Environmental Management at Edwards Air Force Base, Calif., is partnering with San Diego Zoo Global and the United States Geological Survey in an effort to increase the desert tortoise population through head-starting and translocation research.
The desert tortoise grows slowly and lives for a long period of time. According to San Diego Zoo Global, the animal has not changed much in the last 200 million years. The desert tortoise is listed on the Federal Endangered Species List as threatened as of 1990. Even with conservation, desert tortoise numbers continue to decline quickly according to Wesley King, 412th Civil Engineer Group, Environmental Management Division biological scientist.
“If the population continues to decline the desert tortoise will change from being listed as threatened to endangered, which means it will be in serious danger of becoming extinct throughout all or a portion of its range.” said King.
Edwards AFB is hosting the desert tortoise head-start study and providing use of the base’s head-start pens to allow San Diego Zoo Global and United States Geological Survey to study the tortoises.
Through a grant from the California Energy Commission and matching funds from San Diego Zoo Global and the United States Geological Survey, nearly $1 million of desert tortoise head-starting and translocation research will be conducted at two sites in the Mojave Desert, one of which is here at Edwards AFB.
“Head-starting increases the likelihood of survival of newly hatched tortoises by providing a controlled environment protected from predators during their most vulnerable stage of development,” King said. When the desert tortoise has grown to a size where survival is more probable, it is then released into the natural desert environment.”
A previous head-start program was initiated in 2002 at Edwards AFB and resulted in the construction of the desert tortoise head-start pens. The pens are designed to replicate the natural environment of the western Mojave Desert. Following construction of the pens, there have been modifications to include the addition of a watering system, which occasionally releases water to enhance the growth of natural vegetation. From 2003 until 2010, female desert tortoises were brought into the pens where they would lay their eggs. Then juvenile tortoises were released into the wild and are still currently being monitored.
New, wild female desert tortoises are located and a determination will be made if the tortoises are healthy enough to be used in the study. According to King, a biologist conducts a health assessment when a female desert tortoise is located in the wild to see if the tortoise is healthy enough to use as a source for eggs. The health assessment also looks for symptoms of diseases by examining nasal and ocular discharge, lethargy, low body condition index and conjunctivitis to name a few. The biologist collects blood samples to be tested in a laboratory to make a final health determination.
When the desert tortoises are released, they are released in areas with relatively low predator activity. Biologists assist the release process by knowing locations where predator densities are high. Predators of the desert tortoise are vast and include; “common ravens, coyotes, kit foxes, feral dogs, red–tailed hawks, golden eagles, loggerhead shrikes, American kestrels, burrowing owls, greater roadrunners, mountain lions, ground squirrels and even people.”
Before the desert tortoises are released in 2020, each tortoise will have a transmitter attached to the top-portion of its shell. The receiver can track each tortoise on a monthly basis.
“The receiver is able to be adjusted and selectively pick up different frequencies and guide the receiver toward the transmitter, which enables the biologist to determine each animal’s location fairly accurately,” said King.
The transmitter signals can be used to determine their location and if the tortoise is able to be found, the biologist will attempt to determine if they are alive or not. The mortality status will be one of the most important pieces of information collected for the study, according to King.
Continued research after two to three years will depend on what type of funding San Diego Zoo Global can obtain. This will determine what direction the study will go.
It is difficult to maintain the desert tortoise’s disappearing habitat when there is an ever growing need for the development of land.
“On Edwards AFB we take desert tortoise conservation very seriously and the Environmental Management Division takes a proactive stance on protecting this delicate species,” said King. “Being a military installation, we are able to provide additional protections for the tortoise that would not be possible on other publicly accessible lands, and lands where large-scale development occurs on a regular basis. This is an additional benefit of hosting this program on our base.”