Hi everyone - I thought it was about time for an update on what I’m up to these days. After finishing up my internship with U.S. Fish & Wildlife Service last fall (see those blog entries here: Part 1, 2, 3, 4, 5), I accepted a position with the U.S. Geological Survey (USGS) working with Desert Tortoises (Gopherus agissizii) out in the Mojave. While USGS is headquartered here in Henderson, NV (just outside of Las Vegas), I will be spending much of my time across the border in California, where the impending expansion of a large military base has resulted in the translocation of several hundred tortoises. USGS is responsible not only for relocating these tortoises, but also monitoring a significant portion of them before and after the move. Here are some photos from my first few weeks.




First off, for reference, here is a USGS map showing the extent of the Mojave Desert






And here is the range of the Desert Tortoise






The USGS office in Henderson, NV











On the way to the first field site in Nevada.

























The habitat here is characterized by Creosote bush(Larrea tridentata), White Bursage (Ambrosia dumosa), Mojave Yucca (Yucca schidigera), and Joshua Trees (Yucca brevifolia).






Landscape with Joshua Tree












They can get much bigger than this (up to 15 m) and may live for several hundred years. Joshua Trees are (for the most part) found only in the Mojave Desert and are an important component of the desert ecosystem as they provide shelter, food, and shade for many animals.















Young Joshua Tree from above









Mojave Yucca (Yucca schidigera)












Beavertail Cactus (Optunia basilaris)









Vanessa tracks a tortoise






Burrow entrance






Checking to see this is the right burrow






Making a burrow tag









On the way to another NV study site.






This is the site of a study examining the effects of invasive vegetation and dust suppressants on the physiology of desert tortoises. Each fenced in pen contains several young tortoises.












A sprinkler system provides water to the enclosures






While the Mojave has historically been free of fires, recently the spread of invasive grasses has facilitated fires. At this recently burned site we are studying the effects of fire on desert tortoises.






Burned Joshua Tree












Horse bones












The crew






AJ inserts temperature loggers into a tortoise burrow









Barrel Cactus (Ferocactus cylindraceus)















Hedgehog Cactus (Echinocereus engelmannii)









Silver/Golden Cholla (Cylindropuntia echinocarpa)












Cholla skeleton









Black-tailed Jackrabbit (Lepus californicus)









First herp sighting, a Side-blotched Lizard (Uta stansburiana)






Going for a hike












From up here you can clearly see the border between the burned (lighter) and unburned (darker) areas









Desert Trumpet (Eriogonum inflatum)






We took a trip to the Desert Tortoise Conservation Center (DTCC), which is home to over 1,000 “rescue” tortoises. See the DTCC’s blog here.









Las Vegas skyline in the distance






Adult tortoise pens









Pens housing juvenile tortoises being used for a USGS study






Emma checking out the pens









Baby tortoise out sunning






Another young tortoise in artificial burrow
























Repairing the shade tarp over the pen









Now on to California…






Hiking to one of our many weather stations to download data



















Checking out an old mine









Someone’s shack






Tort-ass (note cobwebs at burrow entrance – this tortoise has not left the burrow anytime recently)






A caliche burrow, for the more upscale tortoise






Tracking






Checking inside a burrow






Marianne and Jose recording data






Jose found a second tortoise in the burrow of the one he had tracked, so he pulled it out to see if we could put a transmitter on it.





They can be hard to reach






Got it! But notice it already has a transmitter – at the time we could not verify the identity of this tortoise, and because there was a possibility its transmitter had died, we attached a temporary one.















Annuli















Patrick tapes on the temporary transmitter












While most tortoises remain inactive during the winter here, there are exceptions. For example, here’s a young tortoise I found in the process of digging a new burrow. Note the portions of the carapace where parts of the keratinized scutes are missing and bone is exposed. Not sure of the cause of this, but it is apparently pretty common. Any thoughts?











Another mine









Oxidized copper









Tortoise plastron bones






Burrow with evidence of predation (tortoise could not be located)






Erodium cicutarium (introduced)











Patrick weighs a new tortoise






Measuring shell dimensions





















You can tell this one is a male by its concave plastron






The shell is cleaned before attaching the transmitter






Attaching the transmitter






Labeling transmitter with the tortoise ID#









Extra reinforcement






Silicone gel is used between the scutes to allow for flexibility with growth






Finally, the tortoise ID# is glued onto the shell.









The finished product










Well that’s all for now, lots more to come once the tortoises start to warm up!

-Zach













Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7

Very cool....keep up the good work

what nhappens when the torts shed those scutes????

Awesome work man! The burrow that may have been dug up by a predator -- is it possible some sort of mammal excavated the burrow for its own use (other than just to get a meal)? In the southeast there are a number of other species that will enlarge tortoise burrows to use as shelters of their own.



Yo Bob, what makes you think tortoises shed their scutes?

Great post man! I'd love to see a post like this but following the Texas Tortoise.

Thanks for the feedback guys - Gyri, the reason we believe that tortoise was predated was because the enlargement of the burrow entrance coincided with the tortoise's disappearance. Bob, as far as I know tortoises don't shed their scutes.

Looks like a super cool project, thanks for taking me along. Keep posting your work especially the tortoises and cacti.

Looks like predator damage but could be necrotizing scute disease. http://www.jwildlifedis.org/cgi/reprint/37/2/223.pdf


While most tortoises remain inactive during the winter here, there are exceptions. For example, here’s a young tortoise I found in the process of digging a new burrow. Note the portions of the carapace where parts of the keratinized scutes are missing and bone is exposed. Not sure of the cause of this, but it is apparently pretty common. Any thoughts?

Hi Zach
I live not far from Henderson & have been documenting herps in the eastern Mojave for sime time. If you're at all interested in info-sharing send me a PM.
Bob