Monitoring Eastern Indigos in Georgia

Monitoring
programs are a very important part of any natural resource program,
particularly wildlife conservation programs. The basic goal of any monitoring
program is to determine how some variable of interest changes over time. That
variable could be Indigo Snake population size, tortoise burrow density,
groundcover plant diversity, or hardwood shrub density. A well-designed
monitoring program can allow scientists and natural resource managers to
identify declines in an important variable before it is too late to reverse
that decline. Monitoring programs can also help identify the factors that might
be causing a decline (or an increase) in their variables of interest. Although
conceptually simple, creating an effective monitoring program can be very
challenging. Like a good research project, an effective monitoring program
requires careful thought and planning in order to determine which variables
should be monitored to help address conservation or management goals. These
variables need to be measured in a standardized way that is comparable across
years. Monitoring programs also require a long-term commitment, since many
years may pass before a change in a variable is detected.

The
Orianne Society recognizes the important role that monitoring plays in
conserving the Eastern Indigo Snake. As a result, we have initiated a
multi-level monitoring program in the Altamaha River Drainage that will allow
us to monitor the population status of the Eastern Indigo Snake in this region.
The Altamaha River Drainage is a stronghold for Eastern Indigo Snakes in
Georgia. Although the Eastern Indigo Snake appears secure within the Altamaha
River Drainage, this status could potentially change with changes to the
habitat from urban development, road construction, fire suppression, or
commercial forestry. Therefore, it is important to monitor the status of the
Eastern Indigo Snake in the Altamaha River Drainage so that any future declines
are promptly identified.

The
Orianne Society currently monitors Eastern Indigo Snakes in the Lower Altamaha
Drainage at two levels (or spatial scales). The first level encompasses the
Indigo Snake’s distribution within the entire Lower Altamaha Drainage, which
allows us to see how Indigo Snakes are doing at a regional level. Monitoring
across such a broad area creates some challenges. What variable could we
measure at a regional level that would reflect Indigo Snake population status
but would not require so much effort as to be cost-prohibitive? It turns out
that monitoring whether or not a species is present at particular site (also
called species occupancy) is a very useful indicator of population status and
can be measured with a very reasonable amount of effort. The Orianne Society
currently monitors Indigo Snake occupancy on 40 sites distributed across the
drainage on both public and private land.

The
second level of Indigo Snake monitoring occurs at a few key populations within
the Lower Altamaha Drainage, including the Orianne Indigo Snake Preserve
(OISP). At these key populations, we monitor Indigo Snakes through
mark-recapture. Mark-recapture involves marking as many individuals as possible
and then recapturing those individuals at a later date. We mark our Indigo
Snakes using small microchips called Passive Integrated Transponders, or PIT
tags. These tags work the same way an identification chip for a dog or cat
works and are placed just underneath scan. When we scan a marked Indigo Snake
with a special reader, we can record that snake’s unique identification number
and know when and where it was first marked. Done repeatedly over time, these
recapture data can be used to estimate survival rate, population size, and
population growth rate. Obviously, this requires much more effort than simply
surveying for Indigo Snake occupancy. However, our key populations represent
important populations on protected lands across the Drainage, making very
detailed monitoring of these populations worth the effort.

In
March 2012, we concluded the fourth year of mark-recapture monitoring and
second year of occupancy monitoring. We are currently planning to expand our
monitoring efforts at the OISP to monitor key habitat features that are
important to Indigo Snakes, such as tortoise burrow numbers and vegetation
structure. This will allow us to determine the success of our Land Management
practices in improving Indigo Snake habitat. The Orianne Society looks forward
to continuing our Indigo Snake monitoring program into the future and making
sure this species persists in perpetuity.