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Image: Florida Fish and Wildlife

Copperhead snakes are the most commonly encountered type of snake in the southern parts of the US state of Alabama ... but it wasn't always that way. The eastern indigo snake Drymarchon couperi, the longest native North American snake, once slithered along the forest floors there and helped control the rest of the snake community with its eating habits – dining not just on copperheads, but also on the venomous cottonmouths, rattlesnakes and others. The beautiful creatures, jet black with a hint of blue, are fairly docile and completely harmless to humans.

But the last time an indigo was seen in Alabama was in 1954. They've simply disappeared.

Though the indigo snake hangs on to existence in southern Georgia and some parts of Florida, it has vanished from southern Alabama and Mississippi. In 1978, the species was classified as threatened under the US Endangered Species Act. At first, conservationists thought they could re-establish the species in Alabama simply by rounding up some snakes from other places and releasing them into southern Alabama's Conecuh National Forest. But as is so often the case in wildlife conservation, things aren't quite that simple.

That's in part because the indigo snake is inextricably linked to the ecosystem in which it evolved. Longleaf pine forests once covered nearly 150 million acres and swept through nine US states, from eastern Texas to southern Virginia. This was at one time among the most biologically diverse terrestrial ecosystems outside of the tropics. "Longleaf pine ecosystems may be North America’s least appreciated repositories of biodiversity," wrote Bruce Means, an ecologist who has been working in the Florida panhandle for more than forty years.

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Without gopher tortoises to keep them warm in the winter, indigo snakes declined. Image: FWC Fish and Wildlife Research Institute

But the last century and a half of human development has seen the longleaf pine ecosystem become increasingly degraded and fragmented, with much of the forests' historic range converted for agriculture and urban development. As the forests disappeared, so did their inhabitants, including one cold-blooded reptile of great importance to the indigo snake. 

Gopher tortoises excavate deep burrows in the ground to avoid freezing during the cooler winter months, and indigo snakes evolved to take advantage of those burrows, cosying up to the tortoises as temporary roommates during the most frigid parts of the year. But as the forest was altered, gopher tortoises began to decline, which in turn led to a decline in indigo snakes.

Both gopher tortoises and indigo snakes were also collateral damage in the targeted killings of eastern diamondback rattlesnakes. The rattlers also rely on gopher tortoise burrows for shelter, which led people to gas the burrows in an effort to smoke them out. The rattlesnakes reliably flee the burrows upon gassing, but the indigo snakes and tortoises do not. They remain inside the burrow, where they suffocate.

Reintroducing the indigo snake into a severely degraded ecosystem is a fool's errand, but lots of work in recent years has gone into conserving parts of the longleaf forest that are still intact and to reclaiming areas that have become overrun with other tree species. In 2010, it became illegal to gas gopher tortoise burrows. In addition, gopher tortoises have recently become officially recognised as a high priority for conservation thanks to their role as a longleaf pine ecosystem keystone species.

But how do you go about saving a species anyway?

Gravid female indigo snakes (gravid, rather than pregnant, is the term used for animals that lay eggs) were first captured from wild populations in Georgia. Once they laid their eggs, they were returned to the spot from which they were removed. The eggs hatched under incubators at Auburn University, and the hatchlings were then raised for two years at Zoo Atlanta or at a non-profit facility devoted to reptile conservation in Florida called The Orianne Society.

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Image: Jason Goldman

Once they began to mature, rather than send the snakes directly into the wild from their captive origins, the snakes were first exposed to a natural environment – sun, wind, weather – in a protected concrete enclosure near Auburn University. As soon as they were put into the enclosures (lovingly referred to by herpetologist Jimmy Stiles as a snake 'halfway house') they began acting more like wild snakes. If a human caregiver approached too closely, for example, they would coil into a defensive posture.

After the orientation process, some of the snakes were implanted with small radio transmitters so that researchers could keep track of them. They were then brought to Alabama's Conecuh National Forest, where 80 were 'hard released', which means they were dropped into the forest to begin the rest of their lives. Eighteen others were 'soft released', a process pioneered with birds and mammals that affords the snakes some measure of protection while they adjust to the new environment. This was the first known attempt at soft-releasing a reptile species.

To soft-release the snakes, researchers constructed large pens within the forest, each containing at least one gopher tortoise burrow. All of the snakes eventually found their way out of the pens on their own, and observations have indicated that they're acting very much as wild snakes. They migrate during the breeding season, utilise similar habitats as their parents in Georgia and eat the animals they're supposed to eat.

"[They're] are not wolves," says Auburn University researcher Dave Steen, but as apex predators, their reintroduction might be comparable to the re-establishment of the wolves in Yellowstone National Park. Over the next few years, Steen and others will be monitoring the Conecuh ecosystem to see how it changes in response to the arrival of the indigos. With 98 released so far, there are plans to release around 200 more in the coming years.

Preliminary data suggest that they are doing their job as top predators, suppressing the populations of other snakes. Steen is hoping to determine how that might affect ground-nesting birds like quails and turkeys, which often lose eggs to rat snakes and corn snakes (which are also on the indigo snakes' menu), as well as how it might affect small mammals.

For Steen, what unfolds will be crucial for our understanding of predators, since most of what we currently know about predators comes from studying warm-blooded animals. Could the indigo snake be the next poster child for predator conservation?

Top header image: GTM NERR, Flickr