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The desert tortoise without the hare

Updated Monday, 9th May 2011

How important are desert tortoises to the desert ecosystem? The Saving Species team talks to biologist Kimberley Field in this extended interview

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Copyright The Open University


Interviewer:  Well we've finally arrived at our first release location.  We've driven about an hour south of Las Vegas into the desert plains and I'm with Kimberly Field from the US Fish & Wildlife Service, who is a Desert Tortoise Recovery Biologist.  What's the next step?  We have, wonderful, we have six tortoises in crates, what's going on here?

Kimberley:  Well they're almost ready to be released but we're giving them one last soak, an opportunity for hydration before we release them.

Interviewer:  They're surprisingly big aren’t they?  Can I actually get down here and touch this fella?  He's in a crate but he is slate grey and so not much colour to him, what is he about, he's about a foot and a half in length and?

Kimberley:  Yeah, and he's quite heavy.  What we're going to do is weigh him and then let him sit in some water, and he'll either drink or they actually absorb water through their cloacae as well and store that in their bladder, and then we'll weigh him again to see how much water he in-took and then he'll be set for release.

Interviewer:  And he's also [got] transmitters attached to him, sort of welded to him really.

Kimberley:  Yeah, they're radio transmitter epoxied on, and then we also have a GPS logger attached, so we can get more precise fine scale movements on where he goes after we release him.

Interviewer:  Now what's the reason for weighing them and actually giving them a soaking before you release them?

Kimberley:  Once they're out here the next rain is pretty unpredictable, and so although they've been in captivity and have had good food and water, it's just kind of one last chance to hydrate before they're on their own.

Interviewer:  But I did read that they can actually survive a year without water can't they?

Kimberley:  They can, but fresh water is very important.  So in order to be able to keep feeding they do need fresh water so that kind of once-a-year drink at minimum is really critical for them.  They don't do well in drought years actually even though they're a desert animal.

Interviewer:  He's peering at us.  He's extended his neck way out of his shell.  He's wondering what the heck is going on and he's sort of nodding at us at the moment.  And they have these wonderful long forelegs as well don't they, very scaled with sharp claws, how does that help them?

Kimberley:  Well, for digging.  So once they're out here they're going to have to dig their own burrows, and they're very good diggers, and so with those forelimbs they're able to really move the soil and the rocks, you'll see how rocky it really is out here, and they're able to dig right through that.

Interviewer:  Well what's interesting also is that it is extremely rocky.  There are lots of these small boulders around and you see straight away how the camouflage will help them because any of these boulders, I mean millions and millions of them around us, could be tortoises couldn’t they?

Kimberley:  Yeah, to the untrained eye, yeah, hard to find the tortoises out here.

Interviewer:  It's quite extraordinary.  All right well I'll let you get on with weighing and soaking him.

Kimberley:  Okay.  So I'm going to put this string down on the ground to lift the tortoise with, wow he's a heavy guy for sure.

Interviewer:  The transmitters that are on him are quite big actually, how will that affect him?

Kimberley:  We do make sure that the transmitters are only a certain percentage of the mass of the tortoise.  So actually to him it's minuscule.  We also try to attach them so that they're not right on top where it might interfere with getting in and out of burrows and caves.  So this does stick up a little bit but the way the burrows are structured it should be okay.

Interviewer:  You just heard the sound of him being doused in some water, and they're going to sit here for sort of 20 minutes or so, is that right, to absorb water?

Kimberley:  Correct, yeah give them a chance to absorb some water.

Interviewer:  We are in this amazing landscape where, as I said, in the desert plains well south of Las Vegas ringed by rocky brown barren hills and mountains, and yet the plain itself is quite green at the moment, it being spring of course.  Now everybody knows that tortoises only eat dandelion leaves and lettuce leaves, and looking around here Kim I can't see a lot of either, so how do they survive out here?  How have they fitted and adapted to this habitat?

Kimberley:  If you notice this little plant right here, that actually is pretty widespread when you look, it's a plantago, they really like to eat that too.

Interviewer:  Tiny little stems.

Kimberley:  So those tiny little ones, yeah, and a lot of the plants that they like to eat are also found in the washes so there’ll be more flowers and things in the areas that are more damp.  But they do well.  Surprisingly, this is actually a pretty good year, and there's lots of this little plantago and some other favourite food items out here.

Interviewer:  It is green but of course it doesn't last long does it?

Kimberley:  No.

Interviewer:  We are out in the desert, so what do they do for the rest of the year?

Kimberley:  They will eat dried grasses and things too.  As long as they have enough water they can dilute their solute levels from the food they're in-taking and they can feed off of the dried material for a long time.  And in July, in a good year, we will get some rains again and hopefully things will green up once more and they can have another chance to get some green stuff.

Interviewer:  Now apart from looking like the rocks and boulders around us what do the tortoises actually contribute to the habitat?  Where do they fit in?

Kimberley:  Well they are really one of the only grazing animals out here in the desert.  So as far as playing that role in the system, spreading seeds of the desert plants that's actually pretty important.  They also provide, through digging burrows, they provide shelter and structure for a lot of other animals in the desert.  There's a number of animals that share burrows with tortoises, even things like burrowing owls and tortoises can sometimes be found together.

Interviewer:  They are the biggest reptile aren’t they in the desert?

Kimberley:  They are.

Interviewer:  The Mojave desert tortoise.

Kimberley:  Right.

Interviewer:  And they also live to extraordinary ages.

Kimberley:  Yeah, they can live in the wild, you know, there are so many threats and predators and things, but they could live 60/70 years probably if they're in a good spot.

Interviewer:  And how old are the ones you’re releasing today?

Kimberley:  Well I would guess, these are all pretty large so they're probably at least, I think they're probably all more than 30 years old.  Some of these guys might be closer to 40ish, hard to say for sure but…

Interviewer:  Wow.

Kimberley:  And some of these I think did come from a captive environment originally and they can grow a little faster when they have a lot of food and water compared to how quickly they'd grow out here naturally.

Interviewer:  Well I think I must have walked pretty much half way across the Mojave Desert to catch up with Paula Khan who is the Conservation Programme Manager and releasing another tortoise underneath a yucca tree and what have we got there, [a] male?

Paula:  That I believe I'll have to check for you, let’s take a quick look, that is a female, yes.

Interviewer:  And she's not moving much yet.

Paula:  No.

Interviewer:  Now why do you believe that translocation is such an important part of trying to restore the numbers of desert tortoise in the Mojave?

Paula:  Well desert tortoises take a very long time to maturity, it can take them 13 to 20 years to reach sexual maturity, so if we just wait for them to make more tortoises to increase the population we could be waiting 25 years, 50 years.  So we want to do everything we can to increase the populations now, and so by releasing healthy adult tortoises into the population we're able to increase those numbers right away and increase the likelihood for success, both in making new tortoises and in their livelihood.

Interviewer:  But why try to preserve this species in particular?  What's so important about this and especially in an era where conservation is moving more towards habitat conservation rather than single species, why this tortoise and why now?

Paula:  Well the desert tortoise is considered a keystone species and that means that it is very very important to the environment and more so than many of the other species that live here and the reason for that is that tortoises dig these great burrows that other animals are able to use, and without those burrows, and therefore without the tortoises, these animals also may not survive and so they're very important in terms of that as well as the fact that they disperse seeds.  So they re-vegetate the desert for all the other animals as well and so they are an icon of the Mojave Desert and everyone often thinks of desert tortoises when they think of the Mojave Desert but their role here as a keystone species and an ecosystem engineer in digging this burrows is just incredibly important.

Interviewer:  Now there have been other translocation projects which haven't worked out too well, I'm thinking about Fort Irwin in California where a lot of the tortoises died out, so what makes you hopeful that this will be different?

Paula:  Well the numbers of tortoises that we're releasing here are much smaller so we can keep a very very close eye on them.  We have people that are going to be out tracking these tortoises every day for the first two weeks that they're out and that's very important so we can check on them, we know if something is wrong and we're able to pull the tortoises back in if we need to.  Because the tortoises came from the Desert Tortoise Conservation Centre we actually have a place to bring them back to, whereas with other translocations they're moving them out of harm’s way so there may not be a place to bring them back to.

Interviewer:  Now you mentioned it earlier, one of the big challenges you have is knowing whether this approach is going to be successful because of the longevity of the tortoise itself and the fact that its reproduction cycle is so long, so when will you be able to see some tangible results in a project which is expensive, we're talking like millions of dollars really here.

Paula:  You're right and it is very important for us to figure out if this is successful so we have markers to judge that but with tortoises you're right, it's going to take years.  If we just follow tortoises for a season or a year or two years that is just a snapshot in the life of a tortoise, and we genuinely want to know in the long-term are we doing the right thing.  So our study is a minimum of five years, we're going to be following them for that amount of time, and they also have other equipment attached to them.  So they don't just have these VHF transmitters where we can go out and look at them once a day, they have GPS data loggers, and these data loggers are going to give us micro information.

So every 30 minutes we're going to know where these tortoises are and that will really help us to understand what kind of habitat they're using and what kinds of movements they're making, which burrows they're in and things like that and we're going to compare them to residents that are actually living here.  So we have a comparison, we know and we have a gauge of what's normal for this habitat so we can see when our tortoises are settled in and we'll do that over a long long period of time.

Interviewer:  Haven't you almost left it too late, I mean numbers did dwindle alarmingly, especially since the 1950s, is it too little too late do you think?

Paula:  I don't know that it's too little too late and the reason that we feel hopeful is that at the Desert Tortoise Conservation Centre we get in about 1,000 desert tortoises a year and these are unwanted pet tortoises, lost tortoises that people have found, so this is an incredible resource for us.  We're getting 1,000 tortoises a year that could potentially be put back out in the desert through this type of research to learn from them.

Interviewer:  See that's one of the things that surprises me actually because you do get people’s pets turning up at the centre, surely those aren’t the right sort of animals to be rereleasing into the wild, especially anything that's been in captivity for too long.

Paula:  Well that's why we do full health assessments on these tortoises.  we look at them, we do observations on them, we do blood work, nasal lavage, oral swabs, so we test their health in many many different ways and they have to stay in quarantine, our entire site is considered a quarantine and in that way we're able to really keep an eye on these tortoises and test them repeatedly and no animal comes to our facility gets looked at and put out for translocation.  So no tortoise has left our facility without having been there for at least a year so we can see them for a full year cycle of their life, make sure that they’re behaviourally and physiologically ready to be placed back out in the desert.

Interviewer:  Will this conservation effort finally take the tortoises off the threatened list, on the endangered species list and if so when?

Paula:  You know that is a really really tough question to answer and, you know, I think that this is just the beginning of us being able to figure that out.  So I can't say for sure, I'm hopeful and I would love to see that happen, but honestly we can't say right now we're so early in our research, but I'm very very hopeful that this is going to be a significant step toward that.

Desert tortoise Copyrighted  image Icon Copyright: BBC [Photographer: Howard Stableford]




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