Mojave Desert Tortoise

Desert Tortoise - Desert Survivor?

Ever wonder why there is such uproar when there is something that involves the Desert Tortoise (AKA gopher tortoise)? After all it’s just a turtle, you can buy them at the pet store, right? In this case, WRONG. There are significant differences between the two. Both reptiles are from the order of Testudines, but with different family classifications. The major difference between the two is that tortoises are land dwellers, whereas turtles live in or very near water at all times. The bodies of both tortoises and turtles are shielded by a shell, the upper part is called a carapace, the lower portion is called plastron. These two parts of the shell are attached by a bridge, meaning that the head and limbs of both the tortoises and turtles may be withdrawn from the shell; the whole body can never be detached from the shell.

Both tortoises and turtles lay eggs on the ground. The mothers will dig a burrow and lay two to twelve eggs. It takes from 90-120 days for the eggs to hatch. Once the hatchlings emerge from the shell, they dig their way to the surface. The annual death rate of adult tortoises is typically only a few percent, but it is much higher for the young. Only 2-5% of hatchlings are estimated to reach maturity. Estimates for the desert tortoise hatchlings to reach 1 year of age is 47-51%. And survival from 1-4 years of age is 71-81%. In a laboratory experiment, temperature influenced hatching rates and hatchling gender. Incubation Temperatures of 88 degrees or less resulted in all males. Temperatures above 91 degrees resulted in all females. No mortality rates were available for turtles.

Turtles have webbed feet with long claws that help them climb onto logs and rocks, and flat and streamlined shells that aid in swimming and diving. Tortoises are herbivores and turtles are omnivores.

Bright Source Energy’s (BSE) Ivanpah solar project was paying as many as 100 biologists to be on site at one time. The company warned that the tortoise mitigation was jeopardizing Ivanpah’s viability, costing the company as much as $40 million ($241,000 per tortoise). At Ivanpah today, 166 adult and juvenile tortoises have been collected and moved to a nine-acre holding facility. The objective is to release them back into the wild on the other side of the fence at the solar facility. BSE’s difficulties with the tortoise raise hackles among people who believe the government protections afforded is extreme. Even before solar power entered the picture, state and federal governments had spent nearly $200 million since the endangered species listing in 1990.

In an effort to save the desert tortoise, conservation groups have settled on a simple fix: just move them. Over the last decade, hundreds of tortoises have been relocated and there are plans to move thousands more. Is relocation really a good solution? Biologists and tortoise conservation groups say it’s a $10 term for moving animals from where they are to where you want them to be, so you can build over their habitat. This is something that the Fish and Wildlife service has been doing for a long time to other species. They have been airlifting big horn sheep from one part of the Sierras to another. The problem with doing it to the tortoise is they have a finely tuned homing instinct. They seem to know where they were taken from and try to get back.

You may remember as recently as 2008 as part of the Fort Irwin expansion when they moved hundreds of animals. One of the scientists who studied 150 tortoises; five years later half were dead. During a large expansion of Las Vegas more than 9,000 were moved — no one kept track of them. When the tortoise coordinator officer was interviewed about not tracking them, the answer was, “well, we haven’t really pulled the data yet,” but if you go out there, you will find a lot of dead tortoises. The number of live tortoises they were able to find only numbered 535. That is nearly a 95% mortally rate!

Now we have the 29 Palms Marine Base wanting to translocate (new word for relocation) nearly 1,500 tortoises from the 88,000 acres that was taken from OHV in Johnson Valley. Not only did the Marines throw out the OHV users, now they’re throwing out the only real owners of the land. William Boarman, a wildlife scientist and expert on the desert tortoise, said, “relocation is not a conservation strategy or a means of helping tortoise populations grow. It’s simply a way to move them out of the way.” But Walter Christiansen, head of environmental planning at the base, is optimistic. “We’ve learned a lot from past mistakes of others” he said. “We wouldn’t be doing this if we felt the desert tortoise wasn’t viable in the Mojave.”

Val and I spent about 45 minutes speaking with Brian Henen, a biologist and head of the Marine Corps' translocation effort. He said the project’s significant budget and commitment to monitor the health of the tortoises for 30 years demonstrates “how much we care about the species.” Speaking with these guys is like talking to a used car salesman. They are always trying to convince you that they have the right answer. They say they will move the tortoises in the cooler time of the year. So did the Fort Irwin translocation. There is no peer review of this plan that I could find, but there is plenty of disagreement among other biologists.

“I wish the Fish and Wildlife would get some backbone and say they can’t permit another tortoise translocation by the military,” said Glenn Stewart, a biologist and member of the board of directors of the Desert Tortoise Council conservation group. “The situation makes us feel like we’ll have to write off the California population.”

Tortoise relocation is a tough issue. Animals that have been moved nearly always try to find their way back home guided by some uncanny sense of direction like that of the homing pigeon. Tortoises know when they’re not home! At home, they know where the food is, they know where the water is; tortoises live a long time and have good memories.

California requires developers to provide two acres of suitable tortoise habitat for every one acre that is to be developed. But the scale of the solar development coming into the desert of the Mojave is so vast that it renders the formula unworkable. Not enough alternative land exists. Instead, solar developers may now pay to close off OHV routes, rehabilitate degraded habitat on federal land, fund public education programs and erect miles of special fencing to keep tortoises off highways and out of solar sites.

Desert Tortoises (teststudines; teststudinidae; Gopherus agassizii group) have an extensive distribution throughout the Mojave, Colorado, and Sonoran desert regions. It’s not surprising that they exhibit a tremendous amount of ecological, behavioral, morphological, and genetic variation. The Desert Tortoise was a single species for almost 150 years. Until recently it was decided that there were actually two species of the desert tortoise. They have been classified based on behavioral deviations, DNA and geographical differences; between those that live on the east and west sides of the Colorado River.

The two species are Agassizi’s desert tortoise (Mojave), and Morafka’s (Sonoran) desert tortoise. But there is also the Bolson Tortoise (Gopherus Flavomarginatus), also known as the Mexican giant tortoise, or the yellow-margined tortoise. It is a species of tortoise from North America. It is the largest of the four North American tortoise species, having a carapace (upper shell) of 19 inches compared to the Mojave and Sonoran, which is around 15 inches for an adult male. It lives in a region of Chihuahuan Desert known as the Bolson de Mapimi, located in north central Mexico. This tortoise was just discovered in 1959! As the story goes, a group of biologists working in the Bolson de Mapimi were at a ranch and saw chickens eating out of a large tortoise shell, when they inquired, they were told by the locals it was la tortuga grande del desierto, (big turtle of the desert). As of 1983 fewer than 10,000 giants remain in the wild.

In February of this year yet another species of desert has been discovered. In a University of Arizona press release in February of 2016, the turtle called Goode’s Thornscrub Tortoise was discovered in Sinaloa Mexico, in thorn scrub and tropical deciduous forests. It is only found in these areas, according to UA geneticist Taylor Edwards and because of this, it has the smallest range of all other three known desert tortoises.

Tortoises are over 200 million years old and are a cornerstone of the desert ecology. Tortoises are extremely important to a lot of animals. Burrowing owls, reptiles; various types of mice in the desert as well as the kangaroo rat (Endangered Species) rely on the burrows that the tortoises dig. They have burrows that they hibernate in during the winter and one tortoise can have as many as twenty different borrows that can be shared with other tortoises. Next time you are in the desert take some time and walk around. When you see a bush, look at the root base and a lot of times you will see a burrow entrance. Just because you don’t see the tortoise that doesn’t mean they aren’t around. The desert tortoises were not always so scarce. They thrived in a harsh environment with the few tools that nature had provided.

To ward off predators, they spritz pungent bladder contents around their burrows, where they spend as much as 95% of their lives. When tortoises hear thunder, they come topside and lower the side of their shell and like a little bulldozer, they dig out water catchments. They have many such catchments and remember where they all are located. The tortoise can increase their body mass by 30-40% by guzzling water in this fashion; this can sustain them for up to 2 years or more without another drop.

The tortoises were once so abundant that people who visited the desert used to bring the small one’s home as souvenirs, and the animals lived long lives in suburban back yards.

Once the tortoise was listed as endangered in 1990 a reverse diaspora occurred. Panicked tortoise owner’s streaked back to the desert and released the now protected tortoise. But the story gets worse. The former captives brought with them a disease; an upper respiratory disease (aka pet store disease) that spread and killed tortoises across the Mojave.

All species of Gopherus shared the following morphological characteristics with other members of the family Testudinidae; 11 marginal scutes (boney external plates on the shell) on both left and right edges of the carapace, 5 toenails on each forelimb and 4 toenails on each elephantine hind limb. Within the desert tortoises and like the Mojave and Sonoran the Sinaloan lineage tortoise was sexually dimorphic with the mature males having a slightly longer tail, enlarged gular horn, a concave plastron, tucked and prominent chin glands. However, several characteristics generally distinguished the Sinaloan lineage from other desert tortoises. The Sinaloan tortoise has a very flat carapace that is significantly flatter than the higher domed carapaces of the Mojave and the Sonoran.

Because the desert tortoise live in a dry arid region it is not easy for them to get a constant supply of water and by not having a constant source of moisture they live a dormant life of hibernation between late October/November and February/March. During these periods, they mostly live inside their burrows in order to escape loss of body water, and for protection against the summer heat. Their heart rate, respiration, and all other bodily functions slow down.

Desert tortoises are herbivores. As a rule, they feed on the many varieties of perennial wild flowers and annual grasses, fresh buds and pads of some species of cactus.

During mating season, the male will grow two large white chin glands, around the chin to indicate the onset of the season. Tortoises mate mostly between spring and fall. The stronger the male, the higher his chances are to win a female partner for mating. However, just like humans, the female makes the decision with whom she will mate.

 Some Tortoise Facts

  • Length: a mature male will be around 14 inches, hatchlings 2 to 2-1/2 inches in length.
  • Carapace (upper shell): Mojave and Sonoran have a distinct high-doomed, roundish carapace. The Sinaloan tortoise has a very flat carapace. The length of the carapace is from 9 to 15 inches for mature males.
  • Plastron (lower shell): females have a flat plastron that is slightly expanded in the rear.
  • Height: tortoises stand 4 to 6 inches from the ground.
  • Head: relatively narrow. Upper jaw ridges meet at an angular point.
  • Eyes: eye rings are light while the iris is yellow to greenish yellow.
  • Beak: protruding out like most tortoises, the beak is used mostly to tear food.
  • Horn: both genders have a gular horn, which is an anterior extension of lower shell. Tortoises use these horns for defensive purposes.
  • Mating: female desert tortoises may copulate with several males and store the sperm for several years until she is ready to lay eggs.
  • Longevity: Sonoran Desert tortoises live longer than those in the Mojave.
  • Swimming: tortoises are poorly adapted to swimming, they have trouble keeping their nostrils high enough above the surface of the water to breathe.
  • Tail: tortoises have short tails.
  • Lifespan: tortoises live for a minimum of 35 years; however, some have been recorded to live 50-100 years. The female has a shorter lifespan.

Tortoises can live in areas where the ground temperatures reach 140 degrees, because of their ability to dig burrows to escape the heat.

After about a week’s worth of research for this article, I have gained a new respect for the plight of the tortoises. I do believe we must do what we can to protect the tortoise. It is certain that the government entities will always bow to the power or the almighty dollar. We, as users of the desert, can do our part by not traveling cross country, unless it’s an established route. Remember, tortoises build their burrow entrances at the base of bushes. Give them a wide area so you do not collapse a burrow. With the numbers of the tortoise dwindling every day, it is up to us to make sure that we don’t add to the demise of the Desert tortoise.

In an article by David Danelski, he writes it’s going to be a stressful time for about 1,500 desert tortoises, a species listed as threatened with extinction. They will be scooped up from their long-established home ranges in the Mojave Desert and flown by helicopter miles away. Most are expected to survive the move. Such was the conclusion of a 250-page environmental analysis commissioned by the US Marine Corps. The tortoises would “experience stress during the move and the time it takes them to establish a new home range,” the report said. According to the report, the risk of death “is small, unquantifiable, and not statistically significant.” The total wild population of the Mojave and Sonoran desert tortoise stands at about 100,000 tortoises — even one death is unacceptable. Tortoises are very slow growing and when they contract the respiratory virus it may take several years for them to die. Some biologists say that the death rate of tortoises is higher than the birth rate. This is mostly because of encroachment and predation and OHV users, there’s not much we can do about the first two, but we can have an impact on the latter by staying on trails.

The Center for Biological Diversity (CBD) has filed legal notice, saying the environmental reviews were inadequate. The CBD specifically requested more analysis on how the move affected tortoises and other wildlife living in the release area.

Tags: desert tortoise

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