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with Steven Whitfield PhD, Dr. Steven Whitfield is a wildlife biologist and Conservation and Research Specialist at Zoo Miami
The Gopher Tortoise (Gopherus polyphemus) is the only species of tortoise native to Florida, and is a threatened species within the state. Gopher tortoises were formerly more widespread in Miami-Dade County, but early settlers hunted them for food and dramatically impacted populations. In recent decades and even today, gopher tortoise populations are dramatically impacted by habitat loss from urban development. The Pine Rockland reserve surrounding Zoo Miami supports a population of gopher tortoises - one of the southern-most populations within its range, and a population entirely surrounded by urban environments. Miami is the warmest and most urban part of the range of the gopher tortoises, but all of Florida is warming because of greenhouse gases and many parts of Florida are becoming more developed as the human population expands. Consequently, Miami’s gopher tortoises offer insight into conservation of tortoises of the future.
Our gopher tortoise program at Zoo Miami is focused on the biology and conservation of gopher tortoises in Miami-Dade County, and is focused on education of zoo guests about the biology and conservation of tortoises.
Numbers, reproduction, and growth rates
Our most basic research with tortoises is trying to understand how many there are in Miami-Dade County, and how quickly they reproduce and grow. We’ve been conducting surveys of tortoise habitats for several years in county preserves throughout Miami-Dade. During the breeding season, we take x-rays of female tortoises, which allows us to count the number of eggs they produce each year. We mark each tortoise individually, and measure our tortoises regular so we can estimate growth rates. There are probably less than 200 tortoises in all of Miami-Dade County, but because of our warm weather we’re learning that tortoises here lay more eggs than usual, and growth rates appear to be higher than normal - which is a good sign for the tortoise’s potential to recover.
How much space do tortoises need?
Understanding how much space an animal needs is one of the most basic requirements for conservation. We’re conducting a study using radio telemetry to understand the movement patterns and home range size for gopher tortoises in the pine rocklands. This will allow us to better understand how much space each tortoise needs, what types of habitats tortoises like best, and helps us understand how tortoises are interacting socially.
Pine rocklands are a rather unusual habitat for tortoises, since most pine rockland areas have very little soil for tortoises to dig in for their burrows. Further, the tortoises need habitats where sunlight hits the ground so they can bask in the sun. Yet in the pine rocklands, sunlight only penetrates to the ground when the ecosystem burns regularly, and one of the management challenges for pine rocklands is that humans have long suppressed the wildfires that are part of the natural ecology of the rocklands. We’re conducting a study of habitat associations of gopher tortoises where we sample dozens of habitat variables of sites where tortoises have made burrows so that we can better plan for habitat management for the tortoises.
We use small temperature recorders attached directly to the tortoises’ shells to record fine-scale temperature data on the tortoises. Information collected in this study will help understand the temperature preferences of tortoises in different habitats, helps us understand how tortoises respond to record-breaking heat waves, and in the case of this week, how tortoises deal with cold weather. The whole process for the tortoises takes just a few minutes, and then they’re released back into their homes in the pine rocklands.
Which species use tortoise burrows?
Gopher Tortoises are very important for their ecosystems. They create deep burrows that are used by many other species of wildlife - including mammals, reptiles, amphibians, and insects. Conservation Intern Daniel Valle from Florida International University has been using automated camera traps to study tortoise behavior in the pine rocklands surrounding the zoo. Camera trap videos show interaction among tortoises - including frequency of foraging away from burrows, courtship and mating, and aggressive interactions among tortoises. Camera trap videos also show that many other species of animals in the pine rocklands use tortoise burrows, including snakes like Black Racers and Coachwhips, and small mammals like Hispid Cotton Rats, Black Rats, and Eastern Cottontails.
How do tortoises affect plant communities?
Gopher tortoises are important not only for animal communities in the ecosystems where they live, but are important to the plants as well. Adrian Figueroa from Florida International University began conducting a research study of seed dispersal by gopher tortoises while a conservation intern at Zoo Miami, and is now continuing his research as a PhD student. We’re learning that tortoises eat a range of native and non-native plant species, and can affect germination rates of these plants as well as their distribution in the ecosystem. Adrian has been identifying seeds that tortoises eat, and is now beginning germination trials to determine how a tortoise digestive system impacts survival of the seeds.
A save haven for lost tortoises
In 2019, Zoo Miami partnered with Miami-Dade County’s Natural Areas Management and Environmentally Endangered Land program and FWC to create a home for tortoises that were displaced by people and can’t return to their own homes. This site for “waif tortoises” allows us to monitor tortoises to make sure that they are adjusting well to their new homes. Because tortoises are so important for the ecosystem and the species, protecting the tortoises will help protect the entire community of animals that use tortoise burrows.
Tortoise health and Upper Respiratory Tract Disease
One of the major threats to tortoise populations in the southeast is an emerging disease called Upper Respiratory Tract Disease (URTD), caused by two species of bacteria in the genus Mycoplasma. We’re conducting tests of tortoises found throughout Miami-Dade County to determine if they’re healthy, and if they’ve been exposed to the bacteria that can cause the URTD.
Thanks to a grant from the Gopher Tortoise Council’s Donna Heinrich Environmental Education Fund, Dr. Steven Whitfield teamed up with Zoo Miami Foundation’s Conservation Teen Scientist program to help train high school students to serve as advocates for tortoise conservation. Students learn about gopher tortoises, and go to the field with Dr. Whitfield to get first-hand experience working with the tortoises. Students then help teach zoo visitors about tortoises using one of the tortoises from Zoo Miami’s Critter Connection.
Florida’s Fish and Wildlife Conservation Commission has a state-wide campaign called Gopher Tortoise Day for tortoise education and outreach, on April 10th of each year. In 2019, Zoo Miami hosted its first Gopher Tortoise Day event - with a crawl-in tortoise burrow for kids, an ambassador tortoise for guests to meet, and with educational information for all guests. If you’re interested in getting involved with Gopher Tortoise Day or hosting your own tortoise event, please check here.
Have you seen a gopher tortoise or its burrow? You can help the Florida Fish and Wildlife Conservation Commission by using their new app to snap a pic and report sightings. Download the Gopher Tortoise app here and help biologists map out Florida’s populations.
Have you seen one of our research tortoises? They are occasionally displaced by people and need to find their way back to their burrows. If you’ve seen a tortoise in Miami-Dade County that’s wearing some tech like a radio transmitter or has numbers painted on its shell with non-toxic paint, please call the zoo at 305-251-0400.
For media coverage of this program, check out these links:
FAU University Press Feb 19, 2019
Herpetological Review Feb 2018
National Geographic Apr 10, 2017