Monday, July 15, 2013
Styrotorts in the Desert
In my second week with the NCC, our crew drew a rare local gig helping Terry and Kirsten with their desert tortoise monitoring project with the Great Basin Institute. This meant that we would be going home each night, or at least staying somewhere in or near Vegas, instead of camping in the field as is the norm. Our task was to aid in the setup of a course designed to test the skills of the hires for the GBI who would be spending time walking about the desert in search of tortoises in the coming months. These folks would be roaming sections of the Mojave using the Line Distance Sampling (LDS) method of determining population density, location, and movements.
The majority of our time was spent walking around in the desert near the San Diego Zoo's Desert Tortoise Conservation Center (DTCC) just outside of the Vegas sprawl, armed with measuring tapes and compasses, locating fake weighted styrofoam tortoises ("styrotorts"). We were to make sure they were numbered correctly, weren't too heavily damaged, and had not moved from the year prior, be it from a flash flood, a deceived and vicious raven, a freewheeling off-roader, or whatever else. In the end five were unable to be located, many required paint touch-ups, and plenty were found slightly out-of-place.
As we systematically measured straight line distances and shot compass bearings across two ~65 acre rectangular sections of land, we also took occasional moments to teach each other and talk about the flora and fauna of the area. Between my generally knowledgeable fellow crew members and Kirsten, who was along with us for the entire week, I learned plenty about the Mojave desert, the impact of Las Vegas on the surrounding environment, tortoises, and some of the other plants and animals of the area.
The desert tortoise, Gopherus agassizii in the Mojave, is a very interesting creature. It naturally lives up to 50+ years, and potentially many more if in captivity. In order to conserve water and regulate temperature in such a harsh and dry environment, the tortoise spends much of its time hibernating or in an inactive state in its burrow, and can store up to 40% of its body weight in fluids in its bladder, which can be reabsorbed when needed. Since rain is uncommon, the tortoise gets much of its water from its plant-based diet, and if caused to evacuate its bladder due to stress, may not be able to recover enough water to survive in the long run. Tortoises are most active when temperatures are between 79 and 93 degrees or just after rain, and so we didn't see any live ones in the desert ourselves. After a female lays a clutch of eggs, the sexes of the hatchlings are determined by the temperature of incubation: lower temperatures generally result in all male clutches.
In the Mojave, the desert tortoise was listed as a threatened species in 1989, primarily due to increased predation and habitat loss, both of which are aided by human development. It is therefore illegal to kill, remove, or even touch a desert tortoise. Kept as pets for a long time, those already in captivity can remain so but wild tortoises may not be captured. Every year in Clark County, dozens of tortoise owners decide they no longer want their pets, and some of those wind up in the hands of the staff of the DTCC via the desert tortoise hotline. At the DTCC they treat those requiring more attention and generally prepare the tortoises for translocation back into the wild. When we had finished checking and resetting the styrotort LDS training course, we got a chance to chat with one of the DTCC researchers and see some of the tortoises being kept in more controlled conditions for treatment / monitoring. And so I leave you with a photo of the tiny tortoises in a bin at the DTCC: