tracking desert tortoises


Tortoise Tales: Tracking Desert Tortoises

Lindsey poses with a desert tortoise in the Mojave Desert.

We translocated a group of desert tortoises from the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC) into the wild Mojave Desert and followed them to study their movements post-release (see Spring Desert Tortoise Translocation).  My days started at 5 a.m. at the release site out in the desert. There are six separate sites that our tortoises reside in, and it was my job to locate every one of these tortoises every week. While working on this project, I saw some interesting things in the desert!

Immediately after translocation, the tortoises began to move around looking for their new homes. A small group took an especially long journey to the corner of the site, all at least a kilometer (0.6 miles) away from each other and from any other study tortoise. One resident tortoise living in this area joined our study, so we were able compare her movements as a normal wild tortoise to those of the tortoises we translocated. I nicknamed her Mrs. Rogers, because she was the only resident tortoise in a whole neighborhood of translocated tortoise friends. This site from then on was known as Mrs. Rogers’ neighborhood. In the future, we hope a male tortoise will take on the role of Mr. Rogers to help increase the population!

Lindsey uses tracking equipment to help find translocated desert tortoises.

I ran into a bit of luck one day while tracking a resident tortoise in another area. When I finally located her, I saw that she was flipped on her back, unable to right herself.  Was this due to a scuffle with another tortoise or a run-in with a predator? Because of the unique anatomy of a tortoise, death can occur if a tortoise remains on its back for an extended period of time because it is vulnerable to dehydrating and overheating if unable to seek shelter during the hottest parts of the day. I immediately righted the tortoise, wondering if I was too late. Fortunately, she walked away, seemingly unharmed.  A month after that incident, that resident tortoise is still doing great!

Sometimes, tracking tortoises can be a tricky job. Change in elevation, tortoise movement, and other obstacles make it difficult to get a good signal on our equipment. Sometimes, though, the tortoises make it easy. As I drove down the desert road, I was listening for one tortoise when I saw another study tortoise walking across my path. At first I was pretty excited, because this was one less animal I had to search for, but then I noticed he was missing his GPS unit, which we attached to him before he was released. The GPS units are only programmed to emit a signal for a certain period of time, and at that moment I only had about five minutes to locate it before the signal stopped. I quickly entered the GPS frequency and began searching for the unit. I finally found the missing unit in the mouth of a nearby burrow only a moment after the beeping stopped. The unit was recharged and reprogrammed and put back on the tortoise shortly after.

One afternoon I was tracking a group of tortoises in a wash, and I found something none of us had yet come across. There were several broken eggs in the dirt surrounding the caliche cave where one of my tortoises was living. Unfortunately, a predator attacked this clutch before hatching, but under good environmental conditions a tortoise may produce two clutches per year, so maybe next time we will see some hatchlings!

This badger was found in a desert tortoise burrow.

It is not unusual to come across a tortoise digging a soil burrow while tracking our study animals. One morning I was approaching a burrow in a wash, and I saw dirt flying out of it. As I got closer I came face to face with an American badger staring at me from the entrance of the burrow. I was getting an extremely strong signal from the burrow, indicating the tortoise that I was looking for was inside!  Badgers are carnivorous and are known to prey on tortoises, so I was concerned for the well-being of our study tortoise. I sat down several meters away to fill out my data sheet, which took several minutes.  I got up to leave and walked over to the burrow to take one last look. Our tortoise was looking right back at me! I guess the badger and tortoise are just two friends sharing a burrow.

My summer as a telemetry technician was filled with ups and downs: hiking, pulling cactus spines out of my legs, amazing wildlife, and awkward tan lines. Now, at the end of the summer, I can say the tortoises are all doing well and have somewhat settled down into homes throughout the site. They are interesting little creatures, and I hope the work we did and the data we documented will help make future projects a success!

Lindsey Perry was a seasonal research assistant at the San Diego Zoo’s Desert Tortoise Conservation Center. Thank you, Lindsey!


Desert Tortoise: Twizzler

Twizzler has a severe deformity caused by epoxy that was left on his shell when he was very young.

Twizzler has a severe deformity caused by epoxy that was left on his shell when he was very young.

Here at the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC) in Las Vegas, we have a number of special-needs desert tortoises that serve as wonderful education animals, and each of us has our favorites. Mine is Twizzler. He arrived here at the DTCC in 2007, and when he arrived, we found that he had hardened gray material all over the left side of his carapace (top shell), causing a severe deformity.

None of us had seen such a thing before, but we guessed that he must have walked through a construction site when he was young and had cement dropped or poured on his back. The natural growth on his right side indicates that he was likely covered in the cement for about 10 years. It wasn’t until months after he was brought in that another tortoise biologist told us that he was certain it was some sort of epoxy, and we could pick it off. Well, we spent months picking and delicately using a high-speed rotary tool to remove the cement. Although we were able to free him from the epoxy, he will never return to a normal tortoise shape, and because of that, he cannot be released because he would not be able to survive in the wild.

Well, that’s not the end of the story; a researcher visiting the DTCC recently came into my office where she saw Twizzler and exclaimed, “I know that tortoise!” She said that back in the early ‘90s, there were scientists conducting research on wild hatchling and juvenile desert tortoises. The researchers would attach radio transmitters to the tortoises’ shells to track them using telemetry, and after the project was over or when they could no longer hear the signal, they would abandon the tortoises, sometimes without removing the epoxy that kept the transmitters attached! Since the epoxy covered a large portion of the shell, including the seams between the scutes (sections of the shell), the tortoises grew up with severe deformities, if they grew up at all.

It took two days of scrubbing to get the toxic paint and sparkly glue off this pet tortoise when she arrived at the DTCC.

It took two days of scrubbing to get the toxic paint and sparkly glue off this pet tortoise when she arrived at the DTCC.

The moral of the story is this: do not attach anything to a tortoise’s shell, especially if it touches the seams! And on that same note, never paint your tortoise. A tortoise’s shell is highly vascularized, meaning it is full of blood vessels, so toxins may be able to get into the bloodstream through small openings in the shell and along the seams where tortoises may have suffered even slight injuries in the past. Instead, if you want to easily identify your tortoise, use a nontoxic paint pen and write its name and your phone number on its shell so you will be able to get it back if it’s lost. And an even better option to prevent from losing your pet tortoise, although you won’t be able to see an identifier, is to have your tortoise microchipped just like you would microchip your dog or cat!

Paula Kahn is a conservation program manager for the San Diego Zoo’s Institute for Conservation Research. See a previous post from her staff, Desert Tortoises: Lucy and Ethel.