1
00:00:25,760 --> 00:00:30,240
Crocodiles and alligators are
among the world's great survivors.

2
00:00:33,480 --> 00:00:37,520
They've been around in one form or
another for over 200 million years.

3
00:00:37,520 --> 00:00:42,200
And in that time they've weathered
the worst the planet could throw
at them.

4
00:00:45,440 --> 00:00:49,160
These ancient animals seem
almost indestructible.

5
00:00:49,160 --> 00:00:52,600
But where do they get their
extraordinary staying power?

6
00:00:52,600 --> 00:00:57,560
What makes crocodilians
such phenomenal survivors?

7
00:01:00,640 --> 00:01:05,960
The crocodilians are the most deadly
inland water predators on Earth,

8
00:01:05,960 --> 00:01:09,200
the best known of
the reptilian giants.

9
00:01:18,000 --> 00:01:21,120
Crocodilians are built to last.

10
00:01:25,400 --> 00:01:31,640
Clues to their success lie in their
history, their behaviour
and the way their bodies work.

11
00:01:31,640 --> 00:01:35,480
How has King Croc
held his throne so long?

12
00:01:55,040 --> 00:02:01,160
The crocodilians dominate
the world's tropical freshwaters
and tidal estuaries.

13
00:02:01,160 --> 00:02:06,760
They include the gharials,
crocodiles, alligators, and cayman.

14
00:02:06,760 --> 00:02:11,760
23 species rule the
swamps, rivers and lakes of Asia,

15
00:02:11,760 --> 00:02:14,680
Africa, Australia and the Americas.

16
00:02:16,640 --> 00:02:18,960
They come in many shapes and sizes,

17
00:02:18,960 --> 00:02:23,960
but are modelled on the same basic
and highly durable design.

18
00:02:27,720 --> 00:02:32,760
Around 100 million years ago
the ancestors of living crocodilians

19
00:02:32,760 --> 00:02:37,400
hit on the ideal blueprint
for a water-based stealth predator -

20
00:02:37,400 --> 00:02:41,440
a winning formula that their
descendants still exploit today.

21
00:02:46,640 --> 00:02:52,880
Their elongated, streamlined body
can slide silently and
smoothly through the water.

22
00:02:54,920 --> 00:03:01,400
Their huge muscular flattened tail
provides a powerful
thrust for swimming.

23
00:03:10,440 --> 00:03:13,920
A stealth hunter
relies on keeping a low profile.

24
00:03:13,920 --> 00:03:18,760
A croc can travel fast
without revealing its presence.

25
00:03:26,920 --> 00:03:31,120
Short legs can be tucked in tight
against the body to minimise drag,

26
00:03:31,120 --> 00:03:34,360
or splayed out to act as stabilisers.

27
00:03:38,200 --> 00:03:41,600
Beneath their primitive-looking
exterior

28
00:03:41,600 --> 00:03:44,760
lies a crucial mix
of flexibility and strength.

29
00:03:47,080 --> 00:03:52,040
The vertebrae in the spine
are shaped for maximum mobility.

30
00:03:56,280 --> 00:04:02,400
Special interlocking processes
in the neck vertebrae increase
their strength and rigidity,

31
00:04:02,400 --> 00:04:05,440
helping the croc
to hold on to large, powerful prey.

32
00:04:10,480 --> 00:04:15,200
The shape of their head and back
allows them to break the water
surface with barely a ripple.

33
00:04:17,720 --> 00:04:20,720
Most of the body
remains concealed underwater

34
00:04:20,720 --> 00:04:25,200
but eyes set high on the head
are a periscope on the world around.

35
00:04:29,920 --> 00:04:35,920
As aquatic predators, crocodilians
need to be able to open their mouth
underwater

36
00:04:35,920 --> 00:04:37,880
without risk of drowning.

37
00:04:43,120 --> 00:04:46,920
When their head is submerged,
a valve at the back of the tongue

38
00:04:46,920 --> 00:04:50,960
completely seals the throat and stops
water pouring down into the lungs.

39
00:04:54,640 --> 00:05:01,480
In addition, air tubes open behind
this valve and run to the nostrils,
enabling crocodilians to breathe

40
00:05:01,480 --> 00:05:04,600
as they lie concealed
below the water surface.

41
00:05:08,480 --> 00:05:14,280
Crocodilians combine protective
armour with great sensitivity.

42
00:05:14,280 --> 00:05:17,960
Their scales are studded with tiny
pressure receptors

43
00:05:17,960 --> 00:05:21,440
that pick up the minutest disturbance
in the water.

44
00:05:26,040 --> 00:05:31,800
Even a falling seedpod
can trigger a response.

45
00:05:31,800 --> 00:05:36,880
At over six metres long, this is the
largest of all modern crocodilians,

46
00:05:36,880 --> 00:05:39,680
the Australian saltwater crocodile.

47
00:05:46,680 --> 00:05:51,160
For a water-based predator
fruit bats are tricky prey.

48
00:05:51,160 --> 00:05:56,160
The crocodile's best tactic
is an ambush attack.

49
00:06:07,640 --> 00:06:10,920
In the murky waters,
it repositions

50
00:06:10,920 --> 00:06:13,080
and waits for the
right moment to strike.

51
00:06:24,440 --> 00:06:26,920
It can afford to be patient,

52
00:06:26,920 --> 00:06:30,520
thanks to one of the most
sophisticated elements of its design.

53
00:06:39,480 --> 00:06:43,840
During a dive,
crocodilian blood is more efficient

54
00:06:43,840 --> 00:06:47,840
than that of any other animal at
delivering oxygen to the tissues,

55
00:06:47,840 --> 00:06:52,880
and a special valve in the croc's
heart can divert blood from
non-essential body areas

56
00:06:52,880 --> 00:06:55,080
to where it's needed most.

57
00:06:59,560 --> 00:07:03,680
By reducing its heart rate
and rationing its oxygen,

58
00:07:03,680 --> 00:07:06,800
the croc can hold its breath
for an hour or more,

59
00:07:06,800 --> 00:07:11,320
and play a waiting game
that would kill us.

60
00:07:11,320 --> 00:07:17,920
Underwater, a transparent third
eyelid closes to protect the eye.

61
00:07:17,920 --> 00:07:23,520
Back at the surface,
full sight is restored.

62
00:07:23,520 --> 00:07:26,520
130 degrees of widescreen vision

63
00:07:26,520 --> 00:07:31,360
means the croc can monitor
the slightest movement.

64
00:07:31,360 --> 00:07:31,400
And a binocular view
lets it judge distance accurately.

65
00:07:31,480 --> 00:07:35,160
All these adaptations
help to make the crocodilians
masters of the surprise attack.

66
00:07:49,720 --> 00:07:54,120
The muscular tail provides
power and drive to launch
the all-important strike.

67
00:08:26,440 --> 00:08:31,240
Crocodilians are at the pinnacle
of amphibious predator design.

68
00:08:31,240 --> 00:08:35,720
But this alone is not enough
to explain their enduring success.

69
00:08:37,800 --> 00:08:41,240
Something else has helped
crocodilians flourish

70
00:08:41,240 --> 00:08:45,320
in the largely poor and unpredictable
habitats in which they live -

71
00:08:45,320 --> 00:08:48,360
engine design.

72
00:08:50,160 --> 00:08:54,640
South America's freshwater
rivers and lakes are home to many
kinds of animal.

73
00:08:56,880 --> 00:09:03,320
Like all living creatures, they're
powered by internal flesh and blood
combustion engines.

74
00:09:03,320 --> 00:09:05,760
But while some engines are slow,

75
00:09:05,760 --> 00:09:10,800
others have a fast idling speed
and are tuned for high performance.

76
00:09:23,520 --> 00:09:27,920
Black cayman and giant
otters share the same space

77
00:09:27,920 --> 00:09:33,360
but their very different body engines
dictate very different ways of life.

78
00:09:33,360 --> 00:09:37,440
The basic mechanics, however,
are the same.

79
00:09:37,440 --> 00:09:42,240
Oxygen breathed in with air
is carried in the blood to
all the body's cells.

80
00:09:45,480 --> 00:09:50,200
Inside each cell this oxygen
reacts with digested food,

81
00:09:50,200 --> 00:09:52,640
the body's fuel, releasing energy.

82
00:09:55,240 --> 00:09:59,600
Some energy is spent
on growing and getting around.

83
00:09:59,600 --> 00:10:03,960
Some is stored inside muscles
for future use

84
00:10:03,960 --> 00:10:06,760
And some is converted into heat.

85
00:10:11,200 --> 00:10:15,640
The faster, high performance
engines of the giant otters

86
00:10:15,640 --> 00:10:19,160
burn a lot of fuel quickly,
and generate a lot of heat.

87
00:10:19,160 --> 00:10:24,000
So much heat that the otters can
run an internal heating system,

88
00:10:24,000 --> 00:10:26,280
which keeps their bodies permanently
warm.

89
00:10:26,280 --> 00:10:30,440
It's why they, like all mammals,
are called warm-blooded.

90
00:10:38,080 --> 00:10:40,760
The caymans' engines
work in a similar way,

91
00:10:40,760 --> 00:10:43,040
but with one vital difference.

92
00:10:44,800 --> 00:10:49,400
Their slow idling engines just don't
generate as much heat...

93
00:10:53,840 --> 00:10:57,880
..certainly not enough to keep
their bodies permanently warm,

94
00:10:57,880 --> 00:11:03,880
which is why cayman, like all
reptiles, are referred to
as being cold-blooded.

95
00:11:12,680 --> 00:11:15,720
One of the benefits of
a high performance engine,

96
00:11:15,720 --> 00:11:19,920
a high metabolism,
is a constant, warm body temperature.

97
00:11:27,600 --> 00:11:30,840
Being warm-blooded means that
you can live almost anywhere.

98
00:11:30,840 --> 00:11:34,880
You can stay warm
whatever the temperature outside.

99
00:11:34,880 --> 00:11:40,640
It's why mammals and birds are able
to live anywhere in the world, even
in the coldest places.

100
00:11:54,680 --> 00:11:58,400
Cold-blooded reptiles like
crocodilians, on the other hand,

101
00:11:58,400 --> 00:12:04,480
have to rely on an external source
of heat to rev up their bodies
and keep them running properly.

102
00:12:04,480 --> 00:12:07,080
They're solar-powered.

103
00:12:14,840 --> 00:12:20,080
Special bony discs along the
crocodilian's back act like solar
panels,

104
00:12:20,080 --> 00:12:24,160
absorbing heat and
downloading it into the bloodstream.

105
00:12:30,920 --> 00:12:35,080
If a crocodilian's body temperature
falls too low it becomes sluggish.

106
00:12:35,080 --> 00:12:39,920
Too high and it risks
heat exhaustion, even death.

107
00:12:48,000 --> 00:12:51,960
To warm up and cool down as their
body demands, they have to move

108
00:12:51,960 --> 00:12:55,720
between sunlight and shade
and from land to water.

109
00:12:58,640 --> 00:13:05,040
Being so dependent on the sun's heat
means crocodilians are restricted
to the warmer regions of the world.

110
00:13:12,720 --> 00:13:15,880
They simply can't survive
anywhere else.

111
00:13:18,800 --> 00:13:25,760
It's the downside of having a low
performance engine, a low metabolism,
but there is an upside -

112
00:13:25,760 --> 00:13:27,760
fuel economy.

113
00:13:29,760 --> 00:13:35,000
A slow, idling engine consumes less,
so fuel needs are slashed.

114
00:13:37,840 --> 00:13:44,360
The fast, gas-guzzling engines
of the giant otters burn huge
quantities of fuel and oxygen

115
00:13:44,360 --> 00:13:46,800
and they need constant refuelling.

116
00:13:55,040 --> 00:13:58,520
A huge 80% of all the food
the otters eat

117
00:13:58,520 --> 00:14:02,600
is turned straight into heat
to keep them warm.

118
00:14:04,320 --> 00:14:08,160
So they spend much of their time
hunting just to stay alive

119
00:14:08,160 --> 00:14:11,960
and support their high
octane, full throttle lifestyle.

120
00:14:14,440 --> 00:14:20,520
But the slow-performance
crocodilians focus on fuel economy.

121
00:14:25,920 --> 00:14:32,320
They don't need so much food
and they only expend energy
when absolutely necessary.

122
00:14:32,320 --> 00:14:36,160
It means they can often afford
to wait for food to come to them.

123
00:14:44,440 --> 00:14:50,040
All crocodilians are capable
of a last-minute burst of energy
to nail their victim,

124
00:14:50,040 --> 00:14:54,520
but unlike a mammal they simply can't
sustain such activity for long.

125
00:14:54,520 --> 00:14:57,280
A few minutes
and they're completely exhausted.

126
00:15:16,920 --> 00:15:22,120
Crocodilians don't use the
majority of their food for heating,

127
00:15:22,120 --> 00:15:25,440
they turn it into more body mass,
more croc.

128
00:15:25,440 --> 00:15:29,240
One good kill will last for months.

129
00:15:57,040 --> 00:16:03,400
This strategy has served crocs
well in the unpredictable
environments in which they live.

130
00:16:03,400 --> 00:16:09,000
In parts of India, rivers, lakes
and swamps can swing between
extremes of drought and flood.

131
00:16:15,000 --> 00:16:22,320
To survive here
you need to be able to make the most
of good times and endure the bad.

132
00:16:22,320 --> 00:16:24,560
It's something crocodilians,

133
00:16:24,560 --> 00:16:31,400
like the great marsh mugger
crocodiles of India and Sri Lanka,
have evolved to do extremely well.

134
00:16:35,120 --> 00:16:39,960
As drought approaches,
water levels start to drop.

135
00:16:41,600 --> 00:16:46,440
As lakes and swamps dry up, not only
are the crocs unable to hunt for
food,

136
00:16:46,440 --> 00:16:50,400
they also lose the cool water that
helps them regulate their body
temperature.

137
00:17:02,120 --> 00:17:08,920
As his kingdom literally
vanishes before his eyes,
how will King Croc cope now?

138
00:17:22,800 --> 00:17:25,840
When the situation reaches crisis
point,

139
00:17:25,840 --> 00:17:30,880
the muggers leave their shrinking
pools and strike out on their own,

140
00:17:30,880 --> 00:17:33,720
on a life and death expedition
over land.

141
00:17:53,160 --> 00:18:00,080
It's thought that mugger crocodiles
can travel up to 10km each night
in search of water.

142
00:18:00,080 --> 00:18:03,800
If necessary, they can lie
up in shade during the day.

143
00:18:14,000 --> 00:18:17,360
This is the mugger
at its most vulnerable.

144
00:18:17,360 --> 00:18:23,080
Without access to water,
it could easily bake to death
before its journey's end.

145
00:18:29,920 --> 00:18:35,160
But with no water to be found
anywhere, rescue comes in another
form -

146
00:18:35,160 --> 00:18:38,160
underground.

147
00:18:41,960 --> 00:18:45,480
Sometimes muggers have to excavate
new burrows,

148
00:18:45,480 --> 00:18:49,040
but often, they
revisit ones dug in previous years.

149
00:18:56,240 --> 00:18:58,720
Down here it's cooler,

150
00:18:58,720 --> 00:19:04,440
and after an arduous time on the
road, the crocodile can, at last,
rest.

151
00:19:06,800 --> 00:19:10,880
But with no food available,
the mugger is facing starvation.

152
00:19:10,880 --> 00:19:14,040
Its body must begin to adapt.

153
00:19:24,040 --> 00:19:29,320
The mugger crocodile sinks into a
state of dormancy called aestivation.

154
00:19:36,280 --> 00:19:40,760
Its breathing begins to slow
and its heart rate falls.

155
00:19:42,600 --> 00:19:46,800
Even so, its body engine
continues to tick over,

156
00:19:46,800 --> 00:19:52,160
using up water and fat reserves
and generating toxic waste products.

157
00:20:08,000 --> 00:20:10,120
Entombed underground,

158
00:20:10,120 --> 00:20:15,160
this sleeping giant has to overcome
its body's biological demands.

159
00:20:15,160 --> 00:20:17,440
In ways not yet fully understood,

160
00:20:17,440 --> 00:20:22,560
it copes with not eating and drinking
or releasing waste for several
months.

161
00:20:31,320 --> 00:20:36,000
It plays the trademark
crocodilian waiting game.

162
00:20:50,400 --> 00:20:53,400
Eventually, the rains return.

163
00:21:21,800 --> 00:21:25,920
The mugger senses that the
world outside is reviving.

164
00:21:25,920 --> 00:21:27,880
It's time to emerge.

165
00:21:32,320 --> 00:21:38,480
This ability to withdraw from
the world when food is scarce
has served crocodilians well.

166
00:21:38,480 --> 00:21:42,840
Thanks to their slow performance
engine and their low metabolic rate,

167
00:21:42,840 --> 00:21:46,040
they can simply stop eating
and live off their reserves.

168
00:21:51,400 --> 00:21:55,640
This biological endurance has helped
crocodilians reign supreme

169
00:21:55,640 --> 00:22:00,000
over some of the most disturbed and
unpredictable environments on the
planet.

170
00:22:05,720 --> 00:22:08,760
Because crocs need so little
to survive,

171
00:22:08,760 --> 00:22:12,600
they're able to maintain breeding
populations

172
00:22:12,600 --> 00:22:16,440
in places too poor for similar sized
fuel-hungry mammals.

173
00:22:17,320 --> 00:22:23,160
Crocodilians also have a mechanism
that helps them recover
from setbacks fast.

174
00:22:23,160 --> 00:22:26,520
When numbers are low, a higher
percentage of females reproduce

175
00:22:26,520 --> 00:22:28,480
and they do it more often.

176
00:22:31,080 --> 00:22:37,440
In Africa, a female Nile crocodile
is laying a batch of up to 60 eggs.

177
00:22:44,320 --> 00:22:47,840
She's dug a shallow scrape
along the riverbank

178
00:22:47,840 --> 00:22:53,720
and this soft, sandy soil will be
a natural incubator for her eggs.

179
00:22:53,720 --> 00:22:57,040
For seven weeks, she'll
guard them against predators,

180
00:22:57,040 --> 00:23:02,240
but her babies' lives will also
depend on what happens inside the
nest.

181
00:23:02,240 --> 00:23:06,240
They'll need a fairly stable
temperature if they are to develop
properly.

182
00:23:11,400 --> 00:23:15,080
Across the world,
in the Florida Everglades,

183
00:23:15,080 --> 00:23:20,160
another crocodilian mother lays the
foundations of the next generation.

184
00:23:20,160 --> 00:23:24,760
She's built a mound of dirt and
vegetation to incubate her eggs,

185
00:23:24,760 --> 00:23:28,000
a clutch of
baby North American alligators.

186
00:23:30,360 --> 00:23:35,920
Each egg contains enough food
to take the baby through
its whole development,

187
00:23:35,920 --> 00:23:39,360
but each new life depends
on more than just this.

188
00:23:42,360 --> 00:23:49,320
The young gators will only survive
if they're incubated between
26 and 35 degrees centigrade.

189
00:23:49,320 --> 00:23:54,760
Within this range,
specific temperatures will
determine their sex -

190
00:23:54,760 --> 00:23:59,520
those in the warmer eggs
will become male, and those in the
cooler eggs, female.

191
00:23:59,520 --> 00:24:03,080
Temperature will also determine
their rate of growth and help set

192
00:24:03,080 --> 00:24:09,040
the idling speed or metabolic rate
of their cold-blooded body engine.

193
00:24:11,880 --> 00:24:14,800
Hatchlings that develop
at the warmer end of the range

194
00:24:14,800 --> 00:24:20,160
will have a slightly higher metabolic
rate than siblings incubated at the
cooler end.

195
00:24:22,280 --> 00:24:28,000
They'll grow faster and will
have a head start in a warmer
environment with plenty of food.

196
00:24:28,000 --> 00:24:30,040
But in cooler conditions,

197
00:24:30,040 --> 00:24:36,240
the advantage will shift to
hatchlings incubated at cooler
temperatures.

198
00:24:41,560 --> 00:24:47,120
The newly-emerged baby alligators
call to their mother
from inside the nest.

199
00:25:05,800 --> 00:25:13,160
She's an attentive parent
and jaws that can crush bones gently
carry the babies down to water.

200
00:25:18,600 --> 00:25:24,280
The alligator hatchlings stay near
their mother for several months and
she'll do her best to protect them.

201
00:25:24,280 --> 00:25:28,520
This kind of care is unique
amongst reptiles.

202
00:25:34,640 --> 00:25:38,480
A crocodilian mother
has no way of feeding her young,

203
00:25:38,480 --> 00:25:42,000
so they must learn how to feed
themselves right from the start.

204
00:25:45,360 --> 00:25:51,640
It's a tough world, and even their
own kind may not always be on their
side.

205
00:25:51,640 --> 00:25:55,280
But Nile crocodile hatchlings,
barely out of the egg,

206
00:25:55,280 --> 00:25:58,600
already show all
the killer instincts of an adult.

207
00:26:03,000 --> 00:26:06,520
It's another key
to crocodilian success.

208
00:26:44,960 --> 00:26:51,680
Whatever the environment,
it seems that some of King Croc's
offspring will always survive.

209
00:27:01,040 --> 00:27:06,240
So the crocodilians' unique survival
kit has served them well in nature,

210
00:27:06,240 --> 00:27:09,800
but what about the man-made world?

211
00:27:09,800 --> 00:27:14,320
We're probably the greatest threat
they've ever had to face.

212
00:27:16,640 --> 00:27:20,680
We've polluted their homes,
slaughtered them in massive numbers,

213
00:27:23,440 --> 00:27:27,000
built our cities
on their ancestral lands.

214
00:27:31,520 --> 00:27:35,960
We've pushed some of their kind
to the very edge of survival.

215
00:27:41,320 --> 00:27:47,800
In the wild world, it would be
far too dangerous for people and
crocodilians to get this close.

216
00:27:51,760 --> 00:27:57,040
But there are places where crocs and
people are learning to share space.

217
00:27:57,040 --> 00:28:02,560
With a little help from us,
even the more vulnerable crocodilians
may be able to stage a comeback.

218
00:28:05,040 --> 00:28:07,760
Crocodilians have proved they're
tough,

219
00:28:07,760 --> 00:28:12,760
and truth is, some will probably
still be here long after we've gone.

220
00:28:19,040 --> 00:28:24,680
Long may King Croc,
supreme survivor, reign.

221
00:28:45,600 --> 00:28:47,760
Email us at subtitling@bbc.co.uk