Desert tortoise population, habitat use and genetic surveys being conducted
KINGMAN "We've got one a big one"!
Steve Goodman, nongame biologist for the Kingman branch of the Arizona Game and Fish Department, peered inside the dark recesses of a half-quarter-shaped burrow nestled in a rocky desert wash and grinned triumphantly. I made my way down the wash as Goodman placed a large backpack beside the tunnel, took some items out and began to record data.
We had been searching for the elusive creature all morning long, and here it finally was, found on the last stop of the day. Our quarry: the desert tortoise.
Goodman had taken me out to the west slopes of the Black Mountains this sunny spring day to explain the AZGFD's work with these elusive reptiles and, hopefully, to show me one. We tromped through rocky hillsides and sandy arroyos, finding numerous burrows, droppings and even old pieces of tortoise shell, but had not seen the living animal.
Our last stop was in an area not yet surveyed for tortoises, but it was one that Goodman had a good feeling about. His hunch proved correct as we found burrow after burrow, and finally the living animal tucked several meters inside the earth's surface. All I could see was one hind foot and part of the tortoise's shell. I tried to take a photo, but the angle and lighting just wouldn't work for me. It struck me again how surprisingly elusive this seemingly slow and disadvantaged creature can be. But they say if it ain't broke don't fix it, and the tortoise has successfully thrived in the Arizona desert for a very long time.
The desert tortoise is an animal whose body shape has remained virtually unchanged for millions of years. Fossil evidence of the tortoise family goes back 200 million years. The tortoise is a dry-land turtle that doesn't swim. Instead, its strong, elephantine front legs possess long claws adept at digging in the rough ground of the desert. It prefers rocky hillsides, where it can dig for shelter and eat various cacti, fruit, flowers, grasses and shrubs. Tortoises cannot create their own body heat and may bask in the sun or seek the coolness of shade, depending on their needs. Tortoises may grow to weigh eleven pounds and reach a length of nine to thirteen inches. They may live up to eighty years or longer.
These ancient animals have garnered a lot of recent scientific interest. The Mojave tortoise, classified as occurring north and west of the Colorado River, is listed as a threatened species. Sonoran tortoises, found south and east of the Colorado River, are a protected species but not classified as threatened yet.
However, many new developments are being planned in tortoise habitat. The area of the Black Mountain ecosystem found south of Highway 68 and north of Interstate 40 has been designated by the Arizona Interagency Desert Tortoise Team as a Key Habitat Area under their Sonoran Desert Tortoise Conservation Strategy. Biologists from the AZGFD and the Bureau of Land Management (which oversees a good-sized portion of this area) conducted a threat analysis in 2005 and determined that the threat to tortoise population viability for the next 10-20 years is high for this Key Habitat Area.
If tortoise habitat use can be more thoroughly understood, people will be better able to make management decisions that allow both people and tortoises to make their homes here for years to come.
With that goal in mind, AZGFD and other agencies are conducting tortoise population, habitat use and genetic surveys in northwestern Arizona. In the Black Mountains west of Kingman, there is a lot of terrain which would seem to be tortoise-friendly.
However, the AZGFD is finding that tortoise distribution is actually rather patchy in many areas that might have been thought of as tortoise habitat. The department has conducted over 240 miles of transect surveys in the Black Mountains since February 2004. According to the surveys, the most important tortoise habitat of these mountains seems to be the mid- to lower-slope bajadas, which are broad slopes of debris spread at the bottom of mountains by descending streams and washes.
In addition, soil and geologic-based surveys are being conducted to paint a better picture of where the tortoises actually are. There are dozens of different soil types in the Black Mountains, and tortoises may prefer certain soil types from others. The right kind of soil allows a tortoise to safely bury its eggs and to dig burrows, which are vital in allowing the reptile to escape the heat of the summer sun. Non-preferred soils may be too hard to dig in or may be so soft that burrows collapse.
The importance of the burrow to a tortoise cannot be overstated. Tortoises dig deep holes that stay noticeably cooler and more humid than the scorching surface of the summer-time desert landscape. Tortoises can hole up for long periods, even months at a time, when necessary. This allows them to retain the moisture they have and survive extended periods of drought.
Tortoise burrows are also important to other animals in the ecosystem. In fact, research suggests that tortoise burrows may be a vitally important part of the desert landscape, helping upwards of 100 other species in their struggle to survive the hot desert climate. Burrowing owls, kit foxes and chuckwallas are just a few of the species that benefit from the tortoises' work.
Research in Barstow, Calif., suggests that the tortoise is a "keystone species" in an old-growth environment, meaning that the animal is a species that plays a dominant role in a particular ecosystem and is one that many other animals depend on. If tortoises disappeared, their loss would impact many other wildlife species.
Their loss would also impact the humans who love the desert and the amazing life forms that are able to survive within its harsh beauty. As Steve Goodman related, "Tortoises have been here for millions of years. They are the quintessential desert species when you think about the desert, you think desert tortoises." He also spoke of the obligation we have to future generations so that they can know the tortoise and the ecosystem it is part of.
People can have a great impact on tortoise numbers. Habitat destruction is the number one problem for wildlife today, and tortoises are not immune. When new houses are built, tortoises and their burrows may be bulldozed over or the reptiles may be run over on newly created roads. Studies show that tortoise numbers tend to drop about a mile's radius from houses or roads, often due to increased human activity.
Users of off-highway vehicles/ATVs are encouraged to stay on legal roads and trails, helping to prevent the accidental crushing of tortoises. Wandering pets may also kill the reptiles, and humans may pick up tortoises they find and keep them.
This last issue is important and one of the most easily preventable problems facing the tortoise today. When handled, tortoises often empty their bladders, losing moisture which can make the difference between life and death during times of drought. People are encouraged to never pick up a wild tortoise, but enjoy it from a distance.
On rare occasions there is an urgent need to move a tortoise immediately, such as an animal crossing a busy road. In this situation, one is advised to pick the tortoise just a few inches from the ground, where its toenails are still almost touching the ground, and then "glide" the animal to safety in the direction it was heading. Wild tortoises belong in the wild and are needed there to help replenish the population. It takes tortoises about 12 to 20 years to reach sexual maturity, and few make it that long, so each animal that does is a true asset to the population's survival.
Once a tortoise is removed from the wild, it can never go back. Captive tortoises can catch diseases (such as upper respiratory tract disease) that can decimate wild populations if the infected animals are released back to the wild.
However, anyone who wants a tortoise as a pet and has the right facilities to care for it is in luck there are many captive tortoises available for adoption through the AZGFD, and if people meet the criteria they can provide a home to one of these amazing animals. Call 692-7700 for more information. With care and conscientiousness, people can ensure that this ancient reptile will continue to shape the desert landscape for many years to come.