Kicking Off Indigo Snake Survey Season



Indigo Surveys

Authored by Houston Chandler

November marks the beginning of our annual surveys for Eastern Indigo Snakes (Drymarchon couperi) and Eastern Diamondback Rattlesnakes (Crotalus adamanteus). Over the next five months (November to March), we will be searching for snakes on sandhills across South Georgia. This season’s surveys will take place at sites in three major river drainages: the Altamaha, Alapaha and Satilla. This will be our first season formally sampling sites in the Alapaha and Satilla drainages, and we are excited to see how many Indigos and Diamondbacks we find at these new sites. Expanding our surveys to include more sites will allow us to gain a better understanding of how Eastern Indigo Snakes and Eastern Diamondbacks are faring in Georgia.

Indigo Snake surveys target sandhills in South Georgia that still have large numbers of Gopher Tortoises (Gopherus polyphemus). Both Eastern Indigo Snakes and Eastern Diamondbacks use tortoise burrows as retreats during the autumn and winter months. Indigos frequently bask near burrow entrances on mild autumn and winter days and can be active at temperatures (circa 50° F) when most other snakes would be dormant. The cooler months are the best time of year to survey for Indigo Snakes because the adult population migrates from surrounding habitats (as far as three-plus miles away!) back to xeric sandhills where they are, with considerable effort, possible to locate. Indigo Snakes are unusual among Georgia snakes in that their mating activity occurs primarily during this time of year. Male snakes will participate in male-to-male combat, where competing males try to pin each other to the ground to assert their dominance and win the right to mate with a nearby female. Eastern Diamondbacks are less active during the winter than Indigo Snakes but can still be found basking near tortoise burrows on warm winter days.

Indigo Surveys

The main goal of our winter snake surveys is to identify whether or not each survey site is occupied by Eastern Indigo Snakes and/or Eastern Diamondback Rattlesnakes while accounting for the difficulty in locating these species even when they are present at a site. To accomplish this, we survey each site three times during the survey season. Each survey consists of walking sandhills and checking Gopher Tortoise burrows for basking snakes when weather conditions are suitable. If there is a shed skin or snake track near a burrow, we use a burrow camera (essentially a camera attached to the end of a 25-foot tube that can be fed down a Gopher Tortoise burrow) to look for snakes that are using the burrow as a retreat. All captured Indigo Snakes and some captured Eastern Diamondbacks are given a unique identification number using PIT tags, allowing us to identify individual snakes when they are recaptured in subsequent years. This season we will also be sampling snakes for Snake Fungal Disease (caused by the fungus Ophidiomyces ophiodiicola) by taking swabs from all captured snakes.

Some of the snakes that we have marked in past years will undoubtedly show up again this year, and by the end of March, we hope to have documented Eastern Indigo Snakes and Eastern Diamondback Rattlesnakes on many sites in Georgia, including some sites that were not occupied in previous seasons.