Dirk Stevenson (Altamaha Environmental Consulting)

Learn more about the movements of radio-tracked eastern indigo snakes and journey west as Dirk Stevenson draws comparisons between this charismatic gopher tortoise commensal and another pair of iconic species - and the burrows they share - in the Great Plains region of North America.

April. 

The massive eastern indigo snake awakens and crawls up the incline of the gopher tortoise burrow shaft, passing a sleeping tortoise along the way. His muscular form leaves a series of distinct sine-wave prints in the sand where his belly digs in, looking for purchase. A regal head, held high, watching, emerges from the burrow. He pauses, tongue-flicks, then slowly slithers from the tunnel into the daylight. Where the sun strikes his large dimpled and diamond-shaped scales, his color shines and reflects a purplish iridescence. If you were watching, you would be watching for some time and you would think, man, when will the end of the snake get here?!? Ten years old, the resident commander of the sandhill is well over seven feet long.

Moving on, he snakes past the fallen turkey oak limb where he shed his skin a few days ago, slides down the slope of the sand ridge toward a bay swamp where, resting on a thick carpet of sphagnum, he slurps from a perennial seepage. And now he really moves—coursing over a wet pine flat, across three primitive sand roads, through an oak grove, all the while on a southerly bearing. Slinking into a blackwater drain fringed with flowering titis, he finds a drying pool alive with bouncing leopard frogs. He suppers on these; for dessert, a small cottonmouth. By the end of the day, he has moved well over a half mile, dodging an overambitious red-tailed hawk in the process. An old rodent hole dug in the mound created by a large windfall serves as lodging.

The big indigo continues south, and by the end of the month, he has moved close to four miles from the sand ridge tortoise colony where he overwintered. Feeling exposed when swimming a moderate-sized blackwater river, he moves rapidly. Hunting is good in an extensive bottomland and adjacent hammock, where his summertime foraging sallies produce two adult woodrats and a three-foot timber rattler. Plus, it’s a wet year, and a wet year means lots of ranid frogs. When laying low, he noses into a cavity beneath the buttressed trunk of a giant tulip poplar. The earth is soon worn smooth at the entrance to this hole from his frequent use. 

Mid-October.

The male indigo, now stout-heavy with muscle and body fat, is restless. Two chilly nights are the trigger that send him northward, again crossing the river, again negotiating swamps, pinewoods and sand roads on his way back to the tortoise colony on the sand ridge. The very same sand ridge, where in November–December, after morning basking events to recharge his batteries, between intense fighting bouts with an upstart rival male (only 6 feet 9 inches), he will mate with two females, one of which he has previously sired young’uns with. 

Full disclosure: The above narrative is imagined but based closely on the experiences of my colleague and friend, herpetologist Natalie Hyslop of the University of North Georgia, who radio-tracked indigo snakes in Southeast Georgia for her PhD. Natalie’s exciting results documented long-distance dispersal and what are the largest home ranges known for any snake species native to the United States—3,500-plus acres for some of the large males she monitored.

There isn’t much an indigo won’t do in a tortoise burrow. Natalie was fascinated by the intimate association between the tortoise and the snake, a relationship especially pronounced in southern Georgia. She documented indigos using gopher tortoise burrows as refuges not just in winter but year-round, as shelters during ecdysis (skin shedding), for egg laying, and to escape temperature extremes and fire. Foraging snakes may search for prey in the burrows, and in an ironic twist, indigos commonly eat tortoise hatchlings.

The eastern indigo-gopher tortoise association is mirrored by that of the prairie rattlesnake-prairie dog. The prairie rattler, Crotalus viridis, is a grassland species and an iconic denizen of the Great Plains region of western North America. The species dens communally, sometimes on south-facing slopes associated with rugged bluffs, buttes, and other rocky landscapes, but it also has an inordinate fondness for prairie dog towns. 

Prairie dogs (there are five species), like gopher tortoises, are notable keystone species. Badgers, raptors, bullsnakes, and burrowing owls thrive in dog towns. The dogs maintain prairie conditions favored by the rare mountain plover. Like tortoise burrows, dog holes are deep (3–6 feet) and long enough (15-plus feet) to offer dry and thermally mild refuges for rattlers. In the 1930s–1940s, communal rattlesnake dens in the dog towns were targeted by professional snake control agents. Rattler dens in South Dakota averaged 250 snakes and some contained over 500 individuals. Good numbers of bullsnakes and racers shared the dens. During peak ingress/egress, the snake hunters killed rattlers by the hundreds, sometimes firing their rifles until their hands, and ammunition, were exhausted.

Our magnificent western grasslands, like our singular Coastal Plain longleaf pine-wiregrass savannas, have seen better days. Much of our native prairie, short grass and long, has been plowed, taken when the sod was broken. When we still had buffalo aplenty, the great dog towns went on for miles and miles. Today, some still exceed several hundred acres. Denning prairie rattlesnakes are known to take over a section of a dog town; the presence of large numbers of rattlers serves to evict the rodents from their burrows. Then over time, as the holes fill with earth, the snakes relocate to another section of the town. 

Like indigos, prairie rattlesnakes seasonally migrate significant distances (up to 11 km in Saskatchewan) from their dens before returning to them with the onset of cold weather in October. These movements often take them to optimal foraging grounds—namely, ground squirrel colonies. 

In late September, my wife Beth and I travel to South-Central Montana in search of adventure and prairie rattlesnakes. En route, we visit Yellowstone National Park, overnighting in a rustic cabin just outside the eastern edge of the park. The young woman who checks us in wears a ballcap with a moose on it, her ponytail sticking out of the rear of the cap. From our conversation with her: 

Cabin Employee: “You will want to carry bear spray at all times when on property. We are currently having some bear issues.” Spoken in the firm, authoritative tone one associates with law enforcement. 

Wife: “Oh, dear. A black bear?”

Employee: “Nope, grizzlies.” 

Wife: “Oh, wow! Do they come around during the day or night?”

Employee: “Both.”

The grizzlies were two-year-old males who had been evicted from the park proper by their mother or a large male, I can’t remember. They were said to hang out near the stream down the hill. 

Employee: “There is a bear trap baited with part of a dead elk just downslope from your cabin. You may see it. Be sure to carry bear spray.”

After supper, we stroll downhill (bear spray at hand) to the gorgeous Rocky Mountain stream. Yellow and orange leaves of aspens and cottonwoods catch the fading light. The temperature is plummeting. On a gravel bar along the stream, we nearly step on the fresh tracks of a grizzly bear.

Grizzlies become ravenous in late summer, prepping their bodies for hibernation. Makes me think of male indigo snakes, how they arrive at their sandhill mating grounds with solid bodies ready for battle and mate-searching. Soon after we leave the park, there’s a horrible tragedy: Grizzly Female 399, 28 years old and the mother of about that many offspring, is struck and killed by a vehicle in the park. Again, I think of indigos; crossing roads is dangerous. Natalie once tracked one of her favorite charges, a large male indigo named “Red”, to find him fresh-dead on a sand road, the victim of a vehicle strike. 

Beth and I find prairie dogs in semi-desert habitat west of Montana’s Pryor Mountains. An endless valley at the base of the mountains is populated with hundreds of giant wind turbines. It feels like a Hitchcockian tableau, the vast plain below the turbines, giant blades forever spinning, asynchronously. Flushed meadowlarks sail far in the wind. The dogs check us out, then dive into holes or resume nibbling. We fondle a hissing bullsnake, photograph a Badlands tiger beetle the color of an emerald, look for horned lizards, then get, and fix, a flat tire. No rattlers.

Our last day in Montana: glorious vistas, great weather. Soon there will be snow here. We hike a ridge and valley complex south of Billings that is peppered with sandstone outcrops,  always the pleasant aroma of a mint-green sagebrush species. We crest a hill to spook a mule deer buck who bounds off pogo stick-like, landing with his heels together. A pair of ravens fly sky loops together. The birds issue throaty gurgles, happiness in raven-speak, when they dive in tandem. Then, one takes off like a bat out of hell and starts bashing a soaring bald eagle.

At 10:45 we encounter our quarry. Moving toward us, up the hill above a small primitive cemetery, is a fine three-foot male viridis, his scales the washed-out greenish color that gives the species its scientific name. From the looks of his plump physique, he’s made a good living this year. Meaning he should survive another harsh Montana winter and then emerge next May to do it all again: migrate, shed, coil, hunt ground squirrels, mate—in short, be a prairie rattlesnake.