Gopher Tortoise Ecology in Pine Rockland

Gopher Tortoise Ecology ...

Gopher Tortoise Ecology in Pine Rockland

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.

Gopher Tortoises in the Pine Rocklands

Population recovery, babies, and growing up!

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 regularly 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.

Measuring a baby gopher tortoise

X-rays showing eggs
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.

Making a happy home

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.

Getting some sun!

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 us understand the temperature preferences of tortoises in different habitats, how they respond to record-breaking heat waves, and how they 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.

Why are gopher tortoises important?

Burrows Buddies

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. 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.

Forest Gardeners

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.

Saving Urban Tortoises

A Safe 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

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.

Gopher Tortoise Environmental Education

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 learned about gopher tortoises and went to the field with Dr. Whitfield to get first-hand experience working with the tortoises.  Students then helped teach zoo visitors about tortoises using one of the ambassador 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 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.

see a tortoise? report it!

Have you seen a gopher tortoise or its burrow? You can help the Florida Fish and Wildlife Conservation Commission by going to their website! Snap a pic and report sightings online here.

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

New research by Zoo Miami studies Miami's last endangered gopher tortoises

Gopher Tortoises are a threatened species that lives throughout pine forests of Florida, where they dig deep burrows to use as their homes. The leading threat to gopher tortoises in Florida is human expansion of cities and suburbs, which displace the tortoises and destroy the burrows they create. Given the extent of urbanization in Miami, it's not a surprise that the tortoises are rare here.

A new study led by Zoo Miami's Conservation and Research Department focuses on the last populations of gopher tortoises left in Miami-Dade County. One population is within the Richmond pine rocklands (surrounding Zoo Miami), and another at the Deering Estate. 

The study compared habitat features at tortoise burrows and random points in pine rockland habitat to assess the habitat requirements in pine rocklands. The pine rocklands are a habitat unique to Miami-Dade County, and are an unusual habitat for the tortoise because tortoises generally prefer sandy soils over rocky limestone soils. However, the team found that the tortoises are able to find sandy patches in the rocky soils to dig their burrows. In addition to deep sandy pockets, the tortoises require open canopy habitats with little leaf litter. Land managers can't effectively create deeper or sandier soil, but they can target areas with deep soils for prescribed burns - a management strategy that lowers canopy cover and litter depth.

"Gopher Tortoises in Miami-Dade County are at the forefront of threats from urbanization and warming climate," says Dr. Steven Whitfield, a conservation biologist at Zoo Miami who leads the gopher tortoise research. "We were concerned that the geology of the pine rocklands may also be difficult for the tortoises, but it's good to see that they don't seem troubled by rocky soils."

Gopher tortoises are known as a keystone species, a species that is critical to the function of habitats where they live. "More than 400 species of animals have been seen using the burrows created by gopher tortoises. Humans could learn a lot from them about how to coexist with other species," says Dr. Whitfield.

Ongoing conservation research is focused on developing management strategies for tortoises in areas encroached by urbanization, and on understanding impacts of warming climate on the tortoises.

If you see a gopher tortoise in or around Miami, you can help by reporting it to FWC's gopher tortoise reporting website

The study was published in the journal Ichthyology and Herpetology. 

Burrow Characteristics and Habitat Associations of Gopher Tortoises in Urban Pine Rockland Reserves (Miami, Florida, USA)

Steven M. Whitfield, Daniel Valle, Adrian Figueroa, Brianna Chin, Hugo Bravo-Gallegos, Frank Leone

Ichthyology & Herpetology 110 (1), 22-32. https://doi.org/10.1643/h2020168

Posted by Frank Ridgley at 06:30