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We recently wrapped up the 2021–2022 indigo snake survey season. This marked the 12th consecutive year that The Orianne Society has conducted visual encounter surveys for Eastern Indigo Snakes and Eastern Diamond-backed Rattlesnakes at sandhill sites across southern Georgia in coordination with partners at the Georgia Department of Natural Resources. On these surveys, we visually search for snakes with a small group of observers on a variety of public and private properties. Snakes spend the winter on sandhills because the presence of Gopher Tortoise burrows offer refuge from potentially lethal winter temperatures. Indigo snakes also use this time to reproduce, and it is not uncommon to encounter gravid females by the end of the survey season. These surveys are designed to monitor the number of potential overwintering sites that are currently occupied by these iconic snake species in southern Georgia. Surveys also build off of a long history of marking captured indigo snakes with subcutaneous tags, and these data will ultimately give us more information about both individuals and populations. This type of project is important when trying to make informed conservation and management decisions for rare species.
During each survey season, we visit 20 potential overwintering sites, and sites are on a 3-year rotation such that we survey a total of 60 sites over three years. Each site is visited three times during a survey season to account for the difficulty in actually locating snakes even if they are present. Over the course of 60 surveys conducted from November 2021–March 2022, we observed 44 Eastern Indigo Snakes and 26 indigo snake shed skins, which are easily identifiable based on their size and coloration. The largest of these snakes measured just under seven feet in total length. We also encountered 12 Eastern Diamond-backed Rattlesnakes, including eight individuals on the Orianne Indigo Snake Preserve. These observations are fairly similar to the last time that this subset of sites were surveyed. However, there were some notable observations. For example, we documented and marked indigo snakes on one property that had not had any confirmed records since the 2013–2014 season. Overall, 12 sites were confirmed occupied by Eastern Indigo Snakes and 7 sites were confirmed occupied by Eastern Diamond-backed Rattlesnakes.
From 2019–2022 (a complete rotation of all 60 survey sites), we conducted 179 surveys and observed 63 indigo snakes, 39 indigo snake shed skins, and 21 eastern diamondbacks. Indigo snakes were detected at 50% of potential overwintering sites, and the estimate for the total number of occupied sites increased to just over 60% when accounting for our ability to detect indigo snakes. In other words, some sites were likely occupied, but we failed to observe any indigo snakes over three surveys. Despite their large size, indigo snakes can be surprisingly hard to spot when cryptically basking in long grass. In some cases multiple observers have walked right by an indigo snake only for it to be spotted as it bolted for a nearby tortoise burrow. Furthermore, some surveys sites may not have any indigo snakes available to observe (i.e., they are underground or foraging offsite), despite the site being occupied at some point during the winter season. This is why it is important to visit all sites on multiple occasions and to account for detection when making inferences about indigo snake populations.
Indigo snake conservation continues to be a complex and challenging problem. Occupancy rates have remained relatively steady in recent years and extensive management efforts on properties throughout southern Georgia have unquestionably improved habitat quality on many sites. However, threats remain, including logging, road mortality, and continued decline of Gopher Tortoise populations on marginal sites. Understanding how these factors are impacting indigo snake populations will be a critical part of ongoing conservation efforts. Importantly, there has been a recent effort to expand this monitoring scheme to include sites in northern Florida, which would significantly increase the spatial coverage of indigo snake monitoring. Currently, it is difficult for U.S. Fish and Wildlife Service and other partners to make listing and status decisions about indigo snakes because of a lack of data in Florida. Expanded survey efforts will allow stakeholders to make these decisions using the best available information.
