||Tortoises have lived in the area that is now the Mojave
Desert for millions of years, even before it was a desert.
The Mojave desert tortoise occurs north and west of the Colorado
River in California, Nevada, Arizona and Utah. As recently
as the mid-1900s, people commonly encountered these familiar,
gentle creatures. Today, they are rarely seen and in some
places they have disappeared entirely.
The Desert Tortoise is one of most elusive inhabitants
of the desert, spending up to 95% of its life underground.
The desert tortoise lives in a variety of habitats from
sandy flats to rocky foothills, including alluvial fans,
washes and canyons where suitable soils for den construction
might be found. It is found from near sea level to around
3,500 feet in elevation. Most desert visitors will not see
a tortoise. But if you plan your trip for early spring,
and are patient, you may see one of these popular residents
of the Mojave Desert.
The Desert Tortoise (Gopherus agassizii), has a high -
domed shell and elephant-like legs and is easily distinguishable
from its turtle cousins. They range in size from two inches
up to 15 for a mature male. The top shells are brown,
gray, or black, often with distinctive growth lines, while
the shell underneath is lighter.
Tortoises can completely withdraw their head and limbs
within their shells, leaving only horny scales visible to
predators. They have a short tail, and their claws aid them
in digging burrows. Males have longer curved gular horns
which protrude from their lower shells underneath their
neck and head. They use these horns to combat other males
and for butting and nudging females during courtship. Males
also have shallow depressions in their lower shells while
the females lower shell is flat. Most people cannot tell
the difference between male and female until they are between15
to 20 years old or eight inches in length.
The desert tortoise produces a variety of sounds (hisses,
grunts, pops, whoops, huhs, echs, bips, etc.) which seem
to be the most important when vocalized to an unfamiliarMay 3, 2013 series of head bobs
for species and gender recognition, courtship, and threat.
Head bobbing normally precedes combative behavior between
males, although females may also be aggressive.
Desert tortoises may live 50 or more years in the wild
and even longer in captivity. Their diet consists primarily
of wildflowers, grasses, and cacti.
A large urinary bladder can store over forty percent of
the tortoise's body weight in water, urea, uric acid, and
nitrogenous wastes. During periods of sufficient rainfall
tortoises drink from temporary rain pools. A common defensive
behavior when molested or handled is to empty the bladder,
leaving the tortoise at a considerable disadvantage during
dry periods. For this reason, desert tortoises should not
be handled when encountered in the wild.
Reproduction begins between ages 12-20, with clutch sizes
of 1-14 eggs. In years with low rainfall, females may lay
few to no eggs. Females can store sperm for five years or
longer, meaning they can reproduce for several years after
mating. Nests are built and eggs are laid in late spring
or early summer. The hatchlings appear in 90 to 120 days.
The mother leaves the nest, so once the hatchlings appear,
they must survive on their own.
Tortoises depend on bushes for shade and protection from
predators such as ravens and coyotes. To escape the temperatures
of cold winters and very hot summers, many tortoises live
in burrows. The spring and summer burrows vary from 18 inches
to five feet long, but may only be a few inches from the
surface. Winter burrows tend to be about eight feet long
and may be two to three feet from the surface. They often
share burrows and may use multiple burrows scattered across
the landscape. They hibernate for up to nine months each
year, becoming most active from March to June and September
to October. When they are young they seldom venture more
than 150 feet from their burrow. As they get older, they
may go as far as 3/4 mile in a day and use a network of
burrows. In the most densely populated areas, you may find
one tortoise per 2.5 acres. Typically, tortoise densities
are closer to one tortoise per 100 acres