Tracking desert tortoise in the Colorado Desert
The desert tortoise population is in steep decline — in some areas, the population has decreased by 90%. Each year, the Mojave Desert Land Trust heads out to areas of critical tortoise habitat looking for signs of hope for this threatened species.
By Jessica Graybill, Mojave Desert Land Trust Social Media Manager
Tortoise surveys are an exercise in concentration and in being present. Lined up at 10-meter intervals called transects, each member of the team keeps their eyes on the ground as they walk straight lines through 500 x 500 square meter plots.
This fall, the Mojave Desert Land Trust went to the Chuckwalla Bench in search of desert tortoise. MDLT manages over 4,000 acres here in conservation easements. The land is being protected and managed so special status species like the desert tortoise can prosper.
Determining the presence — or absence — of Gopherus agassizii (Agassiz’s desert tortoise) helps MDLT and the California Department of Fish and Wildlife understand the conditions and health of the tortoise populations and habitat. Due to habitat deterioration from increased development and raven predation, the population has decreased by 90% in some areas. While sightings of live tortoises are rare, MDLT’s surveys are valuable even when tortoises themselves are not found; presence of scat, burrows, and sightings of shell fragments all get reported. While in the field we also note the presence of other sensitive species such as the American badger, desert bighorn sheep, and the Mojave fringe-toed lizard as well as rare plants such as Munz’s cholla (Opuntia munzii), the tallest endemic cactus in California, and desert unicorn plant (Proboscidea althaeifolia).
Our goal is to provide data that will be used to benefit the conservation and recovery of Agassiz’s desert tortoise while also demonstrating how ecologically valuable land is.
So, how exactly do you spend a day tracking desert tortoise?
6:30 am — We pack up our vehicles and head out from MDLT headquarters in Joshua Tree.
11 am — Hopping out of the car at Coon Hollow Campground, I’m struck by the view of the surrounding mountains and charmed by the riparian wash running parallel to the campground, which is richly populated by palo verde, smoke tree, mesquite, and ironwood trees. We pitch our tents, set up camp and have a few moments to enjoy lunch and get to know each other before biological consultants Ed LaRue and Sharon Dougherty arrive. This husband-and-wife duo have worked in conservation since 1989. Together they formed Circle Mountain Biological Consultants in 1994, and have completed hundreds of biological surveys in the decades since — including focused surveys for Agassiz’s desert tortoise, burrowing owl, and other special-status species.
11:50 am — After brief introductions, we head out to our first plot, which is about an hour away from our campsite and down a series of bumpy dirt roads. The Little Chuckwalla Mountains loom on the horizon. Parked safely on the side of the road, we grab our GPS devices and walkie-talkies, head out for the far corner of the plot.
We walk in 10-meter transects through a square mile of desert. When we make it to the end of the transect, each team member moves over 70 meters and heads back the opposite direction until the entire plot has been covered. We search thoroughly in front and behind ourselves, under and through shrubs, moving as a unit at the same pace — and when someone finds something noteworthy, the entire team takes pause while Ed logs the coordinates and the details of what’s been found. If the find is especially exciting, we might briefly abandon our transect to check out the specimen but otherwise, we stay in our own lanes.
This plot was rife with tortoise signs, particularly scat, which can be incredibly difficult for an untrained eye to spot on the desert pavement. We also encountered a vacant burrow where we spotted an eggshell fragment. I would have assumed it was from a bird, but the proximity of the tortoise burrow and the curvature of the shell indicated that it was indeed a tortoise egg.
In Chuckwalla there’s a lot of badger and kit fox activity, and it can be challenging to tell the difference between all the types of desert holes. Tortoise burrows are shaped like a well-rounded half-moon with a flat bottom, and the sides are angled directly from the floor. The mound is well-rounded and clean. Occasionally tortoises will burrow in existing holes or in a washbank burrow. Keeping an eye out for tortoise scat in the mouths of these burrows is often the only way to tell if it’s being used by a tortoise. When we encounter a burrow, this gets measured, coordinates logged, and the burrow is assigned a grade from Class 1 (excellent/active) to Class 3 (fair/poor).
In order of frequency, the types of signs typically found on these excursions are as follows: scat, burrows, carcasses, live tortoises, drinking depressions, tracks, and eggs or eggshell fragments. In fact, it’s been determined that for every 44 pieces of scat found, one live tortoise is seen.
Scat is an excellent indicator of tortoise presence, and it can tell us a lot about what they are eating and how recently they’ve been through an area. Tortoise scat is distinguishable from that of other creatures because the material is generally large and not well-chewed, and the plant matter is generally oriented linearly. It also reportedly smells like chewing tobacco. We found some great scat specimens on this trip, including one that had an entire beetle in it!
In addition to scat and the eggshell fragment, we did find a few vacant shells and shell fragments. Though sad to see, the carcasses can offer further insight into health of the tortoise populations. The two main objectives when encountering a tortoise carcass is to estimate the time since death (evident by the luster of the shell), and to determine the cause of death (which can sometimes be determined by assessing the carcass and its surroundings).
In the event a live tortoise is found, our biological consultants would note the size, sex, and health status of the tortoise, including any shell or bone abnormalities and injuries.
Since 2017 the team has located ten live tortoises in the Chuckwalla Bench.
4:30 pm — After our survey we head back to camp. Following dinner and clean-up, we sit around sharing stories while we all struggle to stay awake. By 7:30 pm we retire to our tents, and I fall asleep to the tune of Ed strumming his guitar and singing “Coat of Many Colors” with a voice like honey on a spoon.
Did you know? As well as managing conservation easements, MDLT has acquired over 11,000 acres of critical desert tortoise habitat across the California desert.
Want to support desert tortoises in your own backyard? Learn their preferred plants here.
Invasive plants can harm desert tortoises and other native wildlife. Learn how to help manage invasive plants in the Mojave.