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The Heat Is On: Desert Tortoises And Survival

31 minutes

(male narrator) Hello, newborn desert tortoise. Welcome to your world. Look around. Break out of your shell and explore what lies ahead. Stretch your legs. Feel the desert soil. One thing for sure though, it won't be easy.

This is a male? Yeah. Oh yeah, look at that tail.

(female) It appears that the desert tortoise is in trouble.

(male) At eight or nine study sites, we saw declines from 30% to 50%.

(male #2) The tortoise started having sever population declines in about 1989.

(female) Very few of the small tortoises survive. There's about a 95% mortality rate within the first five years.

(male) We're seeing declining populations due to a variety of factors-- not just disease, predation, or habitat loss, but a mix of all those things are really causing some declines that I hope we can reverse.

(narrator) Desert tortoises have lived across the Southwest landscape for thousands of years. Their adaptation to its extreme harsh environment is amazing, surviving ground temperatures greater than 130 degrees Fahrenheit and able to live a year, or even two, without water. But now the desert tortoise is in danger of extinction. In the 1920s there were hundreds of desert tortoises per square mile in parts of the Mojave Desert. Now there may be fewer than a dozen per square mile. Tortoise extinction would have a ripple effect across the desert. As tortoise numbers drop, so too do the numbers of underground burrows that they dig. A wide host of animals depend upon these burrows for shelter from extreme summer heat and the cold of winter. Even in a protected critical habitat area like the Red Cliffs Desert Reserve in southern Utah, the tortoise population dropped nearly 50% since 2000. But perhaps science can yet turn the tide. Science can give us a lot of information on how best to manage populations and areas in which the tortoises live. I work with the Desert Tortoise Recovery Office. Our job is to facilitate recovery efforts for the species. There's four states, three Fish and Wildlife Service regions, countless agencies, and stakeholders and interest groups and researchers.

(narrator) Much of the research guiding the recovery effort is being carried out by ecologists and biologists with the Department of the Interior, U.S. Geological Survey.

(male #3) USGS researchers are conducting a really great variety of research, including tortoise physiology, general ecology, their responses to fires, disease and health, hibernation, reproduction, all aspects of their ecology.

(Averill-Murray) What works, what doesn't work.

(Jones) The more we can learn the better chance we have of bringing it back.

(narrator) Because the Mojave Desert tortoise is listed under the Endangered Species Act, there is a federal mandate to restore the populations. The tortoise is among the top recipients of federal dollars, because their decline has been quite sudden and wide ranging. And because they are so long-lived, it takes years to know which recovery efforts are working or not.

The Mojave Desert covers some 25,000 square miles. It is a part of Utah, Arizona, Nevada, and California. Over 30 years ago, USGS researcher Kristin Berry set up 27 study plots in the Mojave and adjoining Colorado deserts. These plots were designed to help understand how tortoise populations and their habitats might be changing over time.

(Berry) The long-term study plots provide a substantial amount of data on the status and trends in tortoise populations. They're places one can return to year after year, decade after decade, and find out how the tortoise populations are doing. I selected, for long-term study, fifteen of the plots that had an adequate sample size of at least 20 to 30 tortoises per square mile.

(narrator) These plots have all experienced declines in tortoise numbers and have helped identify some of the causes behind that decline. In this particular plot near Needles, California, the scientists are counting the numbers of the invasive plant Saharan Mustard. It is one of several invading plant species causing widespread change to Southwest deserts.

(Berry) There are 6,000 in this group on the same transect where there was a handful in 1999. The proportion of plants that we have now, ten years later, is just enormous. There's been major change.

(narrator) Exact impacts of this invasion are being assessed. The invaders take up precious water and nutrients. If the trend continues, there's likely to be a profound effect on native creatures such as the desert tortoise. Invasive plants pose other dramatic threats as well.

(Averill-Murray) One of the threats facing desert tortoises today is increased wildfires because of the invasion of exotic grasses and things which perpetuate a fire cycle that is not historically present in the Mojave Desert.

(narrator) The dry stems of spreading invasive grasses fuel devastating backcountry fires. Tens of thousands of acres of critical tortoise habitat have burned in one year. Native plant foods disappear. Shrub and shade covers are eliminated. Some tortoises have been burned to death.

(Averill-Murray) It appears this will be a recurring risk for a long time, at least until we learn how to manage invasive grasses.

(narrator) The Desert Tortoise Conservation Center was originally established as a way station for tortoises displaced by Las Vegas development. Today with the expertise and management by the San Diego Zoo and the U.S. Fish and Wildlife Service, it will fill a key role by providing a base for applied research, training, and community support. One of the USGS studies underway at the center involves a promising Head Starting program. Head Starting is taking place at several locations across the Mojave. It's a technique where captive tortoises lay eggs in pens, with the young being raised and later released, so that researchers can better learn about their survival. Since females lay the eggs deep in burrows, how do scientists know when the eggs are laid so they can get the eggs to incubate them? One-four-seven-two-seven. We X-ray the female tortoises every two weeks. Put the tortoise on the plate. I'm gonna shoot the X-ray now. Okay, stay back--done. Okay. This is one of the X-ray images we shot five minutes ago. This is tortoise 14-9-9-8. You can see five visible shelled eggs within the X-ray.

(Medica) If they lay eggs based on the weight change, we know at least six eggs that we X-rayed last week have been deposited somewhere inside the enclosures. We will go and find the nest and collect the eggs and put them in incubators to hatch hatchlings.

(female) They found an egg! Got one? Alright!

(Drake) Once the egg's laid in the ground, the incubation temperature will determine the sex of the hatchling. Warmer temperatures produce females. Cooler temperatures produce males. Once the eggs hatch in the incubators, we're gonna remove them from the incubator, put them in an outdoor enclosure, allowing them to get natural sunlight and the natural vegetation they normally would eat. Then monitor these animals and try to ensure survival as best we can.

(narrator) For desert tortoises to be removed from the Endangered Species List, populations must increase or remain stable for 25 years. Hey, baby tortoise, you're beginning an amazing life. The desert tortoise is the largest reptile in the Mojave Desert. Their lifespan is a bit like humans. Young are soft-shelled and vulnerable. Sexual maturity arrives around age 15. Males and females court. The female digs a nest for the four to eight eggs, each about the size of a Ping-Pong ball. The shell, called a carapace, has two layers-- bone underneath

and on top scutes made of keratin, like fingernails. Desert tortoises spend 90% of their time in underground burrows, which can be shallow or as long as 30 feet. There they hibernate in winter and stay cool in summer, when the burrow temperature may be 40 degrees cooler than the searing heat above. Desert tortoises can live to be over 50 years old. We're tapping him out with the hopes that when he hears noise, he's gonna charge from the burrow. Right on cue.


You ready?

(narrator) While deaths from upper respiratory tract disease triggered the endangered species listing, additional threats are multiplying. Ravens have become an increasingly deadly predator of young tortoises.


(male) The easiest place to find raven nests is underneath power towers. Yep, they're back for a visit. Sticks blown off the nest. Ohhh. Here's a tortoise that's been eaten by a raven. It's a characteristic that they'll peck a hole in the top to kill it.


In northern forests, such as Maine, ravens are still a wilderness bird. In the Mojave Desert, which has had urban sprawl and so many human modifications, ravens have increased up to 1000% in the last 50 years. The availability of food has just caused this huge population increase. They're social birds, and they congregate around landfills, sewage ponds, fast-food restaurants, cattle yards, horse properties, anywhere where there's easy food. But the ones that have learned to eat juvenile tortoises, they can decimate a generation of tortoises right around the nest. Those ravens are targeted. If they find evidence of tortoise predation under a raven nest, then the Bureau of Land Management calls the Wildlife Services Department of the USDA, and they come out and kill the raven. The power company comes out and knocks down the nest. They're just so adaptable. They teach the young that tortoise is good eatin', so the next generation becomes a tortoise predator too.


(narrator) Desert tortoise recovery is enormously complicated because there is so much that scientists need to learn. For instance, just with the exotic non-native plants, what happens to tortoises who eat them? Or if spraying herbicides is used to control the invasive plants and the tortoises eat them, what then? We're studying the nutritional ecology of tortoises in relation to the wildfires that happened in 2005. The pens are armored to help keep the predators from eating them. About 25 of them are progeny from adults that were removed from this property when a housing development started. So we X-rayed those adult females, collected and incubated the eggs, and raised them at the Desert Tortoise Conservation Center the last six months. Today we took our first blood sample. We'll take blood three times yearly from the animals in this project. We'll study a variety of parameters-- mostly parameters to help us understand their metabolic fitness that would relate to some of the various treatments and their diet. The nutrition study is asking primarily, do tortoises on a native diet perform better, grow better, survive better than tortoises on an exotic unnatural diet?

(narrator) Much about the life of the reclusive tortoise is a mystery that scientists are beginning to solve with 21st century technology. For example, a customized GPS logging system collects more data over the vast desert landscape than ever would be possible with field crews. We've been on the leading edge for a long time in trying to get technology to help do a difficult job. Putting a radio transmitter on a tortoise means we've gotta have people that are on a monthly or weekly basis monitoring tortoise activity to get data on habitat usage and the body temperatures they're achieving. A company helps us miniaturize GPS's and now we have GPS loggers as small as the radio transmitter we used ten years ago. Now it's a transmitter, GPS, and data logger in one package. We're happy about working with technology companies to get things you have in your cell phone working for us on tortoises to help understand how they're using habitat.

(narrator) The GPS logger can follow and monitor the tortoise all day every day and everywhere it moves.

(Nussear) If I want to know if tortoises are using burned habitat after a wildfire and I only get one picture of each tortoise daily, it takes longer to achieve information than getting detailed information daily about how much time that animal spends in or out of burned areas. We're getting this now with people watching tortoises, but in the future, we can get more information and put a better picture together of what they're doing. We've been watching tortoise populations for the desert tortoise for a little over 30 years. Almost 40 years in some areas. Everything indicates that there's been a steady decline in populations over that time. Until recently, that was kind of a mystery. We knew that it was lots of influences. Only recently have we had the ability to get on the ground and collect massive information across the entire Mojave Desert and put it into analyses to understand the pattern for the Mojave. We're pining down pieces of that story about why we're having these declines. Did you say number two is the one without the transmitter?

[radio chatter]

Over the last five years, we've been working with scientists, including biologists, ecologists, plant ecologists, people who do GIS remote sensing, hydrologists, geologists, and geographers too to put together a desert tortoise habitat model. So looking at different elevations and rock types, different vegetation associations, different precipitation and temperature regimes, and how those combine to influence what we know as the current desert tortoise distribution.

(narrator) Shades from yellow to orange then red show good to ideal tortoise habitat, while dark blue is not tortoise habitat.

(Nussear) Here in the Mojave Preserve we have areas of high tortoise concentration and predicted high suitable habitat. Also blue areas where we predict low suitable habitat.

(narrator) The model's ability to predict habitat type is proving to have wide applications across the Mojave and into the future. It's an invaluable tool for guiding the search for best locations to site new green energy projects. The model can project this into the future, helping to clarify possible impacts of climate change. Model components, such as rainfall totals and temperature, can be adjusted to show how habitats will shift as the climate changes. The model helps scientists understand the desert tortoise on a range-wide scale over millions of acres. It has the potential to make a huge difference in desert tortoise recovery, helping to ensure that critical habitats will be suitable into the future. There's no one thing killing off desert tortoises. A multitude of threats are interacting. Scientists must prioritize which are the most important and which problems can be solved. Hey, baby tortoise, the heat is on. You have all the struggles of life in the harsh desert and dwindling habitat and there are new threats on the horizon. In pre-Western history of people moving out here, this was a giant wilderness. It was a very hostile environment to humans. About 100 years ago, the West began to be opened up with new trails for immigrants. Those folks were eking out a living in the low desert areas. Then the highway system was built that opened up the area. Widespread availability of lots of electricity and air conditioning made it a less hostile place. We've gone from an area of little islands of human habitat eighty and sixty years ago, to what is now becoming an area dominated by human influence with little tiny islands of open natural habitat left. That's where we still find tortoises is in these islands that are left.

(narrator) Not only has development encroached into the desert, scientists have recently found a pattern that shows human impacts extending beyond where people are living. There's a shadow that's much larger than the actual footprint of buildings and roadways. It's created by predators, such as coyotes and ravens that are subsidized by human food and waste. Living outside the edge of these areas, others have their eye on the desert too. There's a lot of sunshine in the Mojave Desert. And there's a lot of open land that energy developers and people really interested in reducing fossil fuels look at and say, "Look at all that sun. We can put solar fields there." Well, that's where the desert tortoise lives and other sensitive species.

(LePre) I think it's important that you put these solar projects and the windmill projects at the edge of the desert-- the western edge or maybe the eastern edge or near major cities. But not in the middle. Then you're bringing an industrial park into the middle of tortoise habitat. So siting of energy projects is crucial. The first priority being to put them on lands already disturbed or where there is no tortoise habitat. The second being not to fragment large areas that are a uniform block of habitat.

(Averill-Murray) The challenge is finding the right balance to be able to achieve our alternative energy goals while not sacrificing the native landscape and our natural heritage at the same time.

[thunder cracking]

(narrator) One definition of desert is a landscape that gets less than ten inches of rainfall a year.

(Esque) A good year, maybe one in ten, the desert has a really good winter rainfall. In those years, it's just unbelievably spectacular.

(narrator) In the Mojave and Sonoran Deserts there live nearly 150 species of mammals, including mountain lions, ground squirrels, and desert bighorn sheep... along with 70 species of amphibians and reptiles and more than 300 species of flowering trees, shrubs, and wildflowers.

(LePre) The desert grows on you. It's fabulous in the spring. The spring bloom is the most dramatic change of season of any other kind of ecosystems in the U.S. probably. From brown to green to color all within a month.

(Esque) This year was an above average year. We sponsored field trips for many international visitors. Everywhere we found 15 or 20 species of wildflowers growing. It was a super abundance a month ago when things were fresher. Every time you go around a corner you wonder what's gonna be around it. There might be a Gila monster, a tortoise, or a snake. You never know what you're gonna find. It's fun to be here when it's reasonable in the spring.

(narrator) These desert-adapted plants and animals may hold some keys to human survival in a rapidly warming world. The unique genetic makeup of desert plants and animals is a sort of resource for the future, potentially crucial for developing new crops, livestock, and medicines as our climate warms. In the Mojave, over the next 50 to 100 years, temperatures are expected to rise between five ten degrees Fahrenheit. Rainfall is expected to decrease. Will temperatures in some places be greater than tortoises or their eggs can tolerate? What will happen to the plants making up their diet? How will tortoise habitat change? Science is the starting point for addressing these questions. There is already a foundation of scientific knowledge to build on. Tools, such as the habitat model, can help forecast some effects of climate change, while guiding management of habitat and species. Mounting threats to the tortoise now include invasive plants, disease, wildfires, roads, ravens, coyotes, off-road vehicles, other predators, and now climate change. The question remains, can the tortoise population stabilize and thrive? People know and care about the tortoise. I think that one thing may be the biggest thing that helps turn it around. We've gotta have people that want to help and people that care. That's coming around, and it's positive.

(Esque) We're dealing with 60 million years of evolution. Desert tortoises have been around a long time. People revere them for that reason. The general public wants to know there are tortoises on the landscape that are not there for their viewing, but they're existing in a natural habitat on their own.

(narrator) Humans, collectively, have had a big negative impact on desert tortoise habitat. But people, individually, can make a big positive difference too.

(LaPre) If you see a wild tortoise, look at it, take its picture, see what it's doing. It's something to appreciate, but not to mess with. It is good to take a good look so you really can understand the essence of tortoise, half of which is pulling its head in its shell and staying like that for an hour.

(narrator) Before dawn, the scientists' work begins.

Science is critical to desert tortoise recovery because there's a lot of uncertainties in how all the numerous threats that face the tortoise interact and affect tortoise populations. Without science, we wouldn't be able to sort any of that out. And anything that we did on the ground would just be a crapshoot. I find the tortoise to be very fascinating because it seems like such a meek species, but it's been able to survive all these years out in the desert. More and more as we're facing bigger threats, we need to use whatever science we can to understand how these animals are responding.

(Berry) The tortoise tells us so much about the health of the desert. It's a very long-lived animal. It's a sentinel of the well-being of our environment. For that reason alone, I think we should be very concerned about it's well-being and that it thrives.

(narrator) Building on our knowledge of the tortoise, its habitat and threats to its existence, remains a key to Mojave Desert tortoise survival into the future.

Funding to purchase and make this educational production accessible was provided by the U.S. Department of Education:

PH: 1-800-USA-LEARN (V) or WEB:

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The United States Geological Survey (USGS) conducts research on the desert tortoise in the Mojave Desert with the hopes of allowing the species to recover and escape the threat of extinction.

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