desert tortoise

A desert tortoise cruising around in the Mojave Desert.

This cutey is a desert tortoise, a beloved species that is the state reptile of both California and Nevada. I ran into this individual with my herpetology class in the Mojave Desert, near the Zzyzx desert station. It was my first ever glimpse of a wild tortoise! Despite the fact that they are large and slow moving (they “run” at between .13 and .3mph), I considered myself quite lucky to get a chance to spot one. Because of the harsh desert climate that can reach up to 140° F (!!), the desert tortoise survives by digging underground burrows to escape the incredible heat. And still, from November through February, it can get really cold, so the tortoises remain dormant and protect themselves from freezing by living in burrows. These things together means that these tortoises will spend 95% of their life in a burrow. So seeing one out and about was quite a privilege, though we increased our odds by  choosing a good time of day and season.

desert tortoise

This picture shows two important features of the desert tortoise-its gular horn and its long digging nails. Image taken in the Mojave Desert.

This picture shows two important features of the desert tortoise. Notice the long nails on its feet for digging those oh so important burrows I was talking about. But they dig for another reason too.  As they live in an environment that has very little rainfall, water is incredibly scarce. These tortoises get most of their water from the vegetation they eat. But, they have an extra trick to get some extra water-they dig catchment basins in the soil. They will remember the location of the basins that they created and can even be found waiting by them when rain is near!

The second feature is its gular horn, which is the part of its shell poking out from under its head. Both sexes have a gular horn, but it’s larger on the males. Males will use these to fight other males by trying to flip their opponent onto their back. The males will fight at any time of year and usually the fight ends with one of the tortoises running away. Despite their fighting, where there are burrows that can hold several individuals, the tortoises will share. As soon as they leave the burrow, the males will begin fighting again, but protection from the extreme heat is just too important.

Aside from the extreme climate, desert tortoises have another struggle. Getting enough calcium for those shells, which make up approximately 80% of their skeleton, can be very difficult. Although they are herbivores, because of their need for calcium, they will occasionally chew on bones to help meet that need.

I mentioned earlier that these animals are beloved and I was serious. They have some pretty powerful friends. In particular, Dianne Feinstein has a fondness for the tortoise (in fact one of the desert tortoises at the San Francisco Zoo has the middle name “Dianne Feinstein” as a recognition for all of her tortoise support). Desert tortoises are listed as threatened both federally and by the state of California and they played a key roll in the passage of the California Desert Protection Act in 1994, which has just been updated this year to include more protections, again specifically because of the desert tortoise. The reasons for their declining populations are many, including the usual culprits. They live a really long time (60-80 years in the wild, longer in captivity.) and they are late to reproduce. When they are younger, for the first few years they have a soft shell and predation is a major problem; in particular an increase in the raven population due to an increase of food from people’s garbage has led to an increase in predation on tortoises. But one of the worst problems to date has been problems with pets. People collect the tortoises as pets and when they don’t want them anymore or when they outlive the original owner some folks have thought it a wonderful idea to release the former pets into the wild. This has led to the spread of a horrible respiratory disease that has been fatal to many wild tortoises. These tortoises are not good pets and because of their protected status, it is illegal to collect a desert tortoise. So remember:

 

desert tortoise sign

This sign is a reminder that it is illegal to even touch a wild desert tortoise. Image taken at Zzyzx research station.

If you are lucky enough to come across a wild desert tortoise, don’t touch it! It is illegal and can be fatal to the tortoise. These tortoises store extra water in their bladders, which can still be used, but if they are scared, they will sometimes release this excess water, increasing their likelihood of dehydration. With all of the natural problems they have to face, the last thing they need is avoidable human caused problems.

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