Kiley BriggsViews:
Gopherus berlandieri: The Lesser-known North American Tortoise
There is no doubt that Gopher Tortoises play an important role in sandhill ecosystems through much of the southeast coastal plains. Hundreds of other species use Gopher Tortoise burrows for one reason or another, and the burrows provide shelter to many of those species during fires. Some, such as the Eastern Indigo Snake, depend on the burrows to survive the winter. Likewise, in the desert southwest, two species of Desert Tortoise (Sonoran and Mojave) are also considered keystone species, meaning they alter the environment or food web in such a way that the landscape would be very different without them. In addition to digging burrows, these tortoises help cacti and other plants by spreading and fertilizing seeds after they eat fruit, and of course, eventually poop. Gopher and Desert Tortoises are fairly well known, but a fourth tortoise species native to the United States flies much more under the radar; the Texas Tortoise.
Examples of Tamaulipan thornscrub and how the Texas Tortoise uses the dense shrubs as as shelter.
Found through most of South Texas and across the border into the Mexican states of Coahuila, Nuevo Leon, and Tamaulipas, the Texas Tortoise differs from other North American tortoises in a few ways. For starters, they top off around 9 inches in length, much smaller than the others. Their skin and domed shells can be somewhat variable in pattern and color, usually some mix of gray or tan. Juveniles and some adults may also have large yellow spots in the center of each scute (armored plate) on their shells. Most of the Texas Tortoises I encountered had a very weathered appearance, and many had scars from past injuries or fungal infections; testaments of hardships the tortoises endure living in a rugged environment alongside humans and our machines.
Scroll through the above images to see how the Texas Tortoise uses prickly pear cactus as protection from heat and predators.
During my time at The University of Texas Rio Grande Valley, I was lucky enough to study how Texas Tortoises use the landscape and spent countless hours crawling through dense thornscrub in search of these secretive animals. When I say “crawl”, I really mean it. In much of the Lower Rio Grande Valley, Tamaulipan thornscrub comprises some of the best habitat for the species, but thornscrub can be quite difficult to traverse. Very dry and sandy, and with nearly every shrub covered top to bottom in thorns, Tamaulipan thornscrub is described in textbooks as being formed of impenetrable thickets of dense shrubby vegetation. Yet, determined to observe the Texas Tortoise in the core of its habitat, penetrate these thickets I did, several times losing the shirt off my back in the process. Interspersed within those thickets, patches of more open habitat are great places to find wildflowers and prickly pear cactus, the latter of which the turtles also use as shelter. The cacti and dense thorny shrubs work so well as protection from predators that the Texas Tortoise has abandoned a trait that is nearly ubiquitous with its North American relatives. They almost never dig burrows.
Some Texas Tortoises have distinct yellow blotches in the center of each scute, caused by the tortoise darkening as it ages.
Rather than burrow, Texas Tortoises tuck themselves into the base of shrubs, shelter under grass tussocks, bulldoze their way into woodrat nests, or wedge themselves under prickly pear cacti to avoid predators and extreme heat. While jammed deep within a cactus or an extremely prickly shrub, these tortoises are nearly as protected from predators as a Gopher Tortoise is at the bottom of a 25-foot long burrow. However, while other tortoises lay their eggs near the opening of their burrows, Texas Tortoises sometimes travel outside of their home ranges to nest, up to several miles. Wherever they nest, they only lay 1-3 eggs per clutch, less than half that of the other North American tortoises, and they may spread their eggs out by laying each egg in its own nest.
Rather than dig burrows, the Texas Tortoise shelters under dense shrubs, at the base of trees, under cacti, or inside rat nests to avoid predators and extreme heat.
Considered Threatened in Texas, the smallest North American tortoise faces a tough road ahead, literally. Although their home ranges are fairly small, sometimes only half an acre, many are killed on roads, even those with minimal traffic. In places where invasive species of grass have overrun the habitat, the turtles spend considerable time walking and foraging along roads, putting them at greater risk of being crushed by cars or mowing equipment. Meanwhile, much of their habitat is being lost to development and intensive agriculture, and many tortoises are unlawfully collected as pets. If they can avoid these growing threats, however, a Texas Tortoise might live easily into their 50s or more, but their potential lifespan remains a mystery.
Tortoises that survive being hit by cars or injured by mowers will carry scars on their shells for the rest of their lives, many decades in some cases.
Although I have not seen once since I left Texas six years ago, the Texas Tortoise is a species I will always hold in high regard. Spending two years in the field with these remarkable animals brought me to some of the most rugged, beautiful, and remote settings the lower Rio Grande Valley has to offer. Not every moment I spent with the tortoises was enjoyable, a fact I was reminded of recently when I removed a thorn that had embedded itself in my leg during a tortoise survey nearly seven years ago. However, the features that make Tamaulipan thornscrub a challenging environment for biologist to work in are the same features that the Texas Tortoise relies on for protection. Ultimately, the future of the Texas Tortoise depends on the protection and restoration of its habitat.
