The best chance for survival.
The goal of our Reintroduction Program is to reestablish extirpated populations — bringing the species back to the wild where they once existed.
Establishing viable Eastern Indigo Snake populations through reintroduction is challenging because repatriations are faced with all the limitations that small populations experience. In order to mitigate these limitations, we have focused on three areas of consideration when designing the reintroduction program: release site selection, release strategy and release site monitoring.
RELEASE SITE SELECTION
When determining reintroduction sites, we asked ourselves the following questions:
- What factors caused Eastern Indigo Snakes (Drymarchon couperi) to decline initially, and can we mitigate these factors?
It is important to determine what caused the original decline at a potential release site prior to reintroduction and to determine if those factors can be mitigated enough that they will not negatively affect reintroduced populations.
- Can the site be restored, and will it be managed long-term?
Good quality habitat at the reintroduction site is critical for success. If the habitat is too far degraded and cannot be restored and managed long-term, it cannot support a healthy population of Gopher Tortoises (Gopherus polyphemus) and Eastern Indigo Snakes.
- Is the reintroduction site large enough to support Eastern Indigo Snake populations, and is there connectivity to additional sites?
Little is known about the spatial population structure and ecology of Eastern Indigo Snake populations. Specifically, the minimum size of habitat patches required to maintain a viable population, and the habitat components that are required to maintain connectivity among populations. However, there are studies that suggest that individual animals require large protected areas that contain a diversity of habitat types.
- Are there Eastern Indigo Snakes already occurring at the site?
We are currently interested in reintroduction efforts and not augmenting existing populations, so it is important to know if Eastern Indigo Snake populations currently occur at potential reintroduction sites. Though there have been no recent sightings of Eastern Indigo Snakes in the Panhandle region since the late 1990s, this species can be difficult to find in the wild, and further surveys are required before repatriation efforts begin.
- Who are the partners involved, and are they dedicated to reintroduction efforts?
One of the most critical issues to the success of repatriation efforts will be establishing and maintaining partnerships with a variety of agencies, organizations and private individuals. Specifically, it is important to work closely with permitting agencies and entities that own release sites.
The strategies used to release animals can have a significant effect on success. When considering how to release Eastern Indigo Snakes, we are considering how many should be released per site, snake age and size, timing of release, sex ratios, snake health, genetics and imprinting on seasonal habitats. The following specific guidelines may be adjusted based on conditions at release sites or the experimental model for different release sites:
- Quantity Released. We plan to release approximately 30 Eastern Indigo Snakes per year at each release site. We plan to continue releasing snakes at this rate until we determine that the release sites are reaching carrying capacity.
- Age and Size. We will raise Eastern Indigo Snakes in captivity for approximately one and a half years, at which time they will be released into soft release enclosures. Snakes will be released from enclosures when they are approximately two years old and should be able to accommodate PIT-tag placement and transmitter implantation. We also may experiment to determine if we could have greater success by releasing snakes that are one, one and a half, or two years old.
- Sex. A sex ratio of 1:1 would be ideal in establishing each new population. Some studies have found a ratio of 2:1, males to females in wild populations. In some situations, we may release female-biased sex ratios to increase the number of reproductive females in the population and thus increase the probability of productive nests.
- Health Assessments. Pre-release screening of each snake is critical to the success of the individuals released and for the preemption of disease vectoring into wild populations of reptiles. Testing and screening prior to release in repatriation areas will be similar to the procedures for snakes entering quarantine at the Orianne Center for Indigo Conservation.
- Genetic Considerations. Preliminary evidence using mitochondrial DNA suggests that an Atlantic clade and Gulf clade of Eastern Indigo Snakes exist. However, the patterns need to be further assessed using microsatellite markers. If there is indeed significant differentiation between clades, we will use animals from the Gulf clade to reestablish populations in the Panhandle region.
- Imprinting on Seasonal Habitats. We will release snakes during their second winter into soft release enclosures that have an abundance of overwintering habitat. Conservation biologists currently promote a “soft release” scenario for reintroduction programs. This requires the release of an animal first into an enclosure at the release site for a period of time so it may acclimate to the site, prior to release into the wild. This period in which snakes are maintained in the soft release enclosure provides for an orientation period and may reduce stress factors associated with adapting to a new environment.
RELEASE SITE MONITORING
Reintroduction sites for Eastern Indigo Snakes will be monitored annually to determine continued presence, relative abundance, survival, and whether reproduction and recruitment is occurring. Implementing a monitoring program will allow us to use an adaptive approach to increase success. Snakes will continue to be released at sites until it is determined the site is reaching carrying capacity as evidence by successful reproduction, high rates of emigration from the release site and stabilizing abundance estimates. Snakes will continue to be monitored after releases are ceased to determine if the population is sustainable without continued releases.
In the initial years of releases, a subsample of snakes will also be tracked using radio telemetry. Telemetry studies will help us monitor individual snake responses to release. For example, it will help us determine if snakes are imprinting on overwintering sites and if they are making movements considered typical for Eastern Indigo Snakes.