DESERT TORTOISE: CHARACTERISTICS, HABITAT, REPRODUCTION - BIOLOGY - 2025

The desert tortoise (Gopherus agassizii) is a reptile that belongs to the Testudinidae family. Among its characteristics is the carapace, which has grayish brown or blackish brown shields. Usually the center of these is orange or yellow.

This carcass protects the animal from predators, but also from strong solar radiation. Thus, the temperature of the shell is usually between 8 and 10 ° C higher than the body temperature.

Desert turtle. Source: US Fish and Wildlife Service

This species is found in California, southern Nevada, western Arizona, and southwestern Utah. In Mexico, it is found mainly in Sonora, Sinaloa, and the Gulf of California. Its habitat includes slopes where creosote plant cover and sandy soils abound.

As for the senses, smell is one of the most important in the desert tortoise. Olfactory stimuli are used for feeding, courtship and other social interactions.

Evolution

The ancestors of tortoises possibly crossed the Bering Bridge, thus reaching North America. On this continent, during the Oligocene and Miocene, there were around 50 species of tortoises, many of which were giants.

In the Pliocene, the large species became extinct throughout most of their home range. On the other hand, according to the fossil records, the Testudinidae family appeared during the Middle Eocene.

Genus Gopherus

As for the genus Gopherus, it may have evolved from an early species of the genus Stylemys, in the late Eocene epoch. The earliest known species are the Gopherus laticunea and the Gopherus praextons, which dates back 45 million years.

The separation of the Gopherus groups may have occurred during the late Pleistocene. During this period, unfavorable environmental conditions caused the separation of western populations from eastern ones.

Regarding the geographic extension of G. agassizii to New Mexico, Arizona and Texas, it probably occurred in the late Pleistocene.

Habitat

During the Eocene, most tortoises lived in subtropical or tropical regions. In relation to the Eocene-Oligocene transition, it is associated with various climatic and vegetative variations. Because of this, the plants probably underwent a change, they were thicker and xeric.

The Oligocene period is characterized by continental elevations. Thus, at that time, the excavation behavior of the Gopherus suggests the existence of a semi-arid habitat, with regions of thorn scrub and chaparral, On the other hand, in the Upper Pliocene, the climate and vegetation was changing. At this time of prehistory, due to glaciation, the range of the Gopherus shifted south.

These environmental conditions caused the division of the desert tortoise into two populations, one eastern and one western, G. berlandieri and G. agassizii, respectively.

According to investigations, G. agassizii may have used the southern corridor of the Rocky Mountains as one of the routes to disperse.

General characteristics

Gopherus agassizii at Buffalo Zoo

Skin

The skin on the head and limbs of the desert tortoise is thick and reddish-brown or blackish-gray. The skin on the neck and in the socket of the extremities is yellowish.

Shell

This structure is oblong and slightly flat dorsally. As for its length, it measures between 215 and 335 millimeters. The shields are tan, grayish brown, or blackish brown in color. These often have a yellow or orange center.

It has a high dome, which allows more space for the lungs. In almost all species, the carapace is made up of 50 bones.

In relation to the shields, it consists of a nuchal one, with eleven marginals on each side. The last of these joins to form a supracaudal plate. Also, it has five neural or vertebral shields and four costals, where the first is the longest and the last the smallest.

Plastron

The desert tortoise has a yellow plastron, with the edge of the blades brown. It is made up of nine bones: 2 hypoplastron, 1 entoplastron, 2 epiplastron, 2 xiphiplastron, and 2 hyoplastron.

The fontanelle closes completely when the plastron is about 210 millimeters long. As for the shields, it has 6 pairs. The pectorals are smaller than the abdominals and have a shorter median suture. Humeral plates are larger in dimension than femoral plates.

Skeleton

The skeletal system includes eight cervical, twelve dorsal, and eight cervical vertebrae. The caudal vertebrae can have a variable number. This species has a very pronounced interclavicular keel, which widens the area of ​​origin of the deltoid muscles.

In relation to the ribs, the first and second are fused to the costal plates. From the third to the eighth they are attached to the dorsal shields. The sacral ribs are associated with the dorsal ends.

Extremities

The hind limbs are rounded, thick, short and have four fingers. The front ones are flattened, scaly and have five digits. These limbs are used to dig burrows and nests.

As for the fingers, they have strong and wide claws. Furthermore, they cannot move independently, since they are very short and due to the flattening of the articular surface between the metacarpus and the proximal phalanges.

Head

Pierre Fidenci

The head of the Gopherus agassizii is small. The eye has a greenish-yellow or yellow iris with a brown outer edge. In relation to the jaws, they are serrated. Thus, they are adapted to crush the plants they consume.

Beneath the bulbs of the jaws there are two glands known as the chin or subdental glands. In the male it is well developed, especially during the breeding season. However, in the female these structures may not be functional.

The function of these glands is related to visual and olfactory signals, used during courtship. Male secretions contribute to sexual recognition. In addition, males can respond aggressively to other turtles that have the same substances.

The subdental glands have an external epithelial tissue without scales and two or three external openings. The substance they excrete is made up of free fatty acids, triglycerides, esterase and cholesterol.

Gular horn

In both sexes, the plastron has an extension in the anterior region. This structure is known as the gular horn and in the male it is longer and curved upwards.

It is used by the male in his combat with other males. Thus, he tries to insert it under the front edge of the opponent's armor, turning it to the side to try to turn it on its back. To avoid this, the opponent tries to keep his body up.

Sexual dimorphism

In this species, the sexual dimorphism is very marked. For example, the male has thicker claws and the tail is longer, which makes it easier for the penis to be inserted into the female's cloaca during copulation.

Furthermore, the male's plastron is concave, especially towards the femoral area. This allows it to conform to the female's shell during mating.

Habitat and distribution

Lake Mead NRA Public Affairs

Gopherus agassizi is distributed to the west and north of the Colorado River, in the southwestern United States, and in the Sonoran and Mojave deserts of California. It is also northeast of Arizona, southern Nevada, and southwest Utah.

The desert tortoise lives most of the time underground, in burrows that provide it with a cooler temperature than outside. This way you can escape the arid desert conditions.

It usually inhabits from rocky hills to sandy plains, including canyon bottoms, semi-arid grasslands and gravel deserts, where it can dig its burrow. In addition, it can be found both in areas very close to sea level and in ecosystems located 915 meters high.

Regions

This species lives in different regions. In the south, encompassing northern Sinaloa and southern Sonora, it lives in tropical deciduous forests and thorn scrub. However, to the north, it is located in the desert and deciduous thickets of the Sonoran desert.

Its habitat is usually grouped into three large groups of populations. The tortoises that live in the Sonoran desert are located on alluvial slopes and in the valleys of the desert mountain ranges.

In this area, the rains are regular and cacti and the dandelion species abound. Also, it inhabits rocky and steep slopes, with populations of saguaro and palo verde cacti.

In the Mojave Desert, southeast California, southern Utah, and southern Nevada, it is distributed in valleys where juniper forests and clay soils abound, where it can easily dig. Also, it prefers creosote bushes, white bursage, and grass.

On the other hand, to the south, the Sinaloa desert tortoises are found in thorn thickets and in tropical deciduous forests.

Home range

In females, the average home range is 2.6 to 23.3 hectares, while for males it is 9.2 to 25.8 hectares. This species is not territorial, so the areas can overlap.

Those that live in the desert generally expand their area in the summer and spring months, when they are most active. During the winter or in very dry and hot seasons, the reptile remains in its underground burrow.

Burrows

Gopherus agassizi burrows in sandy soil, dry gravel, or at the base of a bush. This is shaped like a semicircle and generally measures between 92 and 275 centimeters.

Burrows are built for various purposes. Thus, those in spring are shallow, since, during that time of year, the desert tortoise can rest under the shade of a bush.

In relation to the summer ones, they are usually short, while the winter shelter is longer and is often dug in the upper zone of a steep bank.

Taxonomy and classification

-Animal Kingdom.

-Subreino: Bilateria

-Filum: Cordate.

-Subfilum Vertebrate.

-Superclass: Tetrapoda.

-Class: Reptilia.

-Order: Testudines.

-Suborder: Cryptodira.

-Superfamily: Testudinoidea.

-Family: Testudinidae.

-Gender: Gopherus.

-Species: Gopherus agassizii.

State of conservation

Desert tortoise in southern Nevada

In recent years, populations of desert tortoises have suffered a significant decline. This situation has led the IUCN to classify Gopherus agassizi as a species vulnerable to extinction.

Likewise, in 1990, the United States Fish and Wildlife Service classified this reptile within the endangered group. In 1994, Mexico declared the desert tortoise threatened.

Threats

One of the main factors that afflict this species is the loss of its habitat. Man has cut down and modified the environment where this turtle develops. This has resulted in the expansion of the urban area and the creation of new agricultural spaces.

In addition, the construction of the roads has caused the vehicles that pass by to kill the turtles that try to cross the road. Another threat is the loss of forage plants. This is due to their replacement by invasive species and by competition with livestock for grazing.

The urban development of the desert causes an increase in the sources of water and food, including the garbage they produce. This brings as a consequence that the native crows get closer, which represents a serious threat from this predator towards the turtles.

Also, this reptile is captured to be sold as a pet. In addition, it is vulnerable to attack by wild dogs, foxes, coyotes, and badgers.

Actions

The Gopherus agassizi is included in Appendix II of CITES. This species is under the protection of federal and state agencies. These agencies have developed programs oriented towards the recovery of the populations.

In addition, sanctuaries have been created, where, among other conservation actions, entry to vehicles is prohibited. The management plan includes the monitoring of the communities and the construction of fences or elevations, which keep this reptile off the roads.

Reproduction

During the reproductive life of the desert tortoise, which begins between 15 and 20 years, it could have several pairs. In addition, in this period, the male has a high level of testosterone, with higher values ​​than the vast majority of vertebrates.

Before mating, males fight each other to gain access to a female in heat. In combat, males shake their heads, clash their shells, and chase each other.

Often during fighting, they try to turn around, using their gular horn. If one succeeds, the loser straightens up and leaves the place. After this, the winning male courts the female. To do this, he surrounds her and prevents her movement, hits her and tries to bite her.

During mating, desert tortoises vocalize prolonged moans and grunts. In addition, the striking movements between the shells emit a sound similar to that of a drum.

Once the female has mated, she can store the sperm in her reproductive tract. Seminal fluid may remain viable for about 18 months after intercourse.

Nesting

Depending on the physical condition and age of the female, she can lay up to 3 clutches per year. In each litter, it lays between 2 and 14 eggs. Some time before laying the eggs, the female selects the site where she will build the nest. This is usually located near the resting place or the burrow.

After he digs the hole, he urinates it. This behavior could be associated with the intention to ward off predators or to try to keep the eggs moist. Once they are in the nest, it covers them with dirt and urinates again.

The female tends to protect the eggs for a time, preventing some of the natural predators, such as the crow, eagle, and fox, from consuming them. Once hatching occurs, around 90-120 days after nesting, the mother abandons the young.

Soil temperature can influence the development of the embryo. Experts point out that, in the lowest temperatures, between 26 and 29 ° C, the vast majority of the young are male. On the other hand, if during incubation the temperature is between 30 and 32 ° C, females will abound in the herd.

The babies

The young use the egg tooth to break the shell. At birth, they have a yolk plug, which provides them with food. Regarding its size, it measures 4.5 to 5 centimeters long and weighs approximately 20 to 27 grams. Their shell is soft and will stay that way for about five years.

Its coloration is brown, with the center of the shields of a dull yellow tone. In relation to its skeleton, it is incomplete. In addition, it has a fontanel on each side of the carcass and between the pair of ribs.

The dry yolk sac remains attached to the umbilical area of ​​the plastron, but is absorbed two days after hatching.

Feeding

The Gopherus agassizzi is a selective herbivore, which modifies its diet according to the availability of the plants. Thus, choose succulents until the last days of spring, when the vast majority of herbaceous and annual plants are dry.

Their diet consists of leaves, flowers, stems, roots, barks, and fruits. These come from shrubs, trees, succulents, woody vines, cacti, herbaceous annuals and perennials. Occasionally, it may eat carrion or some insects.

Among the preferred species are Cassia armata, Euphorbia sp., Eriogonum sp., Opuntia basilaris, Erodium cicutarium, Bouteloua barbata, Festuca octoflora and Bromus rubens. Within the group of perennial grasses is Hilaria rigida, Oryzopsis hymenoides and Muhlenbergia porteri.

The most important time, as far as nutrition is concerned, is spring. In this period, desert tortoises require green vegetation, which allows them to replace the fat reserves that were used during hibernation. In relation to summer, perennial herbs are important, due to their succulence.

On the other hand, the natural habitat of this reptile is characterized by long periods of drought. Due to this, the animal obtains the water it requires from vegetation and temporary ponds.

Feeding method

This species has adaptations that allow it to feed "tongue". These include a large, movable tongue and a serrated chewing surface. Also, it has an arched palate and a marked cranial flexure. This allows the animal to breathe freely when the mouth is closed.

The desert tortoise forages as it wanders from one plant to another, sniffing the plant before eating it. When selecting a grass, she cuts it down to ground level and swallows the piece, after a few chews.

In addition, it can raise its body, leaning on its strong hind legs. In this way you can access the pods and branches of the Lotus sp.

Behavior

Pierre Fidenci

The Gopherus agassizi is most active during the months of March to September. During the first months of summer and in the spring they spend most of their time feeding on the native grasses of the area. From late fall through winter, they retreat to their winter lair.

This species faces another problem, the scarcity of water. To maximize the small amount of water produced by rain, this reptile digs catchment basins in the ground. Because he can remember the place, he often goes to drink water from these.

In addition, to survive, the desert tortoise concentrates and stores urine in its bladder. In this way, the body can extract the water it contains, as needed. In very dry times, your urine can have a pasty and white consistency, due to the low amount of water and the high salt content.

Vocalizations

Each species can emit vocalizations that characterize it, in this way these sounds can be used to identify it. Some of the calls are moans, hisses, weak meows, and screams.

Calls are common during fighting and in mating. They also often use them while looking for food. Specialists maintain that the frequency and complexity of these increase with age.

References

1. Grover, Mark C., DeFalco, Lesley A. (1995). Desert tortoise (Gopherus agassizii): statusof-knowledge outline with references. Gen. Tech. Rep. INT-GTR-316. Ogden, UT: US Department of Agriculture. Recovered from fs.fed.us.
2. Crozier, G. (1999). Gopherus agassizii. Animal Diversity. Recovered from animaldiversity.org.
3. com (2019). Mohave Desert Tortoise - Gopherus agassizii. Recovered from californiaherps.com.
4. Tortoise & Freshwater Turtle Specialist Group (1996). Gopherus agassizii. The IUCN Red List of Threatened Species 1996. Recovered from iucnredlist.org.
5. Bryan Jennings, Kristin H. Berry (2015). Desert Tortoises (Gopherus agassizii) Are Selective Herbivores that Track the Flowering Phenology of Their Preferred Food Plants. Recovered from journals.plos.org.
6. Bryan Jennings (1997). Habitat Use and Food Preferences of the Desert Tortoise, Gopherus agassizii, in the Western Mojave Desert and Impacts of Off-Road Vehicles. Recovered from tortoise-tracks.org.
7. Lovich, J.; Daniels, R. (2000). Environmental Characteristics of Desert Tortoise (Gopherus agassizii) Burrow Locations in an Altered Industrial Landscape. Chelonian Conservation and Biology. Recovered from tethys.pnnl.gov.