palmetto, prickly pear cactus and sand spike-moss— that persevere in nutrient poor and xeric environments.  In this ecosystem, rainwater rapidly percolates through the sand before seeping into floodplain swamps downslope. A great thing about my profession (i.e., a surveyor of snakes of sandridge habitats) are my frequent peregrinations of these elegant, albeit austere, habitats. Stunted turkey and bluejack oaks, their limbs clothed with Spanish moss; patches of bare white sand freckled with lichens; the rich forest green leaves of the evergreen live oaks. It’s a landscape “easy on the eyes.”

This field season is our 2nd year monitoring the indigo snake in the Altamaha River Basin, a region that represents a population stronghold for the snake.  By annually surveying dozens of sandhills scattered throughout the drainage, we will be able to detect population trends over time. Indigo snakes we find on our surveys are weighed, sexed, measured, and marked (with a microchip [i.e., PIT tag] implanted just beneath the skin). We also measure the cloacal temperature of the snake—so that we may compare snake body temperature to that of the snakes’ environment (Let me say that inserting a small glass theremometer into the musk-drenched cloaca of a freshly-captured and wide awake seven foot indigo snake is, hmm, an interesting adventure).

This year, I have been privileged to visit some unique sandhills along the Ohoopee River, where rare plants more typical of central Florida scrubs, including rosemary, thrive. At these sites wonderful shrubby mints in the genus Clinopodium are the dominant ground cover. Walking from tortoise burrow to tortoise burrow finds me continuously brushing  against and breathing the pleasantly aromatic scarlet-flowered basil (Clinopodium coccinea). What a way to spend a day afield!

With scant surface water and limited cover, sandhills are rigorous habitats, especially during the infernal heat and humidity of a south Georgia summer. Many of the animals that live here are fossorial, clandestine, nocturnal, or only active seasonally. Eastern spadefoots, oldfield mice, pocket gophers, and two gorgeous sandhill snakes that resemble shiny candysticks (scarlet snake, coral snake) are all species that spend most of their lives underground. And, then there’s the venerable gopher tortoise, an excavator extraordinaire (tortoise burrows are often 8 feet deep and 25 or more feet long in the deep, sandy soils of south Georgia); and two giant, beautiful and iconic snakes that habitually use tortoise burrows: the eastern indigo snake and the eastern diamondback rattlesnake.

What makes tortoise burrows so attractive to indigo snakes, why do the snake use them? We know that in Georgia and north Florida indigos rely on the burrows for winter dens: during the coldest (and hottest) months, the bottoms of tortoise burrows—deep, dry but humid, cave-like and thermally stable—hover around 50-60 °F, a cozy temperature for a snake. Indigos like to shelter in them prior to shedding their skins, a period during which snakes are possibly more vulnerable to predators. Indigos also utilize tortoise burrows when seeking refuge from fires, during mating season, for foraging and for nesting. I have oft heard that on some of these remote sandridges where indigos are still common, there are fewer eastern diamondbacks—due to the indigos’ penchant for eating snakes, including venomous species. While there may be some truth to this, large expanses of quality habitat support resident populations of both (and those really large rattlesnakes are simply too big for indigos to ingest). I have enjoyed many snake surveys on mild winter days where we found a large adult indigo near one gopher burrow, only to walk 50 feet and find an enormous eastern diamondback lying close to another hole.

This autumn has been a rewarding time to be afield surveying for indigo snakes. Every day in the field is new. Discoveries await. To carry, as I do, the omnipresent anticipation: Will I stumble on some beautiful indigos today? Isl there a plump rattler coiled in the palmettos near that burrow? And I can tell you that our delicious autumn weather, and drawing in the wonderful smells of mints and goldenrod, has only added to my happiness.

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