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.
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.