Desert Tortoise: Hot! Hot! Hot!

A desert tortoise seeks shade in a man-made burrow.

Summer months are the best times for people to get out and enjoy the great outdoors, to go swimming, or to just to relax, but for the desert tortoise, it is time to get some much-needed rest. For most animals the summer season is the time to be productive in life by gathering food, finding a mate, or even establishing a home territory. But the Mojave Desert’s summers are harsh, making it difficult to be active with temperatures reaching well above 105 degrees Fahrenheit (41 degrees Celsius) and with very little (if any) rain. The desert tortoise is well adapted to deal with such extreme weather by going into estivation during the extreme heat of the summer.

Estivation (from the Latin word aestas, meaning summer) is a state of summer dormancy similar to winter hibernation, but in summer estivation, tortoises don’t sleep all the time. In most instances, the tortoises are active for a few hours during the morning and retreat back to a favorite burrow to sleep through the day. As dusk approaches, the tortoise  leaves the burrow for a few hours to eat or drink before night falls. In some cases if there are cooler days or even monsoonal rains, the tortoises come out of their burrows to take advantage of the rain and cooler temperatures. But during the months of June through the end of September, desert tortoises mostly remain inside their favorite burrows for summer sleep so as not to use up energy unnecessarily.

Desert tortoise hatchlings at the entrance to several burrows

We are currently conducting an experiment at the Desert Tortoise Conservation Center that may benefit the well being of the desert tortoises on site. We are doing a burrow temperature study that will help determine if the artificial burrows we dig for tortoises maintain the same temperatures as burrows that tortoises dig themselves. Since tortoises spend 95 percent of their lives in burrows, this is very important information for us to know! We placed temperature data loggers in both natural and artificial burrows and set them to record temperature throughout the day.

By analyzing the temperatures in both artificial and natural burrows, we will find out if we need to change the way we dig the artificial burrows so that tortoises can comfortably estivate in summer and hibernate in winter. If temperatures are too high inside the burrow, the tortoise living inside it can get very sick, or even die, so we want to make sure that every burrow we dig provides them with all the protection they need from the harsh heat of the Mojave summer.

Daniel Essary is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center. Read his previous post, A Long Winter’s Sleep.

3 Responses to Desert Tortoise: Hot! Hot! Hot!

  1. Daniel… thanks for posting. I love reading about the tortoises. Once you have your data, please share!

  2. Daniel,
    Would love to communicate direct with you. I have a lot of data on burrow temps. If that is PVC (hatchlings), it will conduct heat in due direct esposure to sunshine (no shade of plants over burrow entrance and not provide the snugness of a natural burrow for temp stability.
    Also leaches formaldehyde , possibly PBA and ptylates as well as not breathing.
    Larger tort in burrow has no snugness for temp stability, same issue as with dog loos, etc.
    Thank you for caring about my shelled friends and would love to see you data when finished. Are you also measuring ambient humidity vs. burrow humidity?
    Just a couple of cents worth.

    Moderator’s note: Your comment has been forwarded to Daniel.

    • Thanks so much for your comments and interest. We use roofing tiles for our hatchling burrows and PVC for adults. We never recommend that anyone use PVC for permanent burrows for their pet tortoises at home due to the issues you described, but we have not found another material for our temporary burrows that we can easily pull up and disinfect every few weeks as tortoises move to other enclosures. We have strict biosecurity protocols that require us to disinfect or sterilize every material that comes into contact with a tortoise before it touches another tortoise, so this is a key aspect of determining which materials we use for burrows. All of our burrows are covered under several feet of soil, so none are exposed to sunlight, and we use a variety of sizes to best accommodate tortoises’ sizes, but they will never be as perfect a fit as a natural burrow. We are also measuring humidity with our data loggers. It would be great if you could direct us to literature that measured the leaching of formaldehyde, PBA, and ptylates from PVC, and if you could make suggestions for other materials we could use for burrows because we always want to do what’s best for these animals. Thank you!