Tracking Indigos in Unusual Landscapes

For
those of you who are familiar with the ecology of Eastern Indigo Snakes, you
probably know that Indigo Snakes require large tracts of natural habitat in
order to maintain viable populations. These large expanses of natural habitat
were historically present throughout the Longleaf Pine ecosystem that covers
southern Georgia and most of Florida. This ecosystem included dry, open
sandhills that supported large numbers of Gopher Tortoise burrows and provided
overwintering habitat for Indigo Snakes. During the warmer months, from May
through October, Indigo Snakes had an extensive choice of habitats in which to
forage; moist flatwoods carpeted with saw palmettos, bottomland floodplain
forests interspersed with sloughs and oxbow lakes, or isolated wetlands
bordered by cypress or perhaps open marshes. The loss, fragmentation, and
degradation of these natural habitats are one of the greatest threats to Indigo
Snakes today. Areas in southern Georgia and Florida that still contain large
tracts of these different habitat types are the places that currently support
some the largest and most intact Indigo Snake populations.

So
why was it that I found myself tracking an Indigo Snake through a cow pasture
with my field technician, Zach Forsburg? We were in Highlands County, Florida,
north of the town of Lake Placid, following an Indigo Snake that was implanted
with a radio transmitter. Based on its movements, the snake did not seem to
mind living in a disturbed landscape. He was captured at a Gopher Tortoise
burrow in an old field that was formerly a citrus grove and was now residing on
a neighboring cattle ranch. Although this ranch does contain some natural
habitats, such as cabbage palmetto-oak hammocks, most of the ranch was actively
grazed with various degrees of disturbance. This did not seem to bother “Max.”
That day we were fortunate enough to find Max on the surface crawling through
an open pasture near a small brush pile. As we captured him to weigh him and ensure
that he is still healthy and feeding, I looked around and wondered; how is it
that a species normally associated with large swathes of intact Longleaf Pine
is able to persist in a landscape not normally associated with large, native
wildlife?

It
turns out that this phenomenon is widespread among Indigo Snakes in southern
Florida. Although Indigo Snakes are in fact found in large natural areas, such
as the Archbold Biological Station in Highlands County, Indigo Snakes are also commonly
reported in non-natural habitats such as cattle ranches, suburban developments,
rural communities, abandoned citrus groves, even along canal banks in sugar
cane fields!

What
is it about these habitats that bring in the Indigo Snakes?

Part
of the answer may come from Florida’s mild climate. In southern Georgia and
northern Florida, Indigo Snakes require Gopher Tortoise burrows for shelter
from cool winter temperatures. As one moves further south, this requirement
becomes increasingly lax. Researchers near the Kennedy Space Center in Brevard
County, Florida, have radio-tracked Indigo Snakes that were never observed to
use tortoise burrows but instead used other shelter sites, such as brush piles,
root holes, or armadillo burrows. In extreme south Florida, Indigo Snakes can
occur along the edges of mangrove swamps and use crevices in the limestone as
refugia. With fewer restrictions on what makes good refugia, Indigo Snakes can
use a greater diversity of habitat types.

Many
of these non-natural landscapes also provide an abundance of prey, particularly
those near agricultural habitats. For example, Indigo Snakes living along
canals in abandoned citrus groves or sugar cane fields have a diverse buffet of
water snakes, frogs, and small mammals living in and along the canals. These
canals are also riddled with potential refugia in the form of small mammal
burrows or old irrigation pipes.

Cattle
ranches in south Florida are probably more important to Indigo Snake
conservation than their usage may suggest. Although most ranches do contain
some disturbed pasture habitat, many still contain an amazing amount of natural
habitats including scrub, flatwoods, bayheads, hammocks, and wetlands. Private
ranches are actually very important for the conservation of other large,
wide-ranging predators in Florida, like black bear and the endangered Florida panther,
by providing large tracts of natural or lightly disturbed habitat that is
protected from development and fragmentation. I have had the chance to see some
very beautiful ranches in Highlands County; some which make you think you are
in some pristine protected preserve. Our ongoing radio telemetry research in
Highlands County is showing that Indigo Snakes will readily use ranches.

The
ability of Indigo Snakes in south Florida to use a diverse range of habitats is
encouraging as The Orianne Society and our partners work to conserve this
species. However, simply finding Indigo Snakes in a suburban development or
along a canal bank does not necessarily mean that those snakes represent a viable
population that will persist into the future. Indigo Snakes living in
landscapes, natural or non-natural, that contain a high number of roads are at increased
risk from road mortality and these mortalities could jeopardize the viability
of those populations. Non-natural landscapes often have more human activity
which could put snakes at risk from direct human persecution. Even with their
federally protected status, people may still try to kill Indigo Snakes.

When
the number of snakes getting killed due to natural mortality (like predation)
and human-influenced mortality exceeds the number of snakes being born, the
population will start to decline. In conservation biology, we refer to those
populations as sinks. Population sinks may persist for many years, especially
if they recruit individuals from a nearby source population, but if this
recruitment ceases, the population will become extinct. The Orianne Society is
planning to study the population viability of Indigo Snakes in non-natural
landscapes of southern Florida using data from our Highlands County study, as
well as data collected by other Indigo Snake researchers, to determine if these
landscapes can support viable Indigo Snake populations. Determining if Indigo
Snake populations in non-natural landscapes are viable and whether they will
persist into the future are questions that must be answered before we can
determine the value of non-natural landscapes to Indigo Snake conservation in
south Florida.