Recent conservation successes with Indigo Snakes - Drymarchon couperi - Reptilenesia

This article is part of a series highlighting new research in snake biology presented by herpetologists at the World Congress of Herpetology VII in Vancouver, British Columbia. If you want to learn more about the WCH, check out the June 2012 issue of Herpetological Review, or follow the Twitter hashtag #wch2012, with which I will tag all posts in this series.

An Eastern Indigo I was very fortunate to see in 2010.

Ask anyone: the Eastern Indigo Snake (Drymarchon couperi) is one of the most commanding and majestic snakes anywhere. Once found throughout Florida and in the coastal plain of southern Georgia, extreme south Alabama, and extreme southeast Mississippi, today the Eastern Indigo survives in numbers only in peninsular Florida and southeast Georgia. Although the species persists in low numbers in the Florida panhandle, it has been extirpated from the rest of its range as a result of declines in and alterations to the longleaf pine (Pinus palustris) ecosystem that it inhabits and on which it critically depends.

One of the largest snakes native to North America, D. couperi is one of five species belonging to a genus that ranges from Georgia to Argentina. Closely related to Racers (Coluber), Patch-nosed Snakes (Salvadora), and Whipsnakes (Masticophis), Indigo Snakes are charismatic and harmless. Carl Kauffeld called them "truly handsome and impressive" in his classic 1957 book Snakes and Snake Hunting. My herpetology professor, Whit Gibbons, told us a story of an exotic dancer who called his lab asking to borrow one to use in her show. This was during the early 1970s, when Eastern Indigos were common in the pet trade, before their federal listing under the Endangered Species Act (one of the first and still one of the only snakes ever listed).

A Gopher Tortoise basks at the entrance of its burrow. When fire suppression closes the canopy, their basking and egg-laying microhabitat is lost.

Unfortunately, Indigo Snakes are one of North America's most endangered snake species, primarily as a result of habitat destruction and fragmentation. Research by Natalie Hyslop showed that male Indigo Snakes in southeastern Georgia have home ranges as large as 3,000 acres (nearly five square miles), and one male Indigo Snake moved a distance of about 13 miles (22 km) over two years. As anyone familiar with the southeastern United States knows, it is almost impossible to find five square miles without a road interrupting it, and, as a result, many Indigo Snakes are run over and killed as they cross busy highways and interstates. Conservation of such a highly mobile species is extremely difficult, and by the early 2000s, population strongholds in Georgia were limited to two military bases, Fort Benning and Fort Stewart, where large tracts of uninterrupted sandhill habitat still remain. Furthermore, the degradation of longleaf pine sandhills via fire suppression encourages the growth of hardwood deciduous trees that close the canopy and push out Gopher Tortoises (Gopherus polyphemus), the burrows of which are critical Indigo Snake microhabitats during the winter breeding season. Although habitat degradation is the most insidious factor contributing to Indigo Snake declines, over-collection for the pet trade and malicious killing (both intentional and collateral, as when gasoline fumes are pumped down a tortoise burrow to kill rattlesnakes) are also considerable threats.

In 2008, a non-profit group called The Orianne Society was founded with the purpose of saving the Eastern Indigo Snake from extinction, which seemed inevitable given the rate of land development and habitat degradation in the southeast. TOS has advanced Indigo Snake conservation in a myriad of ways, from acquiring and restoring land to captive breeding. At the Mopani Indigo Snake Preserve in south-central Georgia, TOS biologists are tracking Indigo Snakes using wildlife detector dogs, also used to track other elusive wildlife, from whales to bats to salamanders. Last winter, I was generously invited to witness firsthand the effectiveness of CJ and his handler, biologist Kiley Briggs, at tracking Indigo Snakes at Mopani.

Indigo Snakes are known to feed primarily on other snakes, lizards, turtles, small mammals, frogs, and birds. Juveniles might feed on fish in the wild, because they spend the early part of their lives in mesic lowland areas and readily consume fishes in captivity. Unusual food items, in comparison to that of other snakes, include small Gopher Tortoises and all venomous snake species native to the Southeastern US (including Copperheads, Cottonmouths, Coral Snakes, and several rattlesnakes). For this last reason, Indigo Snakes generally have a more positive reputation than other snake species among rural residents of the southeast.

Sign alerting motorists to the presence of Indigo Snakes

At the WCH7, Jim Godwin, a zoologist with the Alabama Natural Heritage Program, and Jimmy Stiles, a student with  herpetologist Craig Guyer at Auburn University, brought us good news regarding the Eastern Indigo Snake in Alabama. Due to the collaborative efforts of over a dozen institutions and organizations, including the Alabama Department of Conservation and Natural Resources and TOS, captive-reared Eastern Indigo Snakes have recently been released into Covington County, Alabama's Conecuh National Forest. These snakes were born in captivity from wild females caught in Georgia and head-started at Zoo Atlanta. The plan was to test the effects of a hard (unpenned) or soft (penned) release on snake survival by following snakes with radio telemetry, but the 1-hectare pens built to contain the soft release animals "are just a suggestion to the snakes", according to Godwin. Instead of waiting the intended 90 days soft release period, many of the soft-release snakes released themselves 5-90 days after their initial release, by going under the fence. Because the snakes were implanted with radios, their progress could be followed. Fortunately, the team found that there were no significant differences in survival between snakes that had been hard and soft released, and that hard and soft release snakes had similar sized home ranges. Significantly, the percent overlap between male and female home ranges was higher for soft release snakes, and this effect increased with time spent in the enclosure. In terms of management implications, releasing snakes in pens does not seem to have a negative effect on snake survival and probably ultimately has beneficial effects on the structure of the established population. Earlier attempts to reestablish Eastern Indigo Snakes in Alabama were unsuccessful, possibly both as a result of the hard release techniques used and the release of too few snakes in too many locations. In the two years since the initial release in 2010, most of the Conecuh Indigos have survived, although several have been killed by predators and several more run over by cars. Improvements in the fire management regime in the Conecuh and continued research on the reintroduced snake population should mean a bright future for the Eastern Indigo Snake in Alabama.

Clearly I could write about Indigo Snakes all day, but if you want to learn more, check out The Orianne Society's website or read some of the papers linked in the References section below.

ACKNOWLEDGMENTS

Thanks to Mark Wallace for his photo of the happy volunteer.

REFERENCES