Guest Column: Gopher tortoises
Susan van Hoek
GTM Research Reserve Environmental Educator
According to the Florida Fish and Wildlife Commission, the gopher tortoise is the only land tortoise native to the United States, east of the Mississippi — its population is rapidly declining; they are listed as “threatened” in Florida and are candidates for federally “endangered” status.
Critical research shows that the gopher tortoise (Gopherus polyphemus) is falling victim to overharvesting, disease, loss of habitat from human encroachment and humans relocating them away from their preferred home base. Another threat is humans running over the lumbering tortoises as they attempt to cross roadways.
Their decline could present a greater problem because the gopher tortoise is a keystone species in the ecosystem in which they reside, meaning that their endangerment would likely have an adverse effect on other plants and animals within their natural communities.
The tortoise grazes on vegetation and thus disperses seeds that help the plant community thrive. They are also prolific diggers, burrowing as deep as 10 feet or more and laterally anywhere from 15 to 48 feet. These extensive burrows allow for a number of other species to drop in on their obliging hosts for a brief respite from predators or foul weather, while a few will stay for life. Research shows that over 350 or more commensal species have been recorded utilizing gopher tortoise burrows at one time or another.
“The burrow is particularly important as shelter for the endangered eastern indigo snake and two species of special concern, the Florida mouse, and the gopher frog,” says Jaime Pawelek, a biologist at the Guana Tolomato Matanzas National Estuarine Research Reserve.
Pawelek conducts research in coastal northeast Florida within the GTM Research Reserve. She is currently publishing a paper on gopher tortoise ecology in coastal habitats with Matthew E. Kimball. Kimball serves as both GTM Research Reserve’s Research Coordinator and University of North Florida Assistant Professor of Biology.
A GTM Research Reserve comprehensive survey of gopher tortoise burrows began in 2005 on the Guana peninsula, roughly 950 acres of upland mixed habitat. A second survey in 2007 included the Guana peninsula, as well as a 115-acre stretch of undeveloped coastal beach dunes. Researchers conducted a third survey in 2011 on both Guana peninsula and beach dunes.
Because gopher tortoises spend most of their time inside their burrows, they can be hard for the surveyors to find. Some even camouflage their digs under vegetation. To discover burrows, a team of researchers and volunteers systematically traverses the ground in search of an “apron,” a telltale mound made of excavated soil and sand in front of a burrow entrance. Once located, records are made of the burrow site via GPS. Other data collected includes tortoise class size (e.g. adult, sub-adult, or juvenile) and burrow status (active, inactive, or abandoned).
Results from the three surveys show burrow numbers remaining stable on the Guana peninsula and increasing on the beach dunes. While Pawelek says these numbers could possibly result from differences in survey efforts, she adds that they are hopeful that the increase is due to a growing population.
To monitor activity of burrow commensals, Pawelek recently set up motion activated cameras in front of both active and inactive adult burrows. She positioned each camera facing a burrow so that it records 30-second video clips whenever it detects animal movement. The system has recorded an Eastern coachwhip, Southern toad, and several mice and rats utilizing burrows. Mammals observed near entrances or going in and out of burrows include Virginia opossums, bobcats, armadillos, marsh rabbits and raccoons. To see video clips, visit the GTM Research Reserve’s YouTube channel.
Pawelek reports that data collected from the trail cameras show that all initially selected inactive burrows have either collapsed or become active again. She notes that, “Monitoring inactive burrows through the use of trail cameras has shown how quickly burrow status changes, thus stressing that these are very dynamic systems.”
To help rescue and rehabilitate the declining gopher tortoise population, researchers are not just looking at the burrows and who uses them. They gather facts concerning gopher tortoise habits: what they prefer to eat, where they reproduce and live, how much terrain an individual stakes out as their own territory and how they manage to keep rivals at bay.
Published and pooled data will help provide a more thorough picture of the overall needs of the gopher tortoise. Pawelek believes that by monitoring the Reserve’s tortoises over time, management decisions can be influenced to better protect and improve their habitat, which not only benefits the tortoises, but their burrow commensals as well.
The public is generally not aware that as the law stands it is illegal to damage a gopher tortoise burrow. Permits are required to move gopher tortoises from their home territory for clearing land or for development, in which case the law states, “The gopher tortoise must be protected, or relocated to a safer area.” The only exception to needing a permit is for wildlife management to improve habitat.
Anyone seeing an injured gopher tortoise or any other wildlife species in trouble should report it to the Florida FWC Hotline at (888) 404-3922.