
The California desert is home to a variety of wildlife, but can turtles survive in this hot, arid environment? The Mohave Desert Tortoise (Gopherus agassizii) is a species native to the Mojave and Sonoran Deserts of the southwestern US and northwestern Mexico. It is California's state reptile and can be identified by its large unwebbed limbs, high-domed shell, and elephant-like skin. Spending 95% of its time in burrows, rock shelters, and pallets, the desert tortoise is well-adapted to the harsh desert climate.
What You'll Learn
Desert tortoise habitat
The desert tortoise (Gopherus agassizii) is a species native to the Mojave and Sonoran Deserts of the southwestern US and northwestern Mexico. They are the official state reptile of California and Nevada.
Desert tortoises inhabit elevations from below sea level in Death Valley to 1,600m in Arizona, though they are most common from 300m to 1,050m. They are sensitive to soil type, as they rely on their burrows for shelter, water loss reduction, and body temperature regulation. They prefer sandy loam soils with varying amounts of gravel and clay and tend to avoid sands or soils with low water-holding capacity.
The recommended area for a tortoise habitat is 600 square feet, with some areas of shade and some of full sun. The area must be fenced, with a one-foot clear space around the edge of the habitat for the tortoise to walk. The habitat should include a burrow with a covered water dish and a variety of plants for the tortoise to browse. The burrow should be located in a completely dry area, with the opening facing south, southeast, or southwest to avoid the hot summer sun. It should be at least five feet from walls, sidewalks, and plants on all sides.
Desert tortoises are well-adapted to living in highly variable environments. They spend 95% of their lives in their burrow, emerging to feed and mate during late winter and remaining active through the spring. They may emerge again after summer storms. They are long-lived, surviving from 50 to 80 years, and have a low reproductive rate.
The main causes of mortality in desert tortoises include predators, human-related causes, diseases, and environmental factors such as drought, flooding, and fire. The most significant threats to tortoises include urbanization, disease, habitat destruction, illegal collection, and habitat conversion from invasive plant species.
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Human impact on tortoise populations
Human activities have had a significant impact on tortoise populations in California, particularly the Mojave desert tortoise (*Gopherus agassizii*), which is California's state reptile. Here are some key ways in which human actions have affected these tortoise populations:
- Habitat Loss and Fragmentation: The expansion of human settlements and the development of housing and renewable energy projects have led to the destruction and fragmentation of tortoise habitats. This loss of suitable habitats has made it challenging for tortoises to find food, regulate their body temperature, and protect themselves from predators.
- Road Construction: Roads not only fragment tortoise habitats but also pose a direct threat to tortoises due to vehicle collisions. Additionally, roads contribute to the increase in raven populations, as these birds scavenge on roadkill and use power lines as lookout posts for hunting.
- Off-Road Vehicle Use: The use of off-road vehicles in tortoise habitats can crush and kill tortoises, destroy their eggs and burrows, and facilitate the spread of invasive grasses, further degrading their environment.
- Disease Introduction: The release of former pet tortoises into the wild has likely contributed to the spread of diseases, such as Upper Respiratory Tract Disease, which can have devastating effects on wild tortoise populations.
- Illegal Collection and Trade: The capture and trade of wild tortoises are illegal in California. However, the demand for tortoises as pets or for other purposes continues to threaten wild populations.
- Vandalism and Shooting: Human activities such as vandalism and shooting of tortoise shells have also been reported, causing direct harm to tortoises and potentially attracting predators like ravens.
- Invasive Species: Human activities can introduce invasive plant species, such as grasses, that can degrade tortoise habitats. These invasive grasses, combined with fires, can turn deserts into non-native grasslands, making it challenging for tortoises to survive.
- Littering: Littering in parks and natural areas can attract ravens, which feed on tortoise hatchlings.
The cumulative impact of these human activities has led to a significant decline in tortoise populations, with some areas reporting up to a 90% decrease since the 1980s. As a result, the Mojave desert tortoise is now listed as "threatened" under the Endangered Species Act, and efforts are being made to protect and conserve these ancient creatures and their habitats.
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Tortoise diet and eating habits
The diet and eating habits of tortoises vary depending on the species. For example, the diet of a tortoise in the wild is different from that of a captive tortoise.
Wild Tortoise Diet
Wild tortoises are herbivores and primarily graze on a wide variety of leafy vegetation, grasses, shrubs, cacti, leaves, fruits, and even carrion. They have also been observed eating the bones of mammals to obtain calcium. They feed on around 200 different species of plants in a year, ensuring they have the correct balance of essential minerals and trace elements needed for growth and healthy bone development.
Tortoises are slow eaters and can take several days to consume a meal. They are also able to survive on very little food and water for long periods of time. They can increase their body weight by up to 40% after drinking water, and adult tortoises can survive a year or more without it.
Captive Tortoise Diet
For captive tortoises, it is important to know the specific dietary requirements of your species of tortoise. Generally, tortoises in captivity should be fed a well-balanced and varied diet of fresh leaves and vegetation. Home-grown leaves and edible weeds are preferable to bought fruit and vegetables due to their higher nutrient content.
Hatchlings and young tortoises should be fed daily, while adult tortoises can be fed daily or you may choose to omit feeding for one day a week. It is easy for captive tortoises to overeat, which can lead to shell growth deformities and other health problems. Therefore, it is important to monitor their growth and adjust their food intake accordingly.
Fruit should be offered only in small amounts and infrequently, as the digestive system in most tortoises is not geared towards digesting fruit. Additionally, vegetables such as peas and beans, which are high in protein and phytic acid, should be avoided where possible. Root vegetables, such as carrots or parsnips, should be limited or not fed at all.
A mineral and vitamin supplement can be added to the food a few times a week. Fresh drinking water should always be available.
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Tortoise mating and reproduction
Mating and reproduction in tortoises is a complex process that involves courtship, mating, egg-laying, and hatching. While scientists have only recently begun to understand tortoise reproduction, there are still many unknowns.
Courtship
Courtship techniques vary between tortoise species, but they all have one thing in common: male aggression. Male tortoises will bite females, ram into them with their shells, and circle around them in an intimidating manner. Some male tortoises may also lift up the shells of female tortoises to prevent them from escaping. This is accompanied by behaviours such as sniffing and head-bobbing.
Mating
Male tortoises approach females and may chase, nip, or sniff them. The male then mounts the female, with his forelegs propped up on the front of her shell. The male may also produce grunting noises and move his front legs up and down in a constant motion.
Egg-Laying
Female tortoises will dig a nest, usually in the afternoon or early evening, using their front legs to clear the area and their rear legs to dig out the soil. The nest is typically about three-quarters of the length of the female's shell deep. The female will lay her eggs one by one, taking care to roll each egg to the side of the nest to prevent cracking. The number of eggs laid depends on the size of the female, with a typical clutch ranging from 4 to 8 eggs.
Hatching
The incubation period for tortoise eggs varies depending on the species, ranging from 70 to 175 days. The temperature of the nest affects the sex ratio of the hatchlings, with higher temperatures resulting in more females and lower temperatures resulting in more males. In the wild, natural sunlight and moisture from the earth keep the nest at an optimal temperature.
Reproductive Readiness
Reproductive readiness in tortoises is determined by size rather than age. Females are typically ready to breed when the length of their carapace (upper shell) is about 7 to 8 inches. Wild tortoises may be 15 to 20 years old before they breed, while well-fed pets may reach reproductive maturity in half that time.
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Tortoise lifespan
Tortoises are known for their longevity, with an average lifespan of between 50 and 150 years, and some living for nearly two centuries. The specific species of tortoise impacts its lifespan, with some species living for only 10 to 20 years in captivity, while others can live up to 150 years. The tortoise's lifespan is also influenced by factors such as captive care, genetics, and environment.
The desert tortoise (Gopherus agassizii), native to the Mojave and Sonoran Deserts, has a lifespan of 50 to 80 years. They spend most of their time in burrows, rock shelters, and pallets to regulate body temperature and reduce water loss, which contributes to their longevity. Their ability to tolerate water, salt, and energy imbalances on a daily basis also increases their lifespan.
In captivity, most tortoise species can live well into their 50s if provided with appropriate care, including a balanced diet, shelter, and veterinary attention. However, improper care, such as an inadequate environment and nutrient-deficient diet, can result in sick tortoises with extremely short lifespans.
Tortoises in the wild face various challenges that can impact their lifespan, including predators, human-related causes, diseases, and environmental factors such as drought, flooding, and fire. Their slow reproductive cycle and low survival rate of hatchlings also contribute to their long lifespans.
Overall, tortoises are known for their impressive longevity, and with proper care, they can live for several decades, and sometimes even over a century.
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Frequently asked questions
The desert tortoise (Gopherus agassizii) is a species of tortoise native to the Mojave and Sonoran Deserts in the southwestern US and northwestern Mexico. It is California's state reptile.
Desert tortoises live in underground burrows in the Mojave and Sonoran Deserts. They spend 95% of their time in these burrows, as well as in rock shelters and pallets, to regulate their body temperature and reduce water loss.
Desert tortoises are herbivores and eat grasses, flowers, fruit, and cactus. They can go for up to a year without access to fresh water.
Desert tortoises can live for 50 to 100 years.
It is illegal to capture a desert tortoise from the wild. However, they can be kept as pets if they are acquired from another private owner.