Monday, November 27, 2017

When Tortoises Attack ---Guest Post---

    As a graduate student at Florida Atlantic University, I study the insects that live within gopher tortoise burrows. One method I use to collect insects is by digging a hole near tortoise burrows that insects fall into, called a pitfall trap, and bait it with something lots of insects find irresistible: gopher tortoise dung. Not exactly glamorous work, but I am interested in how the tortoises and their burrows influence what kinds of invertebrate species can persist in the area i.e., their biodiversity. So why do I care? Some species of insects provide dung removal services in the burrows, potentially benefiting tortoises by reducing parasite loads. These animals may have critical value to the gopher tortoise, yet we know very little about them. So here I am, setting insect traps and digging through dung.

    On one of my first trips to our field site, Carolyn, a fellow graduate student, pointed, “Gertrude’s burrow is over there.” Carolyn was introducing me to gopher tortoise number 159; a large female she nicknamed Grumpy Gertrude. As we approached the burrow, I saw a head emerge from the tunnel. With heavy feet, Gertrude bounded towards us, rapidly bobbing her head, a clear sign of aggression. She approached my ankles as if she wanted to push me back. We were obviously not welcome here.

    When approached by humans, most tortoises will retreat into their burrows or simply ignore us. My study site has a very high density of tortoises, nearly 100 tortoises in 23 acres, and is located in a high traffic suburban greenway, so it is reasonable to assume that they are fairly used to people. Indeed, Dr. Jon Moore, who began researching this field site over 17 years ago, says aggressive behavior is rare, but there are a few individual tortoises with a bad attitude, like Gertrude.

    I went into the field one evening to check my traps, and as I sat digging through dung, a tortoise came out of its burrow with the same aggressive stride as Grumpy Gertrude. “Gertrude?”, I questioned as I excitedly reached for my camera. I was excited because I hadn’t seen Gertrude in almost two months, around the time Hurricane Irma hit Florida. As the tortoise continued to approach me, I got a better look at the ID number on her shell. Number 43. This wasn’t Gertrude. Unexpectedly, she lunged at me, nearly ramming into my camera (check out the video below!)


    Head bobbing, ramming, and occasionally biting are common forms of communication used by gopher tortoises to signal aggression to predators as well as members of their own species. These aggressive behaviors are most often related to competition for resources, mating opportunities, and defense against predators. Based on my personal observations, it seems that Grumpy Gertrude and Number 43 are especially territorial, at least as compared to the majority of tortoises at my study site.

    Gopher tortoises have varying personalities and, as we observe more details of their daily lives, we are finding they even have social lives. These animals interact in complex social networks displaying a variety of different interactions. They form tightly-knit groups called cliques and may intentionally avoid nearby neighbors. On the other hand, some tortoises regularly travel relatively far distances to visit certain individuals that they prefer to spend time with. This may be particularly common for such a dense population like the one at our study site. You could make the case that it is a veritable gopher tortoise high school, and needless to say, Number 43 didn’t want me in her clique.

    These complex social behaviors have important implications for how we conserve gopher tortoises. One of the leading threats to gopher tortoise populations includes the reduction of suitable habitat as a result of human development. At times, animals are moved when their habitat is going to be developed, but successfully relocating tortoises is not as straightforward as just placing them in a new spot. If tortoises are simply released to a new site, they inevitably attempt to navigate their way to their original stomping grounds. As we’ve discussed here, tortoise social behavior can be surprisingly complex and raises lots of questions about what else can be learned about this important, sometimes grumpy, keystone species.

 About the Author

Amanda Cristina Hipps first began researching gopher tortoises during her undergraduate career at the University of North Florida. She is currently working on her M.S. in Biology at Florida Atlantic University, studying gopher tortoise ecology and conservation. Specifically, her thesis investigates burrow commensals in southeast Florida, primarily focusing on invertebrate animals, filling in the data gaps on their ecology and distribution.


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