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Mojave Desert

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Winter at the Desert Tortoise Conservation Center

Snow dusts the Spring Mountains.

Spring Mountains, to the west of the DTCC, dusted in a layer of light winter snow in December 2009.

In the winter, the Mojave Desert can feel pretty deserted—the plants die back significantly, there are no insects buzzing in the sky, very few birds can be seen, the mammals and reptiles seem to disappear, and the air is quiet.

At the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC) it is hard to imagine we have so many tortoises on site because all of them are underground sleeping in burrows.

This winter hibernation, called brumation for tortoises, is actually very important for the health of the desert tortoise, because it allows for substantially reduced metabolic activity and aids in normal growth patterns during the active season by providing a period of little or no growth in the winter. Temperatures can drop below freezing during the winter here, so to protect themselves, tortoises dig natural burrows that are often curved, providing wind and rain breaks.

Volunteer Kelly Garron constructing a berm in front of an artificial tortoise burrow.

Volunteer Kelly Garron constructing a berm in front of an artificial tortoise burrow.

Often tortoises will backfill the area around them at the deep end of their burrows, providing even more protection from the elements. But for tortoises that are currently living in our quarantine area at the DTCC because they are relatively new arrivals, we dig artificial burrows that are angled deep beneath the surface of the earth (12 to 36 inches or 30 to 91 centimeters, depending on the size of the tortoise). Since artificial burrows do not have curves like natural burrows do, we provide these tortoises with added protection from the elements by creating a berm (mound) of soil at the mouth of the burrows that the tortoises can easily knock down when they are ready to emerge in the spring.

Many people think of the desert as a hot, dry place, and for much of the year it is; however, during the winter the average highs are in the 50s while the lows are in the 30s. Chilling, seemingly relentless winds whip through the desert frequently and can exceed speeds of 40 mph. In December 2009, just last month, we saw snow at the DTCC! It didn’t stick, but the Spring Mountains to our west were dusted in a light blanket.

At this time of year we also receive roughly 2 inches (5 centimeters) of rainfall, which is pretty impressive considering that the Las Vegas area averages less than 5 inches (13 centimeters) per year! In 2010, we have had 0.29 inches (0.7 centimeters) of rain so far, but most of our rain usually falls in February (according to National Oceanic and Atmospheric Administration), so we are hopeful winter rains will be plentiful here. The winter rains are vital to the spring bloom, which can be very impressive, and they also support much needed food and water sources for tortoises when they come out of hibernation.

So while we finish berming tortoises in for the winter to keep them safe and protected, we will hope for more rain and a beautiful spring bloom to report!

Kirsten Dutcher is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center. Read her previous post, Reptile Diversity at Desert Tortoise Conservation Center.

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Reptile Diversity at Desert Tortoise Conservation Center

Long-nosed leopard lizard

Long-nosed leopard lizard

The Desert Tortoise Conservation Center (DTCC) is located in southwest Las Vegas on a lovely patch of bajada (a broad sloping area of the desert surrounded by mountains). Here in the heart of the Mojave Desert, we are home to many desert tortoises, which are considered a flagship species in this ecosystem. That means the tortoise is an important representative of the Mojave Desert, and conservation and education efforts that relate to this species will benefit the entire ecosystem. The desert tortoise is the only chelonian (turtle/tortoise) in our area of the Southwest, but the Mojave is also home to a great many plant and animal species, including approximately 40 lizard and snake species, many of which use desert tortoise burrows as protection from predators and harsh environmental conditions. As a result of this relationship, many of these animals are found naturally right here at the DTCC.

Desert horned lizard

Desert horned lizard

Some reptile species that we see regularly include the desert horned lizard Phrynosoma platyrhinos. These lizards are incredibly cute! Luckily, they are also very well adapted to desert life. When frightened, they stay very still and often resemble rocks, so be careful to watch out for one when driving down desert roads, and remember to slow down because they are incredibly hard to see. The desert horned lizard, like all horned lizards, eats ants. Like some other reptiles, they can be very difficult to care for properly in captivity, but they continue to be popular as pets because they are so cute. But these animals belong in the desert, and that’s the only place they can truly thrive, so remember: wildlife should never be removed from the wild. Every individual that is taken into captivity as a cute little pet is one less individual that is available to support native populations. Once an individual is removed from the desert, it is considered biologically dead, since it is no longer breeding and filling its natural role in the wild.

Another amazing lizard we find on site is the long-nosed leopard lizard Gambelia wislizenii, pictured above. These beautiful lizards are fairly fast and quite good hunters. They survive by eating insects, spiders, other lizards, snakes, rodents, and occasionally plant matter. They often use a sit-and-wait style of hunting, but are capable of becoming bipedal (standing on two legs) when they run fast. The amazing colors seen on the female pictured here are typical during the spring breeding season; however, at other times of the year leopard lizards lose the orange coloration.

Mojave green rattlesnake

Mojave green rattlesnake

In terms of venomous snakes, we are incredibly fortunate here in the Mojave because we have just a few species. Our most dangerous venomous snakes are rattlesnakes, which look very different from Colubrids (mildly or non-venomous species that kill their prey by constriction). The Mojave green rattlesnake Crotalus scutulatus and sidewinder Crotalus cerastes are two species of rattlesnake we have seen regularly at the DTCC. Like all rattlesnakes, they do not lay eggs but give birth to live young! The sidewinder is very small and often nocturnal, while the Mojave green is considerably larger and can be found during the day or night if environmental conditions allow. The rattlesnakes offer no threat to the tortoises and at times can be found taking shelter in their burrows!

In addition to these snakes, the Mojave Desert supports three species of rear-fanged venomous snakes: the lyre snake Trimorphodon biscutatus, the night snake Hypsiglena torquata, and the southwestern black-headed snake Tantilla hobartsmithi. All snakes should be treated with respect, as should all wildlife, so it is best not to approach them. Humans have experienced adverse reactions to their bites, but no deaths have been reported.

These animals, and many others, are found right here at the DTCC and in the surrounding desert. The Mojave is truly an amazing place, with a subtle and quiet beauty that is often overlooked. Apart from being a spectacular desert of incredibly extreme conditions, it is also rich with highly specialized plants and animals. Saving the desert tortoise is not just about protecting the tortoise; it also preserves the habitat in which the tortoise lives, thereby protecting many other plants and animals from the threat of extinction. If we lose our desert tortoises, we will lose the Mojave Desert ecosystem as well, so thanks to all of you who support our efforts!

Kirsten Dutcher is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center. Read a previous post about the DTCC, Desert Tortoise: Hatchling Surprise.