October 7, 2022 • 24 mins
For this episode, Amazing Wildlife is headed towards the Mojave Desert to spotlight a long-lived species known for its thick shell, the desert tortoise! Hosts Rick and Ebone reveal facts about these tortoises, including their surprising speed and why they are classified as a keystone species (meaning if you protect this species you’ll also protect several others). Melissa Merrick, Associate Director of Recovery Ecology, joins the show to discuss how San Diego Zoo Wildlife Alliance and its partners are working to help these tortoises survive after years of population declines.
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Episode Transcript
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Speaker 1 (00:04):
Hi, I'm Ebony Money and I'm Rich Schwartz. Welcome to
Amazing Wildlife, where we explore the unique stories of wildlife
from around the world and uncover fascinating animal facts. This
podcast is a production of My Heart Radio and San
Diego Zoo Wildlife Alliance, in international nonprofit conservation organization behind
the San Diego Zoo and Safari Park. This next animal
(00:27):
is considered a key stone species, meaning if you protect
this species, you'll also protect several others. This animal has
the unique ability to retract its head, legs, and softer
body parts from predators, and it's found in the Mojave Desert.
Today we're learning about the desert tortoise. Rick. As I mentioned,
(00:51):
the desert tortoise is a key stone species. How does
an animal get that title? Well, interestingly enough of an
An animal is considered a keystone species when it's normal
actions and activities within its ecosystem results in supporting the
life of other organisms in the ecosystem. Another way to
look at it is if the keystone species should disappear,
(01:14):
the ecosystem would be dramatically different or cease to even
exist altogether. In the case of the desert tortoise. There
are burrows that they dig are used by many other
species for dens and protection from the ruthless desert weather. Additionally,
they are sea disperses for the few plants in the
desert ecosystem, and they break up the ground that would
otherwise be impenetrable, allowing desert vegetation to take hold. That's fascinating,
(01:39):
So Rick, I think it's safe to say that the
desert tortoise is an essential resident of the Mojave Desert.
Let's talk more about the Mojave Desert region, which is
mostly in California and Nevada, with small parts extending to
Arizona and Utah. What can you tell us about the
wildlife fare, for instance, what other animals call it home.
(02:03):
Oh it's kind of funny, I think when a lot
of us imagine the desert, we think of just a hot, dry,
sandy habitat with little to no life. But if you
should ever be lucky enough to visit the Mojave Desert,
you will be pleasantly surprised at how much life thrives
in the desert. You can see big horn sheep, burrowing owls, roadrunners,
(02:23):
parriss hawks, countless lizards, snakes, jack rabbits, mountain lions, and
so much more, each species finding its own way to
survive and what can be considered a pretty tough climate
to live in. Yeah, speaking of that, deserts are known
for harsh temperatures and for being dry environments. So what
do the desert tortoises eat in this habitat Believe it
(02:47):
or not, ebony. Desert tortoises are very resourceful and can
survive on little to no water. They do rely on
areas with high diversity of plants species though for food.
The diversity of plants allows for some sort of food
to be available most of the year, as different plants
grow in different seasons and when it comes to water well,
for example, of the plants to eat, which can be grasses, shrubs, cacti,
(03:08):
and wildflowers, well, they get much of their needed water
from these food sources. I'm sure that many kids are
familiar with the tortoise and the Hair story, and if not,
it's where the tortoise character slowly and steadily outsmart at
the hair to ultimately beat the hair in a race.
I used to love that story, but it's probably not
(03:31):
a great idea to derive your wildlife knowledge and facts
I've learned from fables. Good point. Just for fun, I've
got to ask, is the tortoise indeed known for its intelligence? Well?
Have any? I think it's fair to say it depends
on how you measure that intelligence. I mean, if you
(03:52):
were to ask a tortoise to complete a math test, well,
it probably won't do so well. But if you observe
the way a tortoise manages to thrive in a desert climate,
I think it would be fair to say they're pretty smart.
Oh and get this. A study was done to see
if tortoises work capable of social learning. They did this
by hiding food in certain areas and having one tortoise
(04:12):
watch as another tortoise found the food. Next, the food
was set up again in the same hidden areas, and
the tortoise that was watching before was able to find
the hidden food directly with no problem. This indicated to
researchers that tortoises are capable of social learning, a trade
thought to have evolved as a special cognitive adaptation in
social animals. Very interesting. So they are pretty intelligent, right,
(04:36):
I would say they're smart enough to do what they
need to do so. Now, that story also touches on
just how slow tortoises are known to be and how
slowly they move. But how slow are they m Ebony,
I think it's a matter of perspective. When moving directly
and with purpose, A desert tortoise moves at about two
to three miles an hour, but they usually moved at
(04:59):
about a isle an hour on a standard pace. Compared
to how we move around, that's pretty slow, especially when
you consider the average humans walking paces around three to
four miles per hour. But compared to us, snail tortoises
are rather quick. Oh and seeing as we're talking about
this because the tortoise and the hair story, jack rabbits
that live in the same region as tortoises can reach
(05:19):
speeds of thirty five to forty miles an hour if needed,
just so you know, making it even more impressive that
the tortoise beat the hair right exactly. Interestingly, from what
I understand, desert tortoises don't actually do a whole lot
of moving around. In fact, I read that they're mostly
(05:39):
inactive for most of the year. What's that about, Well,
it's true, evany, in general, desert tortoises want to conserve
whatever energy they have because resources can be scarce and
the other side of that then, as far as being
inactive for most of the year, will desert tortoises have
the ability to hibernate and do so when all these
resources are really low in the winter months. They will
hibernate October through early March by digging burrows underground and
(06:03):
hibernating there during that time. These burrows can be pretty
deep too. For example, they can extend down about three
to five ft, usually at a forty five degree angle.
They have also been known to create a den or cave,
dug horizontally into the banks of dry river washes and
extending eight to thirty feet. Normally, one burrow houses a
(06:24):
single individual or one male and one female, but one
scientist did record seventeen tortoises using the same winter den.
I want to learn more about the burrows because we've
highlighted a few species that have occupied burrows or created
burrows of their own to house their young, high from predators,
or to keep warm, et cetera. In some cases, these
(06:48):
animals take over the burrows of another animal. Um. How
does the desert tortoise come about getting its burrow well.
The desert tortoise has a body structure really it's perfect
for excavating soil, no matter how dry or densely packed
that soil is. Their front legs are structured like gardening trowels,
with thick, straight claws to help scoop dirt away and
(07:10):
back as they dig. Their back legs are like strong
little pillars that help stabilize the body as the front
limbs are doing all that digging. What they lack in speed,
they make up for an absolute strength and tenacity when
it comes to digging. And going back to the desert
tortoise being a keystone species, their structure and strength allows
them to create burrows in hard desert soils that other
(07:32):
species would not be able to dig into at all. Essentially,
the desert tortoises creating living accommodations for others, not just themselves.
That's great. The desert tortoise is listed as vulnerable unfortunately,
meaning it's at a high risk of unnatural human caused
extinction without further human intervention. So what are some of
(07:55):
these threats? Well, ebony. As we see with many species,
it's not just thing, but a combination of several things
happening at once that's causing challenges for the desert tortoise.
The most obvious human activities that directly impact them are
getting hit by cars when crossing the road, or when
people go off roading through tortoise habitats and they drive
off the groomed trails, they end up collapsing burrows and
(08:16):
causing harm to the tortoises, and sadly, people will use
them as target practice when illegally discharging firearms in the desert.
Climate change has created longer dry seasons as well, so
drought and wildfires are a problem too. These problems, along
with disease from introduced tortoises that were former pets, and
habitat loss due to urban and suburban development, have all
(08:37):
created sort of this perfect storm for a population decline.
And I'm sure our listeners know this by now, but
it bears repeating. With all of these challenges the tortoises
are facing being human created, well, that means we can
also create the solutions to help turn things around for them,
and there are several organizations, including San Diego Zoo Wildlife
Alliance doing some really great work for the desert tortoises.
(09:00):
I love it. How you always find a way to
do a positive spin. The thing is, when we start
to study some of the challenges wildlife faces, it can
feel very overwhelming and so sometimes we just want to
walk away from it. And I think the value and
understanding that people are making a difference will really inspire
others to join us in making some changes for this wildlife. Well,
(09:21):
I'm inspired, So thank you, Rick. What can you tell
us about the desert tortoises social structure if any, Because
this is a reptile rarely seen in nature, but when
it's seen in maybe like nature photography, I see images
of like one tortoise. I can't recall seeing images of
groups of tortoises. Yes, ebony, the desert tortoise is considered
(09:44):
to be a solitary animal. There have been plenty of
observations in the wild of them sharing burrows. However, we
have yet to see or confirm any behavior that would
be considered social. And I purposely say yet, because if
there's anything I have learned from studying animals, just because
we haven't observed it doesn't mean it doesn't happen. That
being said, we do know that when males come across
(10:06):
each other they might fight for dominance, especially during the
breeding season. They will grapple, push and shove an attempt
to flip their opponent over. They use a gol or horn,
appointed extension from the front part of the lower shell
as a device to help flip the other tortoise over.
Males and females both have the gol or horn, but
it's much longer and more pronounced in males, making it
(10:27):
a great tool for their wrestling matches. That brings me
to my next question and the conversation about mating and
possibly the most fascinating fact that I came across when
setting up for this conversation, which is that the female
tortoise can give birth up to fifteen years after mating
(10:49):
with a male. How is this possible? Okay, ebony. This
may sound kind of weird, but it really isn't too
uncommon in the animal kingdom. For many species, like the
desert tortoise, sometimes conditions are not at their best for
creating and laying eggs. For the females to create eggs,
she needs to be in an environment with plenty of
food and all the necessary resources to be in good
(11:11):
health to create and lay her eggs. If her body
is not up to the needed demands of creating and
laying eggs, her body can retain the sperm from the
mail and lay her fertile eggs later up to fifteen
years after mating. Wow. Coming up, we'll talk to Melissa Merrick,
an Associate director of Recovery Ecology with the San Diego
(11:34):
Zoo Wildlife Alliance, about a collaboration project to save the
desert tortoise. But first this now it's time for the
San Diego Zoom Minute, an opportunity for you to learn
what's new at the Zoo. San Diego Zoo Wildlife Alliances
(11:55):
conservation program with the desert tortoise began in two thousand
nine when, at the request of our partners, we took
responsibility for managing the Desert Tortoise Conservation Center near Las Vegas, Nevada.
The center contributed to recovery of the tortoise through collaborative research, conservation, training,
and education. Together, we rescued, cared for, and released more
(12:15):
than two thousand, seven hundred tortoises at six sites. Did
you know if you startle a desert tortoise, it could
void or empty its bladder, leading to dehydration and possibly death.
So you wouldn't want to do that, So be careful
how you interact with wildlife while visiting Mohammi Desert. Today
(12:41):
we're talking about the desert tortoise living in a harsh environment.
The desert tortoise is lucky to get a few drinks
of water a year. What's more, it's threatened by predators,
collisions with vehicles, disease and more. Melissa America is an
Associated director of Recovery Cology with San Diego Zoo Wildlife Alliance.
(13:04):
She's here to tell us about the desert tortoise recovery program.
Him Melissa, Hey embedy, So, what is the goal of
the San Diego Zoo Wildlife Alliances Desert Tortoise Recovery Program.
One of the main goals in the desert tortoise Recovery
program is to understand some of the threats that are
(13:24):
affecting the desert tortoises in the Western Mojave or the
Mojabi Desert in general, and to try to mitigate those threats.
And in order to mitigate those threats, we first have
to understand what these individuals need to survive. And we
are really focusing on the smallest individuals, the hatchlings and
juvenile tortoises, and figuring out ways that we can help
(13:48):
this smallest age class survive into adulthood. And talk to
me more about the research or or the investigation. What
is your work? What are the steps that go into
your work? Right? So that's a great question. And so
the desert tortoise recovery program is really involved in a
two step process. The first step is raising young tortoises
(14:09):
to a little bit older aged so we can release
them at a time when they're less vulnerable to predation,
effectively giving them a head start in life. And so
this is a process that's called head starting. So we're
really trying to figure out some of the best ways
for doing that and how long should we head start individuals.
Can we make head starting more efficient by raising animals
(14:30):
and managed care for a shorter period of time, but
then selecting better release sites that offer more protection from predators.
And so what we're doing right now is we have
adult females that we find on the landscape, and we
attach radio transmitters to these adult females and we actually
(14:50):
monitor them with X rays in the field. And the
one thing that's really cool about X rays is you
can see eggs on them very clearly, and so we
are able to monitor the egg development in these adult females,
and when they get eggs that have a certain shell thickness,
then we bring them into a head Start facility on
Edwards Air Force Space which has adult female size tortoise
(15:13):
burrows all set up, and the adult females are kept
and managed care for a brief period of time for
them to lay their eggs. We continue to monitor those
adult females with regular X rays until we confirm that
they no longer have eggs and they must have laid
their eggs in the burrows at the head start facility.
The adult females are then released back in the wild
(15:34):
exactly where we found them, and then we wait for
the hatchlings to emerge from the burrows, at which point
the hatchlings are raised and managed care for one to
two years. And we've seen with some other animals a
socio dynamic where the mom may protect and care for
the offspring. Is there anything like that that exists in
(15:57):
the world of the desert tortoise. Well, the mothers, once
they lay their eggs, they really don't provide any maternal
care in that sense. But one of the things that
mother tortoises can do to ensure the success of their
clutches and their offspring is to select good sites for
laying eggs, so they can select and manipulate the micro
(16:19):
climate or the temperatures that are within the borough. And
tortoises have temperature dependent sex determination, which means that the
temperature of the borrow influences the sex of the offspring,
and so by selecting different micro climates for her burrows,
she can manipulate the sex ratio of her clutches. And
we're also investigating whether other maternal effects are important, including
(16:44):
the mother's behavior types and whether her offspring inherits of
her behavioral traits. That's fascinating. So desert tortoises are a
keystone species. So as a keystone species, what have been
the impact of the decline in desert tortoise populations in nature? Right?
(17:05):
That's a great question, Ebony. And over the last fifty
or sixty years, there's been a market decline in desert
tortoises on the landscape, and and what's been the most
troubling is we're really not seeing any young tortoises anymore,
which means that the young tortoises are not surviving to adulthood,
and so that's a big concern because once the adult
(17:29):
tortoses that are on the landscape now reach the end
of their natural life, there's really no other tortoises to
replace them, and so that's a big concern. But back
to your keystone species questions, So when you're able to
dig burrows and you're a burrow digger, you're kind of
a big deal. And so in harsh environments like the desert,
these burrows really help many species buffer against extreme temperatures,
(17:51):
including heat and cold. The burrowing process involves lots of
digging and churning up soil, which allows water to reach
the roots of plants and may actually help facilitate the
growth of important shade producing shrubs and wood eat plants
that the tortoises depend on. And these shade producing plants
in turn create cooler and more moist microclimates around them
(18:14):
at their bases that promote the growth of annual flowering
plants and grasses that are the tortoises preferred food. Tortoises
also may serve as seed dispersers so when they eat
fruits and seeds of other plants while they poop those
out and then they're essentially acting as seed dispersal agents
for those key plants. Then that can be important for
(18:35):
other mammalian herbivores and pollinators. So with fewer tortoises on
the landscape, that means there's fewer homes for other animals,
fewer places to shelter and thermoregulate, less soil, aerasian and
nutrient mixing, which supports key shade producing food plants for
the tortoise, and potentially less seed dispersal for those plants,
which may in the future limit their distribution. What disease
(19:00):
is threatened the desert tortoise and do you also find
that these diseases are present and managed care. Yeah, so
there's two main diseases that tend to threaten desert tortoises,
both in the wild and in managed care. And one
is an upper respiratory disease that's caused by a couple
of different things, some bacterial and some fungal infections, and
(19:22):
that can be present in the wild, but it also
can be present in managed care. And so we do
a lot of bio security measures to try to prevent
any spread of disease because of our activities, and that
includes like every tortoise that we handle, we are always
wearing gloves and sanitizing hands and equipment. After each tortoise
(19:43):
is handled, we are regularly monitoring these individuals for signs
of disease, including looking at their nose and their eyes
to look for any signs of running nose and running eyes.
And then when you're moving tortoises, you want to make
sure that you're not mixing to us is from one
area to another area, and if you're going to be
doing anything like that, there usually is a required quarantine period. Well,
(20:08):
it's what would you say is the best part of
your role in in your position? That's my favorite question.
I get to work with amazing people that includes a
fantastic team of scientists, researchers, and research associates on our
team as well as veterinarians, care specialists and curators within
(20:30):
sdc w A that are all dedicated to conserving threatened
species in the Southwest. And it is so much fun
to be a part of a team that cares this
much and actually gets things done and makes things happen
for conservation. I also really love learning, and one of
the things that I love about this position is that
I get to learn something new pretty much every day,
(20:51):
sometimes multiple times a day. I get to learn from experts,
and I include in that category of experts the actual
animals themselves. So I get to learn from tor uses
and they help me understand what they need. We're always
trying to figure out how to ask questions that the
animals can answer. Then they answer that with their behavioral
responses and their physiological responses and lets us know how
(21:13):
well they're doing in terms of health and body condition,
whether they reproduce, how many offsprings survive, and so on.
I find it really humbly to get to observe and
be around these older adult desert tortoise females, and they
have so much more experience in the desert and knowledge
about the desert and what they need to survive than
(21:34):
I do. Many of them have been around at least
twice as long as I have, and there's just so
much to learn and they have so much wisdom that
I just am super honored to learn from them as
much as I can. And is there anything that we
can do? Can people do anything? To help the desert tortoise. Yeah,
(21:54):
some of the ways that you can be mindful of
desert tortoise conservation when you're when you're visiting the desert
is to make sure are they always drive on designated
routes and maintain appropriate speeds because road collisions are a
big source and mortality for these adult desert tortoises. In particular,
one of the reasons is that people are driving too
fast or they're not watching for desert tortoises. Also, when
(22:15):
you park your car in the desert, it's really important
to always check under your vehicle before you move it
because sometimes tortoises are attracted to the shade that's produced
by the vehicle, and you know, if you don't check
under your car and you drive away, you may have
intavert only run over a tortoise that was taking shelter there.
The other ways that we can help conserve desert tortoises
is to be mindful of our practices such as water
(22:39):
use and being more conservative in our water use and
also not providing as many subsidies for predators when we
live in the desert, and then includes making sure that
we don't leave trash out I know it's hard to
close up water sources because everybody likes water in the desert,
but to the extent possible to minimize the amount of
subsidized water that we provide for wildlife in the desert
(23:01):
might have some impact because it's also used by these
these subsidized predators. Some of the other ways that people
can really influence desert tortoise conservations. Every time you visit
the San Diego Zoo, Safari Park and San Diego Zoo,
your visit is contributing to desert tortoise conservations. So just
by enjoying yourself and supporting the organization in those ways,
(23:22):
you're supporting desert tortoise conservation too. Thank you so much.
We've been talking to Melissa Merrick, and Associate director of
Recovery Ecology with the San Diego Zoo Wildlife Alliances Desert
Tortoise Recovery Program. Great talking with you. Wonderful to talk
to you, Ebany, Thanks for listening. We hope you've enjoyed
learning about the desert tortoise and be sure to subscribe
(23:45):
and tune into next week's episode, in which we bring
you the story of an amphibian with ties to the
Jurassic period and is considered a giant of its kind.
I'm Abny Money and I'm Rich Schwartz. Thanks for listening.
If you would like to find out more about San
Diego Zoo while lack alliance, please visit sdz W a
(24:07):
dot org. Amazing Wildlife is a production of I Heart Radio.
Our producer is Nikkia Swinton and our executive producer is
Marcia to Peina. Our audio engineer and editor is Sierra Spreen.
For more shows from my heart Radio, check out the
I Heart Radio app, Apple podcast, or wherever you listen
to your favorite shows.
Hi, I'm Ebony Money and I'm Rich Schwartz. Welcome to
Amazing Wildlife, where we explore the unique stories of wildlife
from around the world and uncover fascinating animal facts. This
podcast is a production of My Heart Radio and San
Diego Zoo Wildlife Alliance, in international nonprofit conservation organization behind
the San Diego Zoo and Safari Park. This next animal
(00:27):
is considered a key stone species, meaning if you protect
this species, you'll also protect several others. This animal has
the unique ability to retract its head, legs, and softer
body parts from predators, and it's found in the Mojave Desert.
Today we're learning about the desert tortoise. Rick. As I mentioned,
(00:51):
the desert tortoise is a key stone species. How does
an animal get that title? Well, interestingly enough of an
An animal is considered a keystone species when it's normal
actions and activities within its ecosystem results in supporting the
life of other organisms in the ecosystem. Another way to
look at it is if the keystone species should disappear,
(01:14):
the ecosystem would be dramatically different or cease to even
exist altogether. In the case of the desert tortoise. There
are burrows that they dig are used by many other
species for dens and protection from the ruthless desert weather. Additionally,
they are sea disperses for the few plants in the
desert ecosystem, and they break up the ground that would
otherwise be impenetrable, allowing desert vegetation to take hold. That's fascinating,
(01:39):
So Rick, I think it's safe to say that the
desert tortoise is an essential resident of the Mojave Desert.
Let's talk more about the Mojave Desert region, which is
mostly in California and Nevada, with small parts extending to
Arizona and Utah. What can you tell us about the
wildlife fare, for instance, what other animals call it home.
(02:03):
Oh it's kind of funny, I think when a lot
of us imagine the desert, we think of just a hot, dry,
sandy habitat with little to no life. But if you
should ever be lucky enough to visit the Mojave Desert,
you will be pleasantly surprised at how much life thrives
in the desert. You can see big horn sheep, burrowing owls, roadrunners,
(02:23):
parriss hawks, countless lizards, snakes, jack rabbits, mountain lions, and
so much more, each species finding its own way to
survive and what can be considered a pretty tough climate
to live in. Yeah, speaking of that, deserts are known
for harsh temperatures and for being dry environments. So what
do the desert tortoises eat in this habitat Believe it
(02:47):
or not, ebony. Desert tortoises are very resourceful and can
survive on little to no water. They do rely on
areas with high diversity of plants species though for food.
The diversity of plants allows for some sort of food
to be available most of the year, as different plants
grow in different seasons and when it comes to water well,
for example, of the plants to eat, which can be grasses, shrubs, cacti,
(03:08):
and wildflowers, well, they get much of their needed water
from these food sources. I'm sure that many kids are
familiar with the tortoise and the Hair story, and if not,
it's where the tortoise character slowly and steadily outsmart at
the hair to ultimately beat the hair in a race.
I used to love that story, but it's probably not
(03:31):
a great idea to derive your wildlife knowledge and facts
I've learned from fables. Good point. Just for fun, I've
got to ask, is the tortoise indeed known for its intelligence? Well?
Have any? I think it's fair to say it depends
on how you measure that intelligence. I mean, if you
(03:52):
were to ask a tortoise to complete a math test, well,
it probably won't do so well. But if you observe
the way a tortoise manages to thrive in a desert climate,
I think it would be fair to say they're pretty smart.
Oh and get this. A study was done to see
if tortoises work capable of social learning. They did this
by hiding food in certain areas and having one tortoise
(04:12):
watch as another tortoise found the food. Next, the food
was set up again in the same hidden areas, and
the tortoise that was watching before was able to find
the hidden food directly with no problem. This indicated to
researchers that tortoises are capable of social learning, a trade
thought to have evolved as a special cognitive adaptation in
social animals. Very interesting. So they are pretty intelligent, right,
(04:36):
I would say they're smart enough to do what they
need to do so. Now, that story also touches on
just how slow tortoises are known to be and how
slowly they move. But how slow are they m Ebony,
I think it's a matter of perspective. When moving directly
and with purpose, A desert tortoise moves at about two
to three miles an hour, but they usually moved at
(04:59):
about a isle an hour on a standard pace. Compared
to how we move around, that's pretty slow, especially when
you consider the average humans walking paces around three to
four miles per hour. But compared to us, snail tortoises
are rather quick. Oh and seeing as we're talking about
this because the tortoise and the hair story, jack rabbits
that live in the same region as tortoises can reach
(05:19):
speeds of thirty five to forty miles an hour if needed,
just so you know, making it even more impressive that
the tortoise beat the hair right exactly. Interestingly, from what
I understand, desert tortoises don't actually do a whole lot
of moving around. In fact, I read that they're mostly
(05:39):
inactive for most of the year. What's that about, Well,
it's true, evany, in general, desert tortoises want to conserve
whatever energy they have because resources can be scarce and
the other side of that then, as far as being
inactive for most of the year, will desert tortoises have
the ability to hibernate and do so when all these
resources are really low in the winter months. They will
hibernate October through early March by digging burrows underground and
(06:03):
hibernating there during that time. These burrows can be pretty
deep too. For example, they can extend down about three
to five ft, usually at a forty five degree angle.
They have also been known to create a den or cave,
dug horizontally into the banks of dry river washes and
extending eight to thirty feet. Normally, one burrow houses a
(06:24):
single individual or one male and one female, but one
scientist did record seventeen tortoises using the same winter den.
I want to learn more about the burrows because we've
highlighted a few species that have occupied burrows or created
burrows of their own to house their young, high from predators,
or to keep warm, et cetera. In some cases, these
(06:48):
animals take over the burrows of another animal. Um. How
does the desert tortoise come about getting its burrow well.
The desert tortoise has a body structure really it's perfect
for excavating soil, no matter how dry or densely packed
that soil is. Their front legs are structured like gardening trowels,
with thick, straight claws to help scoop dirt away and
(07:10):
back as they dig. Their back legs are like strong
little pillars that help stabilize the body as the front
limbs are doing all that digging. What they lack in speed,
they make up for an absolute strength and tenacity when
it comes to digging. And going back to the desert
tortoise being a keystone species, their structure and strength allows
them to create burrows in hard desert soils that other
(07:32):
species would not be able to dig into at all. Essentially,
the desert tortoises creating living accommodations for others, not just themselves.
That's great. The desert tortoise is listed as vulnerable unfortunately,
meaning it's at a high risk of unnatural human caused
extinction without further human intervention. So what are some of
(07:55):
these threats? Well, ebony. As we see with many species,
it's not just thing, but a combination of several things
happening at once that's causing challenges for the desert tortoise.
The most obvious human activities that directly impact them are
getting hit by cars when crossing the road, or when
people go off roading through tortoise habitats and they drive
off the groomed trails, they end up collapsing burrows and
(08:16):
causing harm to the tortoises, and sadly, people will use
them as target practice when illegally discharging firearms in the desert.
Climate change has created longer dry seasons as well, so
drought and wildfires are a problem too. These problems, along
with disease from introduced tortoises that were former pets, and
habitat loss due to urban and suburban development, have all
(08:37):
created sort of this perfect storm for a population decline.
And I'm sure our listeners know this by now, but
it bears repeating. With all of these challenges the tortoises
are facing being human created, well, that means we can
also create the solutions to help turn things around for them,
and there are several organizations, including San Diego Zoo Wildlife
Alliance doing some really great work for the desert tortoises.
(09:00):
I love it. How you always find a way to
do a positive spin. The thing is, when we start
to study some of the challenges wildlife faces, it can
feel very overwhelming and so sometimes we just want to
walk away from it. And I think the value and
understanding that people are making a difference will really inspire
others to join us in making some changes for this wildlife. Well,
(09:21):
I'm inspired, So thank you, Rick. What can you tell
us about the desert tortoises social structure if any, Because
this is a reptile rarely seen in nature, but when
it's seen in maybe like nature photography, I see images
of like one tortoise. I can't recall seeing images of
groups of tortoises. Yes, ebony, the desert tortoise is considered
(09:44):
to be a solitary animal. There have been plenty of
observations in the wild of them sharing burrows. However, we
have yet to see or confirm any behavior that would
be considered social. And I purposely say yet, because if
there's anything I have learned from studying animals, just because
we haven't observed it doesn't mean it doesn't happen. That
being said, we do know that when males come across
(10:06):
each other they might fight for dominance, especially during the
breeding season. They will grapple, push and shove an attempt
to flip their opponent over. They use a gol or horn,
appointed extension from the front part of the lower shell
as a device to help flip the other tortoise over.
Males and females both have the gol or horn, but
it's much longer and more pronounced in males, making it
(10:27):
a great tool for their wrestling matches. That brings me
to my next question and the conversation about mating and
possibly the most fascinating fact that I came across when
setting up for this conversation, which is that the female
tortoise can give birth up to fifteen years after mating
(10:49):
with a male. How is this possible? Okay, ebony. This
may sound kind of weird, but it really isn't too
uncommon in the animal kingdom. For many species, like the
desert tortoise, sometimes conditions are not at their best for
creating and laying eggs. For the females to create eggs,
she needs to be in an environment with plenty of
food and all the necessary resources to be in good
(11:11):
health to create and lay her eggs. If her body
is not up to the needed demands of creating and
laying eggs, her body can retain the sperm from the
mail and lay her fertile eggs later up to fifteen
years after mating. Wow. Coming up, we'll talk to Melissa Merrick,
an Associate director of Recovery Ecology with the San Diego
(11:34):
Zoo Wildlife Alliance, about a collaboration project to save the
desert tortoise. But first this now it's time for the
San Diego Zoom Minute, an opportunity for you to learn
what's new at the Zoo. San Diego Zoo Wildlife Alliances
(11:55):
conservation program with the desert tortoise began in two thousand
nine when, at the request of our partners, we took
responsibility for managing the Desert Tortoise Conservation Center near Las Vegas, Nevada.
The center contributed to recovery of the tortoise through collaborative research, conservation, training,
and education. Together, we rescued, cared for, and released more
(12:15):
than two thousand, seven hundred tortoises at six sites. Did
you know if you startle a desert tortoise, it could
void or empty its bladder, leading to dehydration and possibly death.
So you wouldn't want to do that, So be careful
how you interact with wildlife while visiting Mohammi Desert. Today
(12:41):
we're talking about the desert tortoise living in a harsh environment.
The desert tortoise is lucky to get a few drinks
of water a year. What's more, it's threatened by predators,
collisions with vehicles, disease and more. Melissa America is an
Associated director of Recovery Cology with San Diego Zoo Wildlife Alliance.
(13:04):
She's here to tell us about the desert tortoise recovery program.
Him Melissa, Hey embedy, So, what is the goal of
the San Diego Zoo Wildlife Alliances Desert Tortoise Recovery Program.
One of the main goals in the desert tortoise Recovery
program is to understand some of the threats that are
(13:24):
affecting the desert tortoises in the Western Mojave or the
Mojabi Desert in general, and to try to mitigate those threats.
And in order to mitigate those threats, we first have
to understand what these individuals need to survive. And we
are really focusing on the smallest individuals, the hatchlings and
juvenile tortoises, and figuring out ways that we can help
(13:48):
this smallest age class survive into adulthood. And talk to
me more about the research or or the investigation. What
is your work? What are the steps that go into
your work? Right? So that's a great question. And so
the desert tortoise recovery program is really involved in a
two step process. The first step is raising young tortoises
(14:09):
to a little bit older aged so we can release
them at a time when they're less vulnerable to predation,
effectively giving them a head start in life. And so
this is a process that's called head starting. So we're
really trying to figure out some of the best ways
for doing that and how long should we head start individuals.
Can we make head starting more efficient by raising animals
(14:30):
and managed care for a shorter period of time, but
then selecting better release sites that offer more protection from predators.
And so what we're doing right now is we have
adult females that we find on the landscape, and we
attach radio transmitters to these adult females and we actually
(14:50):
monitor them with X rays in the field. And the
one thing that's really cool about X rays is you
can see eggs on them very clearly, and so we
are able to monitor the egg development in these adult females,
and when they get eggs that have a certain shell thickness,
then we bring them into a head Start facility on
Edwards Air Force Space which has adult female size tortoise
(15:13):
burrows all set up, and the adult females are kept
and managed care for a brief period of time for
them to lay their eggs. We continue to monitor those
adult females with regular X rays until we confirm that
they no longer have eggs and they must have laid
their eggs in the burrows at the head start facility.
The adult females are then released back in the wild
(15:34):
exactly where we found them, and then we wait for
the hatchlings to emerge from the burrows, at which point
the hatchlings are raised and managed care for one to
two years. And we've seen with some other animals a
socio dynamic where the mom may protect and care for
the offspring. Is there anything like that that exists in
(15:57):
the world of the desert tortoise. Well, the mothers, once
they lay their eggs, they really don't provide any maternal
care in that sense. But one of the things that
mother tortoises can do to ensure the success of their
clutches and their offspring is to select good sites for
laying eggs, so they can select and manipulate the micro
(16:19):
climate or the temperatures that are within the borough. And
tortoises have temperature dependent sex determination, which means that the
temperature of the borrow influences the sex of the offspring,
and so by selecting different micro climates for her burrows,
she can manipulate the sex ratio of her clutches. And
we're also investigating whether other maternal effects are important, including
(16:44):
the mother's behavior types and whether her offspring inherits of
her behavioral traits. That's fascinating. So desert tortoises are a
keystone species. So as a keystone species, what have been
the impact of the decline in desert tortoise populations in nature? Right?
(17:05):
That's a great question, Ebony. And over the last fifty
or sixty years, there's been a market decline in desert
tortoises on the landscape, and and what's been the most
troubling is we're really not seeing any young tortoises anymore,
which means that the young tortoises are not surviving to adulthood,
and so that's a big concern because once the adult
(17:29):
tortoses that are on the landscape now reach the end
of their natural life, there's really no other tortoises to
replace them, and so that's a big concern. But back
to your keystone species questions, So when you're able to
dig burrows and you're a burrow digger, you're kind of
a big deal. And so in harsh environments like the desert,
these burrows really help many species buffer against extreme temperatures,
(17:51):
including heat and cold. The burrowing process involves lots of
digging and churning up soil, which allows water to reach
the roots of plants and may actually help facilitate the
growth of important shade producing shrubs and wood eat plants
that the tortoises depend on. And these shade producing plants
in turn create cooler and more moist microclimates around them
(18:14):
at their bases that promote the growth of annual flowering
plants and grasses that are the tortoises preferred food. Tortoises
also may serve as seed dispersers so when they eat
fruits and seeds of other plants while they poop those
out and then they're essentially acting as seed dispersal agents
for those key plants. Then that can be important for
(18:35):
other mammalian herbivores and pollinators. So with fewer tortoises on
the landscape, that means there's fewer homes for other animals,
fewer places to shelter and thermoregulate, less soil, aerasian and
nutrient mixing, which supports key shade producing food plants for
the tortoise, and potentially less seed dispersal for those plants,
which may in the future limit their distribution. What disease
(19:00):
is threatened the desert tortoise and do you also find
that these diseases are present and managed care. Yeah, so
there's two main diseases that tend to threaten desert tortoises,
both in the wild and in managed care. And one
is an upper respiratory disease that's caused by a couple
of different things, some bacterial and some fungal infections, and
(19:22):
that can be present in the wild, but it also
can be present in managed care. And so we do
a lot of bio security measures to try to prevent
any spread of disease because of our activities, and that
includes like every tortoise that we handle, we are always
wearing gloves and sanitizing hands and equipment. After each tortoise
(19:43):
is handled, we are regularly monitoring these individuals for signs
of disease, including looking at their nose and their eyes
to look for any signs of running nose and running eyes.
And then when you're moving tortoises, you want to make
sure that you're not mixing to us is from one
area to another area, and if you're going to be
doing anything like that, there usually is a required quarantine period. Well,
(20:08):
it's what would you say is the best part of
your role in in your position? That's my favorite question.
I get to work with amazing people that includes a
fantastic team of scientists, researchers, and research associates on our
team as well as veterinarians, care specialists and curators within
(20:30):
sdc w A that are all dedicated to conserving threatened
species in the Southwest. And it is so much fun
to be a part of a team that cares this
much and actually gets things done and makes things happen
for conservation. I also really love learning, and one of
the things that I love about this position is that
I get to learn something new pretty much every day,
(20:51):
sometimes multiple times a day. I get to learn from experts,
and I include in that category of experts the actual
animals themselves. So I get to learn from tor uses
and they help me understand what they need. We're always
trying to figure out how to ask questions that the
animals can answer. Then they answer that with their behavioral
responses and their physiological responses and lets us know how
(21:13):
well they're doing in terms of health and body condition,
whether they reproduce, how many offsprings survive, and so on.
I find it really humbly to get to observe and
be around these older adult desert tortoise females, and they
have so much more experience in the desert and knowledge
about the desert and what they need to survive than
(21:34):
I do. Many of them have been around at least
twice as long as I have, and there's just so
much to learn and they have so much wisdom that
I just am super honored to learn from them as
much as I can. And is there anything that we
can do? Can people do anything? To help the desert tortoise. Yeah,
(21:54):
some of the ways that you can be mindful of
desert tortoise conservation when you're when you're visiting the desert
is to make sure are they always drive on designated
routes and maintain appropriate speeds because road collisions are a
big source and mortality for these adult desert tortoises. In particular,
one of the reasons is that people are driving too
fast or they're not watching for desert tortoises. Also, when
(22:15):
you park your car in the desert, it's really important
to always check under your vehicle before you move it
because sometimes tortoises are attracted to the shade that's produced
by the vehicle, and you know, if you don't check
under your car and you drive away, you may have
intavert only run over a tortoise that was taking shelter there.
The other ways that we can help conserve desert tortoises
is to be mindful of our practices such as water
(22:39):
use and being more conservative in our water use and
also not providing as many subsidies for predators when we
live in the desert, and then includes making sure that
we don't leave trash out I know it's hard to
close up water sources because everybody likes water in the desert,
but to the extent possible to minimize the amount of
subsidized water that we provide for wildlife in the desert
(23:01):
might have some impact because it's also used by these
these subsidized predators. Some of the other ways that people
can really influence desert tortoise conservations. Every time you visit
the San Diego Zoo, Safari Park and San Diego Zoo,
your visit is contributing to desert tortoise conservations. So just
by enjoying yourself and supporting the organization in those ways,
(23:22):
you're supporting desert tortoise conservation too. Thank you so much.
We've been talking to Melissa Merrick, and Associate director of
Recovery Ecology with the San Diego Zoo Wildlife Alliances Desert
Tortoise Recovery Program. Great talking with you. Wonderful to talk
to you, Ebany, Thanks for listening. We hope you've enjoyed
learning about the desert tortoise and be sure to subscribe
(23:45):
and tune into next week's episode, in which we bring
you the story of an amphibian with ties to the
Jurassic period and is considered a giant of its kind.
I'm Abny Money and I'm Rich Schwartz. Thanks for listening.
If you would like to find out more about San
Diego Zoo while lack alliance, please visit sdz W a
(24:07):
dot org. Amazing Wildlife is a production of I Heart Radio.
Our producer is Nikkia Swinton and our executive producer is
Marcia to Peina. Our audio engineer and editor is Sierra Spreen.
For more shows from my heart Radio, check out the
I Heart Radio app, Apple podcast, or wherever you listen
to your favorite shows.
Hosts And Creators
Rick Schwartz
Marco Wendt
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