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A third of the land
on our planet is desert.
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00:00:55,806 --> 00:00:58,893
These great scars
on the face of the Earth ...
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00:00:59,018 --> 00:01:00,811
appear to be lifeless,
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00:01:00,936 --> 00:01:04,064
but surprisingly none are.
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00:01:10,615 --> 00:01:13,784
In all of them,
life manages somehow ...
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00:01:13,868 --> 00:01:16,623
to keep a precarious hold.
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00:01:37,648 --> 00:01:40,192
Not all deserts are hot.
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00:01:40,609 --> 00:01:42,154
Fifty-mile-an-hour winds ...
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00:01:42,249 --> 00:01:44,196
blowing in from Siberia ...
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00:01:44,321 --> 00:01:48,369
bring snow to the Gobi Desert
in Mongolia.
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00:02:14,232 --> 00:02:17,779
From a summer high
of 50 degrees centigrade,
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00:02:17,904 --> 00:02:21,992
the temperature in midwinter
can drop to -40,
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00:02:22,117 --> 00:02:26,206
making this one
of the harshest deserts of all.
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00:02:35,176 --> 00:02:40,264
Few animals can survive
these extreme changes.
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00:02:46,647 --> 00:02:49,108
Wild Bactrian camels —
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00:02:49,233 --> 00:02:51,861
one of the rarest mammals
on the planet.
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00:02:51,986 --> 00:02:54,697
And perhaps the hardiest.
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00:02:55,909 --> 00:02:58,453
Their biggest problem
is the lack of water,
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00:02:58,578 --> 00:03:00,288
particularly now in winter,
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00:03:00,413 --> 00:03:03,833
when the little there is,
is locked up as ice.
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00:03:10,884 --> 00:03:15,057
Surprisingly, snow here never melts.
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00:03:15,265 --> 00:03:20,062
The air is just too cold
and too dry for it to do so.
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00:03:25,236 --> 00:03:28,989
The sun's rays turn it
straight into vapour.
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00:03:29,073 --> 00:03:31,116
It evaporates.
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00:03:39,126 --> 00:03:42,255
But it is the only source
of water,
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00:03:42,338 --> 00:03:45,385
so Bactrian camels eat it.
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00:03:46,261 --> 00:03:47,720
Elsewhere in the world,
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00:03:47,845 --> 00:03:54,435
a camel at a waterhole can drink as much
as 200 litres during a single visit.
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00:03:56,398 --> 00:03:59,901
Here, the strategy is
to take little and often.
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00:04:00,026 --> 00:04:01,444
And with good reason,
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00:04:01,570 --> 00:04:05,325
for filling the stomach
with snow could be fatal.
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00:04:10,873 --> 00:04:12,916
The camels must limit themselves ...
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00:04:13,041 --> 00:04:17,006
to the equivalent
of just 10 litres a day.
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00:04:33,608 --> 00:04:36,529
Winter is the time for breeding.
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00:04:41,159 --> 00:04:45,582
This extraordinary performance
is a male Bactrian camel's way ...
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00:04:45,707 --> 00:04:49,169
of attracting the attention
of a passing female.
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00:04:51,254 --> 00:04:55,761
In summer, the camels can't stray
far from waterholes.
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00:04:56,053 --> 00:04:59,598
But now, with mouthfuls
of snow lying everywhere,
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00:04:59,681 --> 00:05:03,101
they can travel widely
in search of mates.
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00:05:07,191 --> 00:05:13,405
Today, less than a 1,000 of these
desert specialists remain in the wild.
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00:05:13,530 --> 00:05:19,038
The Gobi, hostile though it is,
is their last stronghold.
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00:05:25,338 --> 00:05:28,675
There's no other desert
quite like the Gobi,
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00:05:28,800 --> 00:05:31,928
but why is this place a desert?
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00:05:33,221 --> 00:05:36,476
There is one simple
and massive cause —
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00:05:36,601 --> 00:05:38,103
the Himalayas.
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00:05:42,691 --> 00:05:46,822
Clouds blowing from the south
hit this gigantic barrier.
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00:05:46,947 --> 00:05:48,365
As they're forced upwards,
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00:05:48,490 --> 00:05:51,910
so they empty their moisture
on the mountain slopes,
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00:05:51,994 --> 00:05:55,833
leaving little for the land
on the other side.
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00:06:00,379 --> 00:06:04,717
From the space,
deserts are very conspicuous.
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00:06:07,096 --> 00:06:12,059
Dunes of sand, hundreds of miles long,
streak their surface.
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00:06:16,858 --> 00:06:20,028
With no cloak of vegetation
to conceal them,
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00:06:20,153 --> 00:06:24,824
strange formations are exposed
in the naked rock.
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00:06:30,498 --> 00:06:34,419
Africa's Sahara is
the largest desert of all.
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00:06:34,544 --> 00:06:36,882
It's the size
of the United States ...
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00:06:36,965 --> 00:06:42,095
and the biggest source of sand
and dust in the entire world.
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00:07:22,060 --> 00:07:25,440
Sandstorms like these
appear without warning ...
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00:07:25,524 --> 00:07:30,571
and reduce visibility for days
over areas the size of Britain.
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00:07:39,540 --> 00:07:45,298
Dromedaries, single-humped camels,
take these storms in their stride.
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00:07:48,384 --> 00:07:52,972
The heaviest sand rises only
a few metres above the ground,
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00:07:53,097 --> 00:07:58,521
but the dust can be blown
5,000 metres out into the sky.
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00:08:03,568 --> 00:08:07,490
The ferocious wind,
armed with grains of sand,
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00:08:07,616 --> 00:08:11,453
is the agent that shapes all deserts.
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00:08:20,505 --> 00:08:27,556
Reptiles have armoured scaly skins
that protect them from the stinging grains.
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00:08:29,642 --> 00:08:34,772
For insects, the bombardment
can be very severe indeed.
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00:08:36,609 --> 00:08:39,820
The only escape
is below the surface.
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00:08:56,841 --> 00:09:01,054
As the winds rise and fall,
swallow and eddy,
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00:09:01,179 --> 00:09:04,724
so they pile the sand into dunes.
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00:09:08,397 --> 00:09:12,567
These sand scenes can be
hundreds of miles across.
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00:09:16,865 --> 00:09:21,745
In Namibia, the winds have built some
of the biggest dunes in the world.
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00:09:29,463 --> 00:09:33,718
Star dunes like these
can be 300 metres high.
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00:09:33,801 --> 00:09:38,641
Grains, swept up the flanks, are
blown off the crests of the ridges,
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00:09:38,725 --> 00:09:41,477
so it's only the tops
that are moving.
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00:09:48,361 --> 00:09:54,701
The main body of these dunes
may not have shifted for 5,000 years.
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00:10:06,008 --> 00:10:12,514
Few rocks can resist the continuous
blast of the sand carrying wind.
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00:10:12,681 --> 00:10:17,647
These outcrops are standing
in Egypt's White Desert.
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00:10:18,022 --> 00:10:20,983
But they will not do so
for much longer.
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00:10:22,485 --> 00:10:24,987
They're being inexorably
chiseled away ...
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00:10:25,072 --> 00:10:28,159
and turned into more sand.
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00:11:07,415 --> 00:11:14,797
Now lumps of heavily eroded rocks
have been marooned in a sea of sand.
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00:11:31,776 --> 00:11:35,449
These jagged pyramids
a hundred metres tall,
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00:11:35,574 --> 00:11:39,202
were once part
of a continuous rocky plateau.
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00:11:39,328 --> 00:11:43,957
The blasting sand will eventually
eliminate them altogether.
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00:11:52,259 --> 00:11:54,193
The relentless power of the
wind ...
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00:11:54,287 --> 00:11:58,768
ensures that the face of a desert
is continually changing.
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00:11:58,851 --> 00:12:02,271
But there is one constant presence —
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00:12:10,073 --> 00:12:11,991
the desert sun.
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00:12:26,635 --> 00:12:30,222
The sun's heat and power
to evaporate water ...
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00:12:30,347 --> 00:12:36,522
has had a profound effect on the bodies
and habits of everything that lives here.
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00:12:40,275 --> 00:12:43,821
This sun potentially is a killer.
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00:12:45,157 --> 00:12:49,245
And the red kangaroos
must acknowledge that.
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00:12:50,371 --> 00:12:52,623
Right now, while the sun is low,
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00:12:52,748 --> 00:12:56,004
there's no immediate cause
for concern.
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00:12:56,587 --> 00:12:59,799
But this situation won't last long.
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00:13:00,591 --> 00:13:07,100
Australia is the world's most arid continent
with blistering daytime temperatures.
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00:13:14,065 --> 00:13:20,157
Every hour, the temperature rises
by 5 degrees centigrade.
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00:13:26,749 --> 00:13:31,170
Soon the heat will reach
a critical point.
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00:13:40,639 --> 00:13:46,856
Any kangaroo out in the open
is in serious danger of overheating.
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00:13:52,320 --> 00:13:58,745
In the full sun, the temperature
on the ground soars to 70 degrees.
100
00:14:02,999 --> 00:14:08,757
By midday, the radiation is
so intense they must take shelter.
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00:14:29,115 --> 00:14:32,743
In the shade they're shielded
from much of the sun's energy,
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00:14:32,868 --> 00:14:35,832
but their body temperature
can still rise.
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00:14:38,543 --> 00:14:42,213
So they lick saliva
on to their forearms ...
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00:14:42,296 --> 00:14:46,386
where there is a network of blood vessels
close to the surface of the skin ...
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00:14:46,469 --> 00:14:51,182
and, as the saliva evaporates,
their blood is cooled.
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00:14:53,810 --> 00:14:58,608
This thermal image shows
just how effective the process is.
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00:14:58,734 --> 00:15:02,821
The blue areas on the body
are the cooler parts.
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00:15:11,623 --> 00:15:15,421
As the saliva dries
it has to be replaced,
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00:15:15,546 --> 00:15:19,842
and this is a real drain
on the kangaroo's body fluids.
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00:15:30,188 --> 00:15:34,150
Even in the shade
the earth is baking hot,
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00:15:34,776 --> 00:15:38,281
so the kangaroos dig away
the warmed topsoil ...
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00:15:38,365 --> 00:15:41,618
to get at the cooler ground beneath.
113
00:16:04,186 --> 00:16:08,859
By staying in the shade and licking
to control their body temperature,
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00:16:08,984 --> 00:16:12,196
kangaroos manage to get through
the hottest part of the day ...
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00:16:12,321 --> 00:16:13,948
without heat stroke.
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00:16:14,907 --> 00:16:17,453
But for the majority
of desert animals,
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00:16:17,537 --> 00:16:21,040
this strategy would not be
enough for survival.
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00:16:44,192 --> 00:16:49,199
The extraordinary ears of the
fennec foxes of Africa radiate heat,
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00:16:49,324 --> 00:16:52,786
but the animals have
another way of keeping cool.
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00:17:02,423 --> 00:17:04,800
They spend their days underground ...
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00:17:04,925 --> 00:17:07,972
and only emerge at sunset.
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00:17:20,028 --> 00:17:23,406
Darkness brings huge changes.
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00:17:23,531 --> 00:17:28,455
In the Sahara, the temperature can drop
as much as 30 degrees during the night,
124
00:17:28,580 --> 00:17:33,335
so it's cool enough to allow
these desert fox cubs to play.
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00:17:40,969 --> 00:17:43,597
All sorts of creatures now appear ...
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00:17:43,722 --> 00:17:46,977
including some really unexpected ones.
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00:17:49,939 --> 00:17:52,233
Toads have permeable skins ...
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00:17:52,316 --> 00:17:56,322
and would quickly die from desiccation
out in the daytime heat.
129
00:17:56,406 --> 00:17:59,033
It's only now that
they can leave shelter.
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00:18:02,036 --> 00:18:03,996
The same is true for scorpions,
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00:18:04,122 --> 00:18:07,752
even though their shells
are actually watertight.
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00:18:19,891 --> 00:18:23,812
In fact, most small desert
creatures are nocturnal —
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00:18:23,937 --> 00:18:26,150
so it's only now
that you can judge ...
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00:18:26,275 --> 00:18:29,528
just how much life
there can be in the desert.
135
00:18:30,446 --> 00:18:36,245
But moisture, lost even at night,
has to be replaced sometime somehow,
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00:18:36,370 --> 00:18:41,041
and that problem dominates
the lives of all desert dwellers.
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00:18:49,260 --> 00:18:51,596
The Atacama in Chile.
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00:18:51,679 --> 00:18:55,225
This is the driest desert
in the world.
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00:18:56,853 --> 00:18:59,898
Some parts may not see rain
for 50 years,
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00:18:59,981 --> 00:19:01,357
and with such a record ...
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00:19:01,441 --> 00:19:05,280
you'd expect the place
to be completely barren.
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00:19:10,243 --> 00:19:14,623
These are South America's camels,
guanacos.
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00:19:16,085 --> 00:19:18,420
They're very good
at conserving moisture,
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00:19:18,545 --> 00:19:21,924
but they nonetheless
need a regular supply of water.
145
00:19:34,939 --> 00:19:38,236
They get it partly
from cactus flowers,
146
00:19:38,319 --> 00:19:41,989
but that explanation
raises another question.
147
00:19:44,242 --> 00:19:47,831
How do the cacti
survive without rain?
148
00:19:54,629 --> 00:19:59,970
Hot winds suck all the moisture
from the surface of the land.
149
00:20:01,346 --> 00:20:06,478
Clearly, there must be something else
that takes the place of rain.
150
00:20:07,771 --> 00:20:13,819
The secret is a cold sea current
that runs parallel to the land.
151
00:20:30,798 --> 00:20:34,218
The cold water cools
the moist warm air above it ...
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00:20:34,343 --> 00:20:37,390
and that produces banks of fog.
153
00:21:00,626 --> 00:21:07,802
At the same time, wind blowing
on to the shore, sweeps the fog inland.
154
00:21:22,610 --> 00:21:27,450
Before long, the cacti
are dripping with dew.
155
00:21:35,961 --> 00:21:37,963
The fog is so regular,
156
00:21:38,088 --> 00:21:41,675
that moisture loving lichens
are able to grow on the cacti ...
157
00:21:41,800 --> 00:21:45,138
and they absorb liquid
like a sponge.
158
00:21:47,599 --> 00:21:50,352
In the land of almost no rain,
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00:21:50,477 --> 00:21:56,277
these precious drops are life-savers
for many different creatures.
160
00:22:04,869 --> 00:22:10,835
Further inland, the air remains so warm
that its moisture does not condense,
161
00:22:10,918 --> 00:22:15,592
so this slender strip of desert is
virtually the only part of the Atacama ...
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00:22:15,717 --> 00:22:17,760
where life can exist.
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00:22:21,990 --> 00:22:23,550
And without the fog,
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00:22:24,100 --> 00:22:26,813
this land, too, would be empty.
165
00:22:40,537 --> 00:22:43,749
The guanacos make
the most of the dew,
166
00:22:43,874 --> 00:22:46,712
but it will not remain
for long.
167
00:22:47,421 --> 00:22:50,341
In an hour or two,
the sun will have burnt it off ...
168
00:22:50,466 --> 00:22:53,052
and dried the surface of the cacti.
169
00:23:01,938 --> 00:23:07,445
The Sonoran desert in Arizona,
is not quite so dry as the Atacama —
170
00:23:07,570 --> 00:23:09,781
some rain does fall.
171
00:23:10,615 --> 00:23:12,325
But it is infrequent,
172
00:23:12,408 --> 00:23:13,910
and when it does arrive,
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00:23:13,993 --> 00:23:17,874
animals and plants have
to be ready to make the most of it.
174
00:23:19,334 --> 00:23:21,086
And it's coming.
175
00:23:29,763 --> 00:23:31,932
When the summer monsoon blows in,
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00:23:32,057 --> 00:23:35,604
the giant saguaros,
one of the biggest of all cacti,
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00:23:35,688 --> 00:23:38,440
are ready to take
full advantage of it.
178
00:24:12,689 --> 00:24:19,364
After a rainstorm, the saguaro's long
shallow root system sucks up the water,
179
00:24:19,448 --> 00:24:24,536
and the pleats on its trunk
enable it to expand rapidly.
180
00:24:32,463 --> 00:24:37,887
When full, a saguaro stem can store
up to 5 tonnes of water,
181
00:24:38,012 --> 00:24:42,517
and that's enough to see it
through many months of drought.
182
00:24:46,731 --> 00:24:52,445
The trunks of these huge plants
provide homes for the gila woodpecker.
183
00:24:54,489 --> 00:25:01,164
But birds are not the only animals
to benefit from the presence of the cacti.
184
00:25:17,518 --> 00:25:19,478
During four weeks of the summer,
185
00:25:19,603 --> 00:25:25,277
the saguaros bloom at night
to attract visitors.
186
00:25:28,281 --> 00:25:31,576
The pollen and nectar with which
these flowers are loaded,
187
00:25:31,701 --> 00:25:35,999
attract long-nosed
and long-tongued bats.
188
00:25:51,224 --> 00:25:56,398
The bats left Mexico a few days earlier
to escape the heat of summer ...
189
00:25:56,523 --> 00:26:00,777
and are on their way north
to the southern United States.
190
00:26:02,613 --> 00:26:06,744
To get there, they have
to cross the Sonoran desert.
191
00:26:12,541 --> 00:26:14,668
But the desert is so big ...
192
00:26:14,793 --> 00:26:18,424
that for most of the year
they would be unable to cross it.
193
00:26:18,549 --> 00:26:20,927
Now, with the saguaro in bloom,
194
00:26:21,052 --> 00:26:23,846
they can refuel on the way.
195
00:26:33,691 --> 00:26:37,697
So the saguaro's success in
developing a way to store water ...
196
00:26:37,822 --> 00:26:45,624
is now crucial to most of the animals
that live or even travel through this land.
197
00:27:24,419 --> 00:27:29,134
The scarcity of rain determined
the shape of this icon of the desert,
198
00:27:29,259 --> 00:27:31,303
but water, scarce thought it is,
199
00:27:31,428 --> 00:27:35,601
has also, like the wind,
shaped the land itself.
200
00:27:52,786 --> 00:27:54,663
In the deserts of Utah,
201
00:27:54,788 --> 00:28:00,504
ancient rivers flowing across sandstone
country, steadily widen their canyons ...
202
00:28:00,630 --> 00:28:07,055
until now the land between them
has been reduced to spires and pinnacles.
203
00:28:36,674 --> 00:28:41,929
With little or no soil to retain
the water on the surface of the land,
204
00:28:42,054 --> 00:28:45,183
life here is scarce indeed.
205
00:28:46,811 --> 00:28:48,854
And when resources are limited,
206
00:28:48,980 --> 00:28:51,566
conflict is never far away.
207
00:29:02,203 --> 00:29:04,914
These are Nubian ibex,
208
00:29:05,039 --> 00:29:07,836
and they are squaring up
for a duel.
209
00:29:14,092 --> 00:29:15,554
And when trouble starts,
210
00:29:15,679 --> 00:29:21,184
a smart ibex knows that the best thing
to do is to gain higher ground.
211
00:29:38,539 --> 00:29:41,834
These are actually
subordinate male ibex,
212
00:29:41,959 --> 00:29:44,462
but their fights
are nonetheless serious.
213
00:29:44,545 --> 00:29:49,802
Losing one might mean
never getting the chance to breed ever.
214
00:30:12,162 --> 00:30:15,709
When competitors are evenly
matched as they are here,
215
00:30:15,834 --> 00:30:18,837
duels can last for an hour.
216
00:30:38,653 --> 00:30:42,991
In this heat the effort
is truly exhausting.
217
00:30:44,826 --> 00:30:51,334
But victory here will gain important
ranking points on a male's way to the top.
218
00:31:22,622 --> 00:31:24,290
There's so much at stake,
219
00:31:24,415 --> 00:31:26,711
that not all play fair.
220
00:31:41,978 --> 00:31:44,397
The battle has produced the winner,
221
00:31:44,522 --> 00:31:48,570
but the ultimate prize
is not his yet.
222
00:31:52,032 --> 00:31:56,330
That currently belongs
to the dominant male ibex.
223
00:31:58,499 --> 00:32:02,586
His rank earns him the loyalty
of a harem of females ...
224
00:32:02,711 --> 00:32:06,342
and they follow him closely
as he travels across this desert ...
225
00:32:06,467 --> 00:32:08,636
searching for food and water.
226
00:32:10,805 --> 00:32:13,891
He doesn't have to waste time
looking for mates —
227
00:32:14,016 --> 00:32:15,603
they're his for the taking,
228
00:32:15,728 --> 00:32:20,608
so he can concentrate with them
on keeping fit and healthy.
229
00:32:35,961 --> 00:32:39,047
Lizards are desert specialists.
230
00:32:42,134 --> 00:32:45,973
But here, their numbers
are extraordinary.
231
00:32:51,395 --> 00:32:53,557
These crevices in South Africa ...
232
00:32:53,645 --> 00:32:57,653
contain the highest density
of lizards in the world.
233
00:33:07,498 --> 00:33:11,169
They're called flat lizards
for obvious reasons,
234
00:33:11,294 --> 00:33:16,301
and they flaunt their multi-coloured
bellies in territorial disputes.
235
00:33:18,762 --> 00:33:20,263
He's made his point,
236
00:33:20,388 --> 00:33:23,308
and now it's time
to find some food.
237
00:33:25,143 --> 00:33:26,688
As the day warms up,
238
00:33:26,813 --> 00:33:29,066
the lizards move away
from their cracks ...
239
00:33:29,191 --> 00:33:31,860
and head down
to the bottom of the gorge.
240
00:33:33,111 --> 00:33:35,323
Their goal is the river.
241
00:33:37,743 --> 00:33:40,162
There is no food at the edge,
242
00:33:40,287 --> 00:33:43,999
but this desert river
holds a secret.
243
00:33:50,508 --> 00:33:56,057
Each day, blackfly rise from
turbulent stretches of the river.
244
00:33:56,140 --> 00:33:59,018
This is what the lizards
have come for.
245
00:34:14,160 --> 00:34:16,290
The black fly never land,
246
00:34:16,415 --> 00:34:20,085
so the lizards have to leap
for their food.
247
00:34:32,349 --> 00:34:38,774
In one day, each of these acrobatic
little lizards may catch 50 flies.
248
00:34:48,953 --> 00:34:51,289
There are plenty of flies
to go round,
249
00:34:51,414 --> 00:34:54,876
even with hundreds of lizards
competing for them.
250
00:35:08,769 --> 00:35:10,558
Away from these rapids,
251
00:35:10,669 --> 00:35:15,025
flat lizard populations
are found in much smaller numbers.
252
00:35:15,150 --> 00:35:20,157
But here, one unusual abundance
has produced another.
253
00:35:31,212 --> 00:35:34,215
Deserts are created
by the lack of water,
254
00:35:34,340 --> 00:35:38,638
but what actually kills animals
here is not heat or thirst,
255
00:35:38,763 --> 00:35:40,723
but lack of food.
256
00:35:59,162 --> 00:36:03,292
So, how on earth does
a plant-eater this size ...
257
00:36:03,417 --> 00:36:09,216
survive in a place apparently
totally devoid of vegetation?
258
00:36:15,474 --> 00:36:19,603
Elephants in Namibia
are the toughest in Africa.
259
00:36:19,729 --> 00:36:21,689
And they need to be.
260
00:36:38,793 --> 00:36:42,047
What little food exists
is so dispersed,
261
00:36:42,172 --> 00:36:45,216
that these elephants walk
up to 50 miles a day ...
262
00:36:45,343 --> 00:36:51,099
as they travel up the dry river channels
searching for something to eat.
263
00:37:05,785 --> 00:37:10,039
At times the task
looks truly helpless.
264
00:37:44,788 --> 00:37:48,544
Elephants may seem out of place
in this landscape,
265
00:37:48,669 --> 00:37:51,338
but they're not the only ones.
266
00:38:07,775 --> 00:38:11,529
Amazingly, lions live here, too.
267
00:38:16,077 --> 00:38:20,165
In savanah country, huge herds
of games support prides ...
268
00:38:20,290 --> 00:38:22,876
containing 20 lions or more.
269
00:38:23,001 --> 00:38:26,882
But to live here, lions have had
to change their habits —
270
00:38:27,007 --> 00:38:28,717
prides are much smaller ...
271
00:38:28,842 --> 00:38:31,887
and their home ranges
are very much bigger.
272
00:38:32,888 --> 00:38:35,350
And there's an added problem —
273
00:38:36,685 --> 00:38:40,272
their food is always on the move.
274
00:38:48,908 --> 00:38:50,326
Like the elephants,
275
00:38:50,451 --> 00:38:55,415
the lions must travel great distances
to find enough to live on.
276
00:39:10,642 --> 00:39:13,436
But lions can't go everywhere —
277
00:39:13,561 --> 00:39:17,901
they won't attempt to cross
this field of sand dunes ...
278
00:39:18,026 --> 00:39:19,945
and the oryx know it.
279
00:40:19,892 --> 00:40:23,979
The lions must wait for the oryx
to leave the safety of the dunes,
280
00:40:24,104 --> 00:40:27,068
which eventually they must
to find food and water.
281
00:40:27,193 --> 00:40:29,653
And then the lions
will ambush them.
282
00:41:35,441 --> 00:41:39,863
The elephants have found
some of their favourite food.
283
00:41:46,455 --> 00:41:49,499
Grasses are the staple diet
of all elephants,
284
00:41:49,624 --> 00:41:53,003
but this herd concentrates
on digging up the roots,
285
00:41:53,128 --> 00:41:57,259
which have more nutrition
and moisture than the stems.
286
00:41:57,384 --> 00:41:58,802
It's the sort of behaviour ...
287
00:41:58,927 --> 00:42:03,140
that can make all the difference
in a place of serious shortages.
288
00:42:03,849 --> 00:42:07,646
Yet all this can change
in an instant.
289
00:42:24,791 --> 00:42:29,589
The fortunes of many deserts
are ruled by distant rains.
290
00:42:29,714 --> 00:42:35,095
This water fell as rain in mountains
more than a hundred miles away.
291
00:42:40,602 --> 00:42:42,479
It's known as a "flash flood" ...
292
00:42:42,604 --> 00:42:46,944
and called that because the water
may run for just a single day.
293
00:42:47,069 --> 00:42:51,782
It's an event that only happens
once or twice a year at the most.
294
00:43:12,598 --> 00:43:17,021
The sandy riverbed acts like a
giant strip of blotting paper ...
295
00:43:17,147 --> 00:43:20,442
sucking up the water
as soon as it appears.
296
00:43:29,953 --> 00:43:33,415
But every square metre of soil
moistened by this river ...
297
00:43:33,540 --> 00:43:38,046
will increase the chances
of survival for those that live here.
298
00:43:43,677 --> 00:43:47,058
Waterholes are filled temporarily.
299
00:43:51,729 --> 00:43:55,232
Elsewhere in Africa,
elephants drink every day,
300
00:43:55,358 --> 00:43:56,903
but the lack of water here,
301
00:43:57,028 --> 00:44:00,149
means that desert elephants
can only refill their tanks ...
302
00:44:00,294 --> 00:44:03,743
once every 4 or 5 days.
303
00:44:04,869 --> 00:44:09,167
Within a week, the flash flood
has produced a flush of green,
304
00:44:09,292 --> 00:44:13,588
more than enough to draw
the oryx out of the dunes.
305
00:44:15,466 --> 00:44:19,554
It's a rare chance for them
to build up their food reserves.
306
00:44:28,190 --> 00:44:32,736
The flood has made life easier
for the lions, too.
307
00:44:35,114 --> 00:44:40,204
The flesh of this oryx will keep the
family going for a week at the most.
308
00:44:40,329 --> 00:44:42,790
But for a while,
the hunting will be easier,
309
00:44:42,915 --> 00:44:46,045
now that river channel
has turned green.
310
00:44:50,007 --> 00:44:52,844
The good times
for lions and oryx are brief,
311
00:44:53,010 --> 00:44:55,012
but these are
the short moments ...
312
00:44:55,138 --> 00:44:59,269
that make it possible to live
in deserts the year round.
313
00:45:05,024 --> 00:45:08,113
"Death Valley" is the hottest
place on Earth.
314
00:45:08,238 --> 00:45:12,492
Yet even this furnace
can be transformed by water.
315
00:45:23,088 --> 00:45:25,343
A single shower can enable
seeds ...
316
00:45:25,448 --> 00:45:28,137
that have lain dormant
for 30 years or more ...
317
00:45:28,262 --> 00:45:30,389
to burst into life.
318
00:45:38,775 --> 00:45:43,196
And there hasn't been a bloom
like this one for a century.
319
00:45:55,419 --> 00:45:59,091
The periods of boom
in Death Valley are short.
320
00:45:59,216 --> 00:46:03,470
but they're just frequent enough
to keep life ticking over.
321
00:46:12,022 --> 00:46:16,654
A sudden flush of vegetation is
what every desert dweller waits for,
322
00:46:16,779 --> 00:46:20,074
and when it happens,
they must make the most of it.
323
00:46:40,557 --> 00:46:42,892
There is no other species
on the planet ...
324
00:46:43,017 --> 00:46:46,925
that responds as quickly and as
dramatically to the good times ...
325
00:46:47,017 --> 00:46:49,985
as the desert locust.
326
00:46:50,318 --> 00:46:55,450
Eggs, that have remained in the ground
for 20 years, begin to hatch.
327
00:47:08,090 --> 00:47:10,217
The young locusts
are known as hoppers,
328
00:47:10,342 --> 00:47:12,678
for at this stage
they're flightless.
329
00:47:12,928 --> 00:47:19,520
They find new feeding grounds by
following the smell of sprouting grass.
330
00:47:25,360 --> 00:47:29,324
Normally, it takes 4 weeks
for hoppers to become adults,
331
00:47:29,449 --> 00:47:31,951
but when the conditions
are right as now,
332
00:47:32,076 --> 00:47:35,832
their development switches
to the fast track.
333
00:47:40,837 --> 00:47:44,049
As the vegetation in one place
begins to run out,
334
00:47:44,174 --> 00:47:47,721
the winged adults release
pheromones — scent messages,
335
00:47:47,846 --> 00:47:51,391
which tell others in the group
that they must move on.
336
00:48:03,364 --> 00:48:04,949
And when groups merge,
337
00:48:05,074 --> 00:48:07,328
they form a swarm.
338
00:48:29,938 --> 00:48:34,067
An adult locust eats
its entire body weight every day,
339
00:48:34,192 --> 00:48:35,501
and a whole swarm ...
340
00:48:35,692 --> 00:48:39,741
can consume literally hundreds
of tonnes of vegetation.
341
00:48:41,285 --> 00:48:43,579
They have to keep on moving.
342
00:48:45,038 --> 00:48:47,251
The swarm travels with the wind —
343
00:48:47,334 --> 00:48:50,754
it's the most energy-saving
way of flying.
344
00:48:54,341 --> 00:48:56,201
Following the flow of wind ...
345
00:48:56,291 --> 00:48:59,891
means that they're always heading
toward areas of low pressure,
346
00:49:00,016 --> 00:49:05,397
places where wind meets rain
and vegetation starts to grow.
347
00:49:07,317 --> 00:49:08,318
As they fly,
348
00:49:08,443 --> 00:49:11,112
swarms join up
with other swarms ...
349
00:49:11,237 --> 00:49:15,200
to form gigantic plagues
several billions strong ...
350
00:49:15,326 --> 00:49:17,871
and as much as 40 miles wide.
351
00:49:19,915 --> 00:49:24,503
They will consume every edible
thing that lies in their path.
352
00:49:37,853 --> 00:49:42,024
This is one of planet Earth's
greatest spectacles.
353
00:49:42,149 --> 00:49:44,109
It's rarely seen on this scale ...
354
00:49:44,235 --> 00:49:46,280
and it won't last long.
355
00:49:46,405 --> 00:49:48,074
Once the food is gone,
356
00:49:48,199 --> 00:49:52,121
the steady roar of a billion
beating locust wings,
357
00:49:52,249 --> 00:49:54,121
will once again be replaced ...
358
00:49:54,247 --> 00:49:58,920
by nothing more than the
sound of the desert wind.
9999
00:00:0,500 --> 00:00:2,00
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