Habitat degradation, vandalism, and predation are contributing to desert tortoises' low numbers in Mojave National Preserve.
By Jenell Talley
Catching a glimpse of the Mojave desert tortoise is like finding a needle in a haystack. People have always seemed intrigued by the charismatic creatures, collecting and trading them for years. Hundreds of thousands are suspected to be in captivity. Unfortunately for the tortoises, however, their popularity has contributed to waning numbers. |
Mojave desert tortoises eat a variety of plants, including cactus pads. | |
A multitude of activities, including commercial, residential, and agricultural development, livestock grazing, and off-highway vehicle use has reduced the population significantly. The species has all but vanished in western parts of the Mojave Desert, despite their ability to subsist in scorching desert terrain.
Today, upper respiratory tract disease and predation on hatchlings by ravens are two of the creatures' biggest threats. Badgers, kit foxes, and coyotes also prey on the tortoises' eggs. Limited soil suitable for digging burrows, where the animals spend roughly 95 percent of their lives, and a shell disease characterized by lesions also affect their distribution. Deterioration and loss of habitat remain threats, as do vandalism, mining, and the illegal collection of the species.
Desert tortoises are one of four North American species known collectively as gopher tortoises, characterized by their eight- to 15-inch brown shells. The Mojave population is the only desert tortoise species listed as threatened. These animals are the largest reptiles in the Mojave Desert.
The Mojave tortoises have columnar hind limbs, lending to the species' primal appearance. When walking, the butterball-shaped tortoises, that often live to be as old as 80, extend their elephant-like legs, lifting their shell off the ground. Their top shell, the carapace, is domed; the bottom, the plastron, is flat on females and inverted on males. They use the inner edge of their forefeet to walk, sometimes traveling up to seven miles per day. The tortoises have flattened, muscular forelegs and clawed toes that they use for digging underground burrows. They have no teeth, forcing them to use their sharp-edged jaws to bite.
The Gopherus agassizii is an herbivore that lives on sand or gravel desert between 1,000 and more than 4,000 feet in elevation. They are generally found in creosote bush habitat but are known to occupy a broad range of plant communities in the Mojave. Their eating habits vary by range, but herbs, annual forbs, grasses, shrubs, cactus pads, and fruit make up the bulk of their diet.
Tortoises are terrestrial creatures, seeking water only to drink or bathe. Adults can survive more than a year without any water.
Tortoises have long been fixtures in desert ecosystems, dating back some 280 million years. Early on, desert tortoises thrived. During the 1920s, there were 1,000 desert tortoises per square mile in the Mojave Desert. By 1990, the U.S. Fish and Wildlife Service listed the Mojave population as threatened.
The U.S. Fish and Wildlife Service has developed a recovery plan for the Mojave population. Its de-listing criteria include: creating management actions, protecting and efficiently managing the species' current habitat, and developing a scientifically credible monitoring plan that will effectively monitor trends in the species' population density.
Despite all the threats the tortoise faces, Kitti Jensen, the wildlife biologist at Mojave National Preserve, holds out hope. She says the Mojave population can be removed from the federal list if the recovery plan is followed.
Jensen believes that a better understanding of the natural world could lead to people caring more about endangered and threatened species, such as the Mojave desert tortoise.
"When people understand the natural world, then they develop a passion about it," she says, adding, "Plus, [the tortoises] are so darn cute."
| JENELL TALLEY is publications coordinator. | |
