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| Crunch, crackle. Crunch, crackle. What’s going on under that creosote
bush? Push aside the branches, peer into the shade, and you may catch
a glimpse of the animal I observed while hiking in the park last spring:
a desert tortoise, Gopherus agassizii, California’s state
reptile. |
| These unhurried creatures make their home throughout the park, except
in the steepest areas. Just how fast does a tortoise walk? (Answer at the
end of this article). If you see one you are fortunate: these animals spend
almost 95 percent of their time underground! |
| Arguably the most-studied animal in the park, the tortoise was placed
on both the California and Federal Endangered Species Lists in1989 and 1990,
respectively. Its status is “threatened,” just one notch below
“endangered.” Several factors conspired to diminish the population
of the desert tortoise. As more people moved into the western deserts, the
resultant loss of habitat made a serious dent in the number of tortoises.
With more people came more ravens, large black birds with a keen appetite
for hatchling tortoises. The number of ravens has exploded in recent years,
due in large part to their ability to thrive in developed areas. The factors
contributing to their dramatic increase include more roads, thus more roadkill;
landfills; powerline poles, an ideal lookout post for hungry ravens; and
littering. Litter in the park attracts ravens, so please dispose of your
garbage responsibly. |
| Perhaps because of the release into the wild of former pet tortoises during
the past several decades, a deadly bacterial infection began to appear more
and more frequently among wild tortoises. Upper Respiratory Tract Disease
attacks the tortoise’s respiratory system and can be transmitted through
sharing of burrows, or through human handling of tortoises. This can occur
when a person handles a sick tortoise and then unwittingly transmits the
disease to a healthy animal. Other means of transmission may include common
tortoise behavior such as head-bobbing, circling one another, chin gland
sniffing, and biting. |
| These are the tortoise’s versions of shaking hands, hugging, exchanging
pleasanteries, and courting. If the greeters are both males, they sometimes
proceed to more rough-and-tumble behavior. Using the extended portion of
the underside of the shell, or gular horn, males will engage in a form of
jousting where the purpose is to flip the opponent. If this happens the
overturned tortoise must right itself soon, or it will die from suffocation,
exposure to the sun, or freezing. |
| Females generally behave less aggressively than males, and may spend more
time underground since it is their task to nest and produce clutches of
eggs. Females have, however, been observed aggressively defending their
nests from the unwelcome presence of other reptiles and even park biologists!
Tortoises may mate at any time of year, with the peak season from March
through early October. A female may retain viable sperm for up to eight
years after mating and still lay fertile eggs at that point. The average
number of eggs per clutch is five, and they are usually laid from May through
July. Several clutches may be laid annually, depending upon the availability
of food and water. Eggs hatch anywhere from 70 to 120 days later. The chromosomes
do not determine the sex of the offspring. Rather, the incubation temperature
produces males or females. |
| It is estimated that desert tortoises have existed for 15 to 20 million
years. Perhaps this long stint on Earth has given them plenty of time to
consider wise living strategies, such as careful, slow-paced locomotion;
a healthy diet full of greens; resting during winter and summer, the desert’s
most challenging seasons; and water conservation. The typical tortoise diet
consists of grasses, wildflowers, cactus pads, and wild fruit. Occasionally
a tortoise will eat bone material scavenged from mammal scat as a means
of obtaining calcium. Its stumpy, elephantine legs end in sharp claws, which
are adapted to walking in sand and to digging dens or burrows used for both
hibernation and estivation (summer “hibernation”). Tortoises construct
dens up to 30 feet in length—in general, summer burrows are shallower
and shorter. Because they are cold-blooded, tortoises are not able to regulate
their body temperature internally. Burrowing is an adaptation that mitigates
the effects of the desert’s temperature and moisture extremes, and
protects animals from predators. Desert tortoises also dig depressions in
the earth to catch rainwater. They are able to store water in their urinary
bladder and significantly increase their body weight when tanking up after
a good rainstorm. |
| If you see a tortoise in the wild, it is important not to pick it up.
Like a young child who may wet his pants when afraid, a tortoise will “void”
its bladder if frightened. This could have life-threatening consequences
for the animal if it is not able to replenish its water supply. Handling
wild tortoises is illegal under the Endangered Species Act. The only reason
for picking one up is when the tortoise is on or near a road and is in imminent
danger of being struck by a vehicle. If you must move one, grasp it firmly
with two hands, keep it just a few feet above the ground, and place it gently
on the ground (preferably in the shade) in the same direction in which it
was headed. |
| It is illegal to remove a tortoise from the wild and bring it home as
a pet. There are plenty of rescued tortoises looking for good homes. If
you are interested in adopting one, please contact one of the park’s
visitor centers or a chapter of the California Turtle and Tortoise Club.
Do not release pet tortoises into the wild; they may carry a number of diseases.
Even if a domesticated tortoise appears healthy it probably will not be
able to fend for itself after being dumped in the desert. It is used to
being cared for, and may have lost its instincts to forage and protect itself
from predators. Beyond that, tortoises are highly territorial and an intruder
will not be tolerated for long. Tortoises have good vision and a good sense
of smell, and they know their territory well. During its lifetime of 50
to 100 years, a wild tortoise rarely moves more than a couple of miles from
its birthplace and is intimately familiar with the resources within its
territory. These resources are vital to its survival, and may not support
a new addition. |
| The aboriginal peoples who lived in the western deserts were well acquainted
with the tortoise. Although not all groups would eat tortoise meat, it was
generally prized for its food value. Some hunters lured tortoises onto the
surface of the ground by placing a dish of water at the opening of a burrow.
Tortoises were then roasted in cooking pits lined with hot rocks. The shells
were put to a variety of uses: they served as bowls, scoops, spoons, ladles,
and were sometimes ground into powder for medicinal purposes. They were
also used to make ceremonial rattles: the carapace, or upper dome-shaped
half of the shell, and the plastron, or flat underside of the shell, were
joined together after being filled with small stones or seeds. The openings
at either end were plugged with pitch. Tortoise motifs appear in desert
rock art and in basketry and pottery. Several creation stories feature a
tortoise shell, whose shape evokes the dome of the sky above the earth.
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| Biologists are currently studying the desert tortoise living within Joshua
Tree National Park. Using measurements collected by such sophisticated equipment
as radio telemetry and GPS (Global Positioning System), they are gathering
information that allows us to increase our understanding of this threatened
desert reptile. |
| Spring is a good time to spot a desert tortoise because the warm temperatures
trigger an impulse to emerge from the burrow, forage, and look for mates.
If you see one, please fill out a wildlife observation card, available at
visitor centers and entrance stations. By slowing your pace, you will increase
your chances of catching a glimpse into the unassuming world of the desert
tortoise. |
| (Answer: average speed is 0.2 mph) |
| by Park Ranger Caryn Davidson |
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last modified: 03/21/02
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