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A History of Reintroduction Efforts
The Eastern Indigo Snake (Drymarchon couperi) historically ranged from southern Florida northwards into southern Georgia and west into the Florida Panhandle, southern Alabama, and southern Mississippi. However, indigo snake populations in the western portion of the range were extirpated by the late 1990s or early 2000s, following widespread habitat destruction, loss of Gopher Tortoise populations, and collection for the pet trade. This left a large chunk of the potential range with no indigo snakes, despite improving habitat characteristics and management on many of the large public properties in this region.
Indigo snakes remain listed as threatened under the U.S. Endangered Species Act, in part because of the loss of snakes in the western portion of the range. A portion of the U.S. Fish and Wildlife Service’s recovery goals for indigo snakes focuses on maintaining viable populations across four regions to improve long-term resiliency of the species. One of those regions encompasses southern Mississippi, southern Alabama, and the Florida Panhandle, where there are no remaining populations. Thus, for recovery goals to be achieved, indigo snakes must be successfully reintroduced to the Panhandle region. Snakes are currently being released at one site in southern Alabama and one site in the Florida Panhandle. I have written previously about some of the history and challenges associated with these efforts — creating new populations is often one of the most challenging undertakings in wildlife conservation.
As the project enters its 16th year, there has been a push among partners to better understand the population demographics of snakes after release. Snakes are notoriously difficult to study, and the original release goal of 300 snakes is within sight. However, it remains unclear whether releasing 300 snakes is enough to create a self-sustaining population. Earlier this year, partners held a Structured Decision Making Workshop to discuss these issues and outline goals for the coming years.
Despite being a part of the Eastern Indigo Snake Reintroduction Committee (a group of partners that oversees the project) for almost 10 years, I had never attended a release event. With increased focus on this project, it seemed like a perfect time to travel to southern Alabama and experience a release firsthand.
Headstarting Snakes in Preparation for Release
There is a substantial amount of research demonstrating that survival in animals often increases with body size. Juveniles are frequently the most vulnerable life stage. In an effort to improve the survival of released snakes, individuals are headstarted for approximately two years prior to release. This time in captivity allows them to be released at a much larger size compared to a hatchling indigo snake.
Indigo snakes are bred at the Central Florida Zoo’s Orianne Center for Indigo Conservation (OCIC) near Orlando, Florida. Adult indigo snakes in the breeding colony are paired during the fall and winter, and gravid females lay eggs in the spring. Once eggs hatch, juvenile snakes are raised at the OCIC for several months. Some individuals are then transferred to partners at the Welaka National Fish Hatchery or Zoo Atlanta to finish the headstarting process. During the headstarting period, all individuals are routinely monitored, which includes tracking growth, screening for disease, and generally making sure snakes are healthy before release. Any health concerns are addressed by veterinary staff.
The Day Before Release
The day prior to release, headstarted indigo snakes are transported from their respective facilities to the release site. Snakes are then processed for a final time. Processing snakes involves collecting length and weight measurements, taking photographs of each individual’s unique head markings, and confirming each snake’s PIT tag number (a microchip implanted under the skin that is used to identify individuals). Uniquely marking all individuals allows us to track those that are recaptured after release, and taking head photographs provides a secondary means of identification. Snakes are weighed using a spring scale and measured via a squeeze box. This method places snakes into a box with a plexiglass top and foam bottom so that the individual’s body can be traced by drawing a line on the plexiglass. A string is then used to convert this line into a body length measurement.
While all of these procedures are relatively simple, it can take several hours to process all of the snakes being released. We had a large group of partners present to make the process quicker. The data collected just before release sets a baseline for any snakes that are recaptured as part of post-release monitoring efforts.
Release Day
On release day, snakes are transported to the release site in the morning, and releases are usually finished within a couple of hours. Releases are popular events, and many partners and volunteers typically come out to help with the release. This year, there were 44 headstarted indigo snakes to release in Alabama. Snakes were split into two groups and released at two locations a little over a mile from one another. One of the primary project goals is to establish snakes at multiple overwintering sites within the larger release site, increasing the potential area occupied by the reintroduced population and making them more resilient to potential threats. Release sites are characterized by patches of upland habitat that currently support Gopher Tortoise populations. Furthermore, sites are only considered if they have been, and will continue to be, appropriately managed (primarily through the application of prescribed fire). Reintroduction projects that do not adequately address existing habitat issues almost always fail.
The actual process of releasing snakes is straightforward. Each snake is released directly into a Gopher Tortoise burrow, which provides immediate shelter while snakes acclimate to their new environment. Just before being released, snakes have their PIT tags scanned a final time to confirm that we know exactly where each individual is being released. Most snakes waste little time crawling into the tortoise burrow, although some individuals are quick to come back out and begin to explore their surroundings.
Post-release Monitoring
Release day is the last time that we will see many of the indigo snakes involved in this project. Whether it’s from mortality, emigration from the release site, or just our inability to locate snakes reliably, it has proven difficult to find snakes after release. In an effort to improve post-release detection, a network of paired game cameras and remote PIT tag readers have been established at both release sites. These methods will contribute critical data that allows us to better document what is happening to the indigo snake population after the snakes are released.
What’s Next for the Reintroduction Project?
Deciding when to stop releases (because of success or failure) is one of the most challenging decisions for a reintroduction project. With this year’s release, we surpassed our initial goal of releasing 300 snakes in Alabama, and we will reach that goal in a few years in Florida. In total, we have released over 500 indigo snakes at these two sites. Releases will continue for the foreseeable future, and efforts are underway to document that populations are self-sustaining. This is the key metric that would indicate further releases of animals are not required to maintain indigo snakes on the landscape. There is also interest in initiating releases at a third site, but that would likely require enough confidence in success to stop releases at one of the current sites. Ultimately, these efforts must be successful to meet the recovery goals for indigo snakes in the Southeast.
The indigo snake reintroduction project is currently being supported by a U.S. Fish and Wildlife Service Recovery Challenge Grant. This project would not be possible without financial support and effort contributed by a large partnership, including state and federal agencies, universities, and NGOs. This project will return Eastern Indigo Snakes to their forests.
