0:00:02 > 0:00:04My name's Steve Backshall.
0:00:04 > 0:00:05Whoo!
0:00:05 > 0:00:10And this is my search for the Deadly 60.
0:00:10 > 0:00:12That's not just animals that are deadly to me,
0:00:12 > 0:00:15but animals that are deadly in their own world.
0:00:17 > 0:00:19My crew and I are travelling the planet.
0:00:19 > 0:00:21And you're coming with me.
0:00:21 > 0:00:22Every step of the way.
0:00:27 > 0:00:29'Deadly!'
0:00:29 > 0:00:32This time, the crew and I are back in Mexico.
0:00:32 > 0:00:36Situated between the southern United States and South America.
0:00:36 > 0:00:39It's a destination that's been good to us in the past,
0:00:39 > 0:00:42but this time, we're hoping to go even deeper,
0:00:42 > 0:00:47to prove to you there are deadly demons, even in this paradise.
0:00:47 > 0:00:50We're going to be diving to the depths of the ocean in search
0:00:50 > 0:00:54of an encounter with a versatile master shark.
0:00:54 > 0:00:58And setting up to witness an astonishing gathering of predators.
0:00:58 > 0:01:02But first, we're heading to a freshwater lagoon
0:01:02 > 0:01:04to look for a particularly Mexican reptile.
0:01:09 > 0:01:11It's the Morelet's crocodile,
0:01:11 > 0:01:15one of the most beautiful, yet most threatened of all crocodiles.
0:01:15 > 0:01:20We're joining a group of scientists who are studying these rare beasts,
0:01:20 > 0:01:23and we're hoping to help them catch one.
0:01:23 > 0:01:28They're most active after dark - the best time to go looking for them.
0:01:32 > 0:01:35While crocodiles can be incredibly tricky to find during the day,
0:01:35 > 0:01:39at night, we have one thing that's very much on our side - eyeshine.
0:01:39 > 0:01:42That's what Marco's looking for now.
0:01:42 > 0:01:44There's a reflective layer of cells at the back of the eye
0:01:44 > 0:01:46and when a torch is shone at them,
0:01:46 > 0:01:50they reflect back in a glowing, red-hot blaze.
0:01:50 > 0:01:53It really gives away the position of the crocodile.
0:01:54 > 0:01:58Both Marco and I take turns with the spotlight.
0:02:00 > 0:02:03Once you spot them, they can be hard to keep track of.
0:02:03 > 0:02:06There it is again. Just there, look.
0:02:07 > 0:02:09There. Behind us.
0:02:12 > 0:02:13Can you hold this?
0:02:18 > 0:02:20Aye!
0:02:22 > 0:02:24Just got very soggy and very smelly...
0:02:26 > 0:02:28..and failed to catch it.
0:02:39 > 0:02:41Oh!
0:02:41 > 0:02:43OK.
0:02:43 > 0:02:44YELPING
0:02:44 > 0:02:47Well, it's not quite what we were hoping for,
0:02:47 > 0:02:52but it is our first Morelet's crocodile.
0:02:53 > 0:02:56And as soon as it was caught...
0:02:57 > 0:03:00..it let rip with what I think
0:03:00 > 0:03:02is one of the cutest sounds in the animal kingdom.
0:03:02 > 0:03:04Listen to this.
0:03:04 > 0:03:06YELPING
0:03:09 > 0:03:12That is the juvenile alarm call,
0:03:12 > 0:03:15which is common to all crocodiles,
0:03:15 > 0:03:20and is usually used to try and attract the attention of the mother.
0:03:20 > 0:03:24Um...we have seen, in this area here,
0:03:24 > 0:03:28a crocodile that is large enough to be a mature female
0:03:28 > 0:03:30and could well be Mum to this one,
0:03:30 > 0:03:34so I should probably get back in the boat. Step back a sec, Johnny.
0:03:38 > 0:03:40Isn't that beautiful?
0:03:40 > 0:03:43Very cute.
0:03:43 > 0:03:46But much, much too small for our needs.
0:03:47 > 0:03:50So, after getting into some dry clothes,
0:03:50 > 0:03:55we continued our mission for a slightly bigger croc.
0:03:58 > 0:04:00There we go.
0:04:00 > 0:04:04Marco's given the signal that he's spotted something.
0:04:04 > 0:04:06It appears it's dived.
0:04:15 > 0:04:16It's a good-sized animal.
0:04:16 > 0:04:20Probably at least a metre-and-a-half long.
0:04:20 > 0:04:23But it moved off at quite a pace in that direction.
0:04:24 > 0:04:28Crocodiles are capable of staying underwater for long amounts of time
0:04:28 > 0:04:32when they're waiting in ambush for prey. Several hours is not unusual.
0:04:32 > 0:04:36They slow their heartbeat right down, they don't use oxygen.
0:04:36 > 0:04:39But when they're swimming fast, they're using up a lot of oxygen,
0:04:39 > 0:04:42- so they can't stay down for very long.- We've got him.
0:04:42 > 0:04:47This croc hasn't been to the surface for a couple of minutes now
0:04:47 > 0:04:49and it's been swimming almost that entire time,
0:04:49 > 0:04:52so it will be up to breathe very soon.
0:05:15 > 0:05:18After a good ten minutes...
0:05:18 > 0:05:21of chasing and evading us extraordinarily well,
0:05:21 > 0:05:25we've managed to catch our Morelet's crocodile.
0:05:26 > 0:05:29We need to make sure the crocodile's jaws are secured
0:05:29 > 0:05:32while the scientists gather data
0:05:32 > 0:05:34essential for the protection of this wonder.
0:05:34 > 0:05:38I know this probably all seems quite harsh on the animal,
0:05:38 > 0:05:42but crocodiles have these scales here behind their head,
0:05:42 > 0:05:46they're called scoots, and they're unbelievably strong.
0:05:46 > 0:05:49They're like armour plating and protect the crocodile,
0:05:49 > 0:05:51so this won't have done it any harm.
0:05:51 > 0:05:54I've handled a lot of crocodiles around the world,
0:05:54 > 0:05:56but I've never seen one that has
0:05:56 > 0:05:59this incredibly silky, almost velvety skin.
0:05:59 > 0:06:01It is simply glorious.
0:06:01 > 0:06:03It has so many of the attributes
0:06:03 > 0:06:06that you'd expect from a crocodile of this kind of size.
0:06:06 > 0:06:11It has this broad, paddle-shaped tail with thick muscles at the back.
0:06:11 > 0:06:14But it's not just the tail that does the work.
0:06:14 > 0:06:18The rear feet are also slightly webbed.
0:06:18 > 0:06:20Although generally, when it's swimming,
0:06:20 > 0:06:23these will fold back along the side of the body,
0:06:23 > 0:06:26making it streamlined in the water, it can use these
0:06:26 > 0:06:28to power and propel itself.
0:06:28 > 0:06:31It will actually run, literally run along the bottom,
0:06:31 > 0:06:33which gives it another means of locomotion.
0:06:33 > 0:06:37It can make the most of any opportunity that comes its way,
0:06:37 > 0:06:40and that could be anything from fish, from invertebrates,
0:06:40 > 0:06:44up to birds and even mammals that come down alongside the shore.
0:06:44 > 0:06:48It will get a hold of them in much the same way it's been evading us -
0:06:48 > 0:06:51by staying underwater, by staying camouflaged
0:06:51 > 0:06:55and at the last minute, attacking with enormous bursts of pace.
0:06:55 > 0:06:59I could literally talk about this animal all night long,
0:06:59 > 0:07:01but the guys have got some science to do.
0:07:01 > 0:07:05It's really important to keep tabs on how the crocodiles are doing.
0:07:05 > 0:07:06I'll let them do their work
0:07:06 > 0:07:09then return this magnificent animal to the water.
0:07:09 > 0:07:12This work is helping to save an animal
0:07:12 > 0:07:14that would otherwise probably have gone extinct.
0:07:14 > 0:07:16A nearby reptile rescue centre
0:07:16 > 0:07:19is also battling to save Morelet's crocs.
0:07:23 > 0:07:27Behind me is an enclosure filled with rescued Morelet's crocodiles.
0:07:27 > 0:07:31Most of these have turned up in someone's backyard or swimming pool
0:07:31 > 0:07:34and been brought here so that they'll be safe.
0:07:34 > 0:07:37This...is a pressure gauge.
0:07:37 > 0:07:41The way this works is that we have a kind of jelly inside here
0:07:41 > 0:07:43which is under pressure,
0:07:43 > 0:07:46and when this is squeezed, or in this case bitten,
0:07:46 > 0:07:49the exact force is going to come up on this gauge here.
0:07:49 > 0:07:52And it'll tell us how powerful the bite is of the animal.
0:07:52 > 0:07:56Crocodiles are known for having the most powerful bites of any animal.
0:07:56 > 0:07:59Even though the Morelet's is not a massive crocodile,
0:07:59 > 0:08:01I'm expecting something impressive.
0:08:04 > 0:08:06So what we need to do now
0:08:06 > 0:08:11is to get one of these crocodiles into a corner
0:08:11 > 0:08:14so that it can't make its way into the water.
0:08:18 > 0:08:20OK. We've decided on this one here
0:08:20 > 0:08:23that we're going to try and get into that corner.
0:08:23 > 0:08:25I need to block his escape route.
0:08:27 > 0:08:28Whoo!
0:08:32 > 0:08:35- Well, that didn't work very well! - HE LAUGHS
0:08:35 > 0:08:40These animals really aren't naturally aggressive towards people.
0:08:40 > 0:08:43In fact, their first instinct is to try and get away.
0:08:43 > 0:08:46That doesn't mean we shouldn't have a healthy respect for them
0:08:46 > 0:08:50and be very careful where we're putting our feet.
0:08:50 > 0:08:52Watch this one.
0:08:54 > 0:08:56Ooo!
0:08:56 > 0:09:00That was just a little snap and that raised about 500lb.
0:09:08 > 0:09:13That was pretty impressive. That was 600lb per square inch.
0:09:15 > 0:09:18And that is not a bite
0:09:18 > 0:09:22that's actually being used to tear apart prey.
0:09:23 > 0:09:27That's purely a show of teeth to try and scare us off. It shows...
0:09:27 > 0:09:29the formidable power
0:09:29 > 0:09:32in the muscles that drive that jaw.
0:09:35 > 0:09:40You can see they do move very quickly over short distances.
0:09:40 > 0:09:43And in the swampy habitats that this animal lives in,
0:09:43 > 0:09:46this is really, really important.
0:09:50 > 0:09:52Whoa! OK.
0:09:53 > 0:09:57Well...he's punctured my bite gauge.
0:09:57 > 0:09:59HE LAUGHS
0:09:59 > 0:10:01That is remarkable.
0:10:01 > 0:10:07A fantastic bite...from a two-and-a-half metre long croc.
0:10:08 > 0:10:12And that's 800lb per square inch.
0:10:12 > 0:10:14Very, very impressive.
0:10:16 > 0:10:19The marvellous Mexican Morelet's crocodile.
0:10:19 > 0:10:22They're pretty snappy, but they're certainly not a man-eater.
0:10:22 > 0:10:25They are, though, an absolute wonder of the swamps.
0:10:25 > 0:10:29And for that reason, I reckon they have to go on the Deadly 60.
0:10:32 > 0:10:35Dynamic jaw muscles create a formidable bite force.
0:10:35 > 0:10:39With tough, protective scales that act like armour plating,
0:10:39 > 0:10:41these stealthy, camouflaged crocodiles
0:10:41 > 0:10:43ambush their unsuspecting prey.
0:10:43 > 0:10:47This Mexican marvel is going on my list.
0:10:47 > 0:10:49'Deadly.'
0:10:49 > 0:10:51It's all been a bit tough so far,
0:10:51 > 0:10:55so I'm breaking out the sunscreen and heading to the beach.
0:10:55 > 0:10:57This part of Mexico's east coast
0:10:57 > 0:11:00has some of the biggest tourist destinations,
0:11:00 > 0:11:02biggest resorts in the whole world.
0:11:02 > 0:11:05Every day, thousands of people use these seas,
0:11:05 > 0:11:07but if you head out for five minutes,
0:11:07 > 0:11:10there is an unbelievable concentration
0:11:10 > 0:11:12of one of the most feared animals on Earth.
0:11:12 > 0:11:15This is a creature that has a reputation
0:11:15 > 0:11:17for being a ruthless man-eater.
0:11:17 > 0:11:20So, as appealing as the sand and the sea is right here,
0:11:20 > 0:11:24it's going to be much more exciting out there.
0:11:24 > 0:11:27It's a shark that just looks like trouble.
0:11:27 > 0:11:30The bull shark. They're stocky, pugnacious predators.
0:11:30 > 0:11:34Named for their bullish appearance, attitude
0:11:34 > 0:11:37and habit of head-butting anything in their path.
0:11:37 > 0:11:41Bull sharks have the worst reputation of all sharks.
0:11:41 > 0:11:46And are probably more feared than tiger sharks, and even great whites.
0:11:48 > 0:11:53They are man-eaters, mostly because they're tremendously adaptable.
0:11:53 > 0:11:56They can swim thousands of miles up freshwater rivers
0:11:56 > 0:12:02and often hunt in murky waters where humans can be mistaken for prey.
0:12:10 > 0:12:13In tropical and subtropical waters like these,
0:12:13 > 0:12:16the bull shark absolutely rules.
0:12:16 > 0:12:19As an adult, it has no natural predators whatsoever.
0:12:19 > 0:12:22We're heading down into the kingdom of the bull shark.
0:12:22 > 0:12:24This is a place where humans like us
0:12:24 > 0:12:26seem impossibly cumbersome and fragile.
0:12:26 > 0:12:30So there really are very few more exciting wildlife encounters
0:12:30 > 0:12:33than the one we're about to experience. I hope.
0:12:33 > 0:12:36Everything now is down to what the bull shark wants,
0:12:36 > 0:12:39so we're just going to keep our eyes open, watch each other's backs
0:12:39 > 0:12:42and just hope that they're interested in us.
0:12:42 > 0:12:45- OK, guys, let's do it.- OK.- OK.
0:12:45 > 0:12:47Bull sharks can be dangerous,
0:12:47 > 0:12:50so Simon the cameraman and I will have another diver
0:12:50 > 0:12:53keeping an eye on us, just in case.
0:12:53 > 0:12:58But the danger sharks pose to people is massively sensationalised.
0:12:58 > 0:13:02In clear waters, where the sharks can see exactly what we are,
0:13:02 > 0:13:04they're highly unlikely to attack.
0:13:04 > 0:13:07That doesn't mean my heart isn't racing as we descend.
0:13:07 > 0:13:10I know sharks are out there and their senses are so keen,
0:13:10 > 0:13:13they'll have perceived us the second we hit the water.
0:13:15 > 0:13:19These intriguing fish
0:13:19 > 0:13:22are called remoras, or sucker fish.
0:13:22 > 0:13:25You can probably see the strange shapes on top of its head.
0:13:25 > 0:13:29They're sucker cups, used to attach it to a larger fish
0:13:29 > 0:13:33so they can live off the scraps that things like sharks leave behind.
0:13:35 > 0:13:40So if you see one of these, there's going to be a shark around.
0:13:41 > 0:13:44And our first bull shark is coming towards us right now.
0:13:44 > 0:13:46Look at this!
0:13:49 > 0:13:51Right, we've got two.
0:13:51 > 0:13:57And that one there has an enormous amount of fusiliers.
0:13:57 > 0:14:00They're using the sandpaper-like skin of the shark
0:14:00 > 0:14:03to rub their own bodies on...
0:14:05 > 0:14:07..to remove parasites from their skin.
0:14:10 > 0:14:14The bull shark has all of the senses you'd expect from a shark.
0:14:14 > 0:14:17They have the ability to pick up electrical signals
0:14:17 > 0:14:22from the moving muscles of their prey and, also, to sense vibration.
0:14:25 > 0:14:30They can glide along with just a lazy movement of their tail.
0:14:30 > 0:14:33But don't be fooled by that.
0:14:33 > 0:14:37They can put on explosive bursts of pace when they're hunting.
0:14:39 > 0:14:45Bull sharks are real opportunists, eating a massive array of food.
0:14:45 > 0:14:48Most of the time, that's fish, but they will feed
0:14:48 > 0:14:53on other sharks, mammals, birds at the surface and even turtles.
0:14:54 > 0:14:58Just heading along the bottom towards us is a loggerhead turtle.
0:15:00 > 0:15:02Look at the size of its head.
0:15:04 > 0:15:08Right now, I have to say, I wouldn't want to be this turtle.
0:15:08 > 0:15:12Surrounded by animals that could well want to try and eat you.
0:15:14 > 0:15:17It's a very, very beautiful creature.
0:15:17 > 0:15:19They do need to breathe air,
0:15:19 > 0:15:23so it will have to return to the surface at some point.
0:15:23 > 0:15:27At which point, it's going to become very, very vulnerable.
0:15:28 > 0:15:30Isn't it wonderful!
0:15:30 > 0:15:35As the sun sets above us, the sharks' body language changes.
0:15:35 > 0:15:40Their movements are less languid and lazy, more mean and menacing.
0:15:40 > 0:15:45There must be 10 or 15 of them around us at the moment,
0:15:45 > 0:15:48all circling us with real intent.
0:15:49 > 0:15:51Look at these three!
0:15:56 > 0:15:58Such dramatic animals.
0:16:01 > 0:16:02Whoa!
0:16:02 > 0:16:05There's no doubt, approaching dusk,
0:16:05 > 0:16:09these animals have a totally different attitude about them.
0:16:09 > 0:16:15It's clear that now they're ready... to start hunting.
0:16:15 > 0:16:17The current's really quite strong.
0:16:17 > 0:16:21We're having to hang onto the bottom to avoid being dragged away.
0:16:21 > 0:16:24Just another thing you really don't want to be thinking about
0:16:24 > 0:16:26when you're surrounded by this lot.
0:16:26 > 0:16:30There's something about them now that's truly chilling.
0:16:30 > 0:16:33Their noses down, they seem twitchy, poised, ready to explode.
0:16:33 > 0:16:36I'm not so worried about the sharks I can see,
0:16:36 > 0:16:38it's the ones that I can't.
0:16:43 > 0:16:45This is genuinely one of those moments
0:16:45 > 0:16:49when you wish you had eyes in the back of your head.
0:16:49 > 0:16:52I keep catching something in the edge of my view
0:16:52 > 0:16:56and it's a shark and they're coming right in behind you. Like that.
0:16:58 > 0:17:02Wow! They are some of the most menacing of all sharks.
0:17:09 > 0:17:13It feels like it might be time to head for the surface.
0:17:15 > 0:17:19It is kind of incredible that we can be swimming in these seas,
0:17:19 > 0:17:25surrounded by bull sharks, and just a few minutes in that direction,
0:17:25 > 0:17:29there are tourists splashing around happily on the beaches.
0:17:29 > 0:17:33Just goes to show these animals are actually really acutely aware
0:17:33 > 0:17:38of everything in their environment. They know we're not food.
0:17:39 > 0:17:42Otherwise, you wouldn't stand a chance down here.
0:17:45 > 0:17:49Bull sharks move deceptively carefully and slowly,
0:17:49 > 0:17:52but they can put on a real burst of pace if they have to.
0:17:52 > 0:17:57They're very adaptable. They can hunt here in these coastal waters
0:17:57 > 0:18:00or they can move right up inland on freshwater rivers.
0:18:00 > 0:18:03This is an unbelievable predator.
0:18:03 > 0:18:06An animal that surely has to go on the Deadly 60.
0:18:06 > 0:18:09Bull sharks, Deadly!
0:18:11 > 0:18:14With the ability to swim in both salt and fresh water,
0:18:14 > 0:18:18they can pick up electrical signals and vibrations from their prey
0:18:18 > 0:18:23and they're none too fussy about what they eat.
0:18:23 > 0:18:27These masters of adapting are remarkable on the inside and out.
0:18:27 > 0:18:29'Deadly!'
0:18:31 > 0:18:34For our last contender, we're doing something different.
0:18:34 > 0:18:39We're not looking for an animal, but a phenomenon.
0:18:39 > 0:18:44We'll look at one of the greatest gatherings of predators on Earth.
0:18:46 > 0:18:48Oh! Whoa!
0:18:48 > 0:18:51Do you know what, I smelt it before I saw it.
0:18:51 > 0:18:54Just getting to the edge...
0:18:54 > 0:18:59you just get hit by a whiff of ammonia
0:18:59 > 0:19:03and centuries-old bat droppings.
0:19:03 > 0:19:09Below us is a mighty cavern, a sinkhole.
0:19:09 > 0:19:12What will have happened here is a big cave,
0:19:12 > 0:19:14the roof will have collapsed in
0:19:14 > 0:19:17and now it's just a hole going directly down,
0:19:17 > 0:19:19straight into the Earth.
0:19:19 > 0:19:25And down there are hundreds of thousands, millions of bats.
0:19:25 > 0:19:29And those millions of mouths need feeding.
0:19:29 > 0:19:31Soon, they'll explode from the cave
0:19:31 > 0:19:34in a gargantuan swarm too vast to appreciate.
0:19:34 > 0:19:36In order to see what the swarm's made up of,
0:19:36 > 0:19:40we're working with some scientists studying the bats.
0:19:40 > 0:19:43They're erecting nets to catch the bats without harming them
0:19:43 > 0:19:46so we'll be able to see their attributes up close.
0:19:46 > 0:19:48Local people call this the bat volcano.
0:19:48 > 0:19:52And the volcano is about to erupt.
0:19:53 > 0:19:57We haven't seen any bats yet, but you can hear them.
0:19:57 > 0:20:00There's an incredible range of sounds coming up through the cave
0:20:00 > 0:20:04and the sinkhole itself is almost functioning like a loudspeaker,
0:20:04 > 0:20:06amplifying those sounds.
0:20:06 > 0:20:11Then the source of the sound begins to spew out of the cave beneath.
0:20:11 > 0:20:14I cannot believe how quickly that started!
0:20:14 > 0:20:17From absolutely nothing at all,
0:20:17 > 0:20:21a whirlwind of bats has just erupted
0:20:21 > 0:20:25and started forming a vortex circling higher.
0:20:25 > 0:20:28And...they're level with me.
0:20:29 > 0:20:33And pretty soon, they're going to head out into the forest.
0:20:33 > 0:20:36One of the greatest hunting machines on Earth.
0:20:38 > 0:20:41Any insects around here are in big trouble.
0:20:41 > 0:20:44BUZZING
0:20:44 > 0:20:48The sound of their wings is just phenomenal!
0:20:48 > 0:20:50I actually have to raise my voice
0:20:50 > 0:20:53to be heard above the sound of these bats' wings.
0:20:53 > 0:20:57And there is a wind being driven out from the hole...
0:20:59 > 0:21:01..just purely from their flapping wings.
0:21:01 > 0:21:05There are nine different species of bats living inside this cave.
0:21:05 > 0:21:07One of them feeds on nectar,
0:21:07 > 0:21:10the rest are all insect-feeding bats.
0:21:10 > 0:21:14And...this is one of the greatest aggregations,
0:21:14 > 0:21:16that is collections of predators,
0:21:16 > 0:21:20that you will see on the whole planet.
0:21:20 > 0:21:23This is one of the greatest spectacles I have ever witnessed.
0:21:23 > 0:21:26From nothing to an eruption of bats.
0:21:26 > 0:21:28This really is a volcano of bats.
0:21:30 > 0:21:32That is extraordinary!
0:21:32 > 0:21:35To see them begin their nightly pilgrimage,
0:21:35 > 0:21:38we scramble to a higher viewpoint above the sinkhole.
0:21:40 > 0:21:42We just quickly ran up above the sinkhole,
0:21:42 > 0:21:46just to catch the last few rays of sunshine
0:21:46 > 0:21:49illuminating this cloud of bats,
0:21:49 > 0:21:52just heading out almost like tendrils of smoke
0:21:52 > 0:21:54over the top of the forest.
0:21:54 > 0:21:59It really is one of the most beautiful sights I've ever seen.
0:21:59 > 0:22:02Every single one of the bats, their wings are backlit by the sunshine,
0:22:02 > 0:22:06so you can see these tiny little phantoms glowing orange
0:22:06 > 0:22:09as they hover above the forest.
0:22:09 > 0:22:13And look at that now! Just heading across the skyline.
0:22:13 > 0:22:18In just great, long, smoky tubes.
0:22:23 > 0:22:26It may seem crazy to be looking at something so exquisite
0:22:26 > 0:22:29and suggesting it as something that should go on the Deadly 60,
0:22:29 > 0:22:31but actually, in terms of scale,
0:22:31 > 0:22:35we will never feature anything that is such an epic display
0:22:35 > 0:22:38of predatory behaviour as this ever on the series.
0:22:38 > 0:22:41I mean, there's anywhere up to two-and-a-half million bats
0:22:41 > 0:22:42coming out of these caves.
0:22:42 > 0:22:47Each could eat half its bodyweight, perhaps even more, in insects
0:22:47 > 0:22:49every single night.
0:22:49 > 0:22:51There is no other predator that could do that.
0:22:51 > 0:22:54There's no lion that can eat its own bodyweight in gazelle
0:22:54 > 0:22:57or orca that can eat its own bodyweight in sea lion.
0:22:57 > 0:23:00What these bats are doing is truly extraordinary,
0:23:00 > 0:23:03and they're doing it on a massive, massive scale.
0:23:07 > 0:23:12It's a sight that you can see in very few places in the world.
0:23:12 > 0:23:15In magnitude, this is one of nature's true miracles.
0:23:15 > 0:23:19But take a closer look and it's perhaps even more miraculous.
0:23:23 > 0:23:26Insect-eating bats perceive their world using echolocation.
0:23:26 > 0:23:29This involves sending out high-frequency clicks
0:23:29 > 0:23:33from deep in their throat which most of their prey won't detect.
0:23:33 > 0:23:35These sounds act as a searchlight,
0:23:35 > 0:23:39scanning an area and echoing back as they bounce off objects.
0:23:39 > 0:23:42As they get closer to their prey, the time between clicks shortens,
0:23:42 > 0:23:46allowing them to pinpoint things with remarkable precision.
0:23:46 > 0:23:49The returning echoes are received in their large ears
0:23:49 > 0:23:51and give the bats a three-dimensional picture
0:23:51 > 0:23:53of everything in the vicinity.
0:23:53 > 0:23:57In the darkness, they discriminate between echoes from prey
0:23:57 > 0:24:00and echoes from things like twigs and leaves.
0:24:00 > 0:24:04It's one of the most complex predator-prey interactions.
0:24:09 > 0:24:10The sun has completely set,
0:24:10 > 0:24:13yet the bats still pour out unabated from the cavern.
0:24:13 > 0:24:17Let's take a closer look at the players in our super swarm.
0:24:17 > 0:24:20After rodents, the bats are the most bio-diverse
0:24:20 > 0:24:22group of mammals on the planet.
0:24:22 > 0:24:25There's well over 1,000 species and I don't know all of them.
0:24:25 > 0:24:28But the scientists thankfully do seem to know them all
0:24:28 > 0:24:31and they've reliably informed me
0:24:31 > 0:24:34that this one here is called Davy's naked-backed bat.
0:24:34 > 0:24:37And you can see why. Look at this.
0:24:37 > 0:24:40It's all furry down to about here,
0:24:40 > 0:24:44and then the whole of the back is just completely naked of fur.
0:24:44 > 0:24:47- It looks like it's been shaved. - HE LAUGHS
0:24:47 > 0:24:51This is a hairy-legged myotis bat.
0:24:51 > 0:24:57And it just looks like a tiny little miniature teddy bear with wings.
0:24:57 > 0:25:01It is just incredible that even at this tiny size,
0:25:01 > 0:25:04this animal has probably the most sophisticated
0:25:04 > 0:25:07prey-detection system of any creature on Earth.
0:25:07 > 0:25:10This is the ghost-faced bat.
0:25:10 > 0:25:13And I have to admit, even to me,
0:25:13 > 0:25:16that is a face that's pretty repulsive.
0:25:16 > 0:25:19Now, it's centred around these whacking great big ears,
0:25:19 > 0:25:22and you can see that actually what these do
0:25:22 > 0:25:25is almost turn the entire head into a satellite dish.
0:25:25 > 0:25:28This is called the common moustached bat.
0:25:28 > 0:25:32You can see why, because lying along the length of the upper lip
0:25:32 > 0:25:36is what looks like some kind of crazy moustache.
0:25:36 > 0:25:38But that's not what's interesting to me.
0:25:38 > 0:25:42I think the most remarkable thing is that between the feet here...
0:25:42 > 0:25:45is this membrane.
0:25:45 > 0:25:48Tail runs down the middle of it
0:25:48 > 0:25:51and it acts almost like a baseball catcher's net.
0:25:52 > 0:25:55Many species of bat have this tail membrane.
0:25:55 > 0:25:58They use it to catch insects that are flying by.
0:25:58 > 0:26:01They scoop up their prey, transfer it to their mouths
0:26:01 > 0:26:03and consume it whilst still in flight.
0:26:05 > 0:26:08The scientists have done their work on this one. He can fly free.
0:26:09 > 0:26:12Fantastic!
0:26:12 > 0:26:14This is the bat I was hoping to find.
0:26:14 > 0:26:17It's called the Mexican free-tailed bat.
0:26:17 > 0:26:20And the reason for that is you can see
0:26:20 > 0:26:24the tail here is actually free of the wing membrane.
0:26:24 > 0:26:29Mexican free-tailed bats roost in truly mammoth colonies.
0:26:29 > 0:26:32Their efficiency is absolutely extraordinary.
0:26:32 > 0:26:35He has, though, got a fairly fearsome set of gnashers.
0:26:35 > 0:26:40The teeth inside there are genuinely needle-sharp.
0:26:40 > 0:26:44Capable of munching through the tough exoskeleton of a flying beetle
0:26:44 > 0:26:47or munching down a moth that could be the same size as this bat.
0:26:47 > 0:26:51It is an absolute wonder.
0:26:51 > 0:26:53In fact, every bat here is wonderful.
0:26:53 > 0:26:57And they're all truly worth their weight in insects.
0:26:58 > 0:27:00So really, I know it's weird,
0:27:00 > 0:27:02but I'm going to put all of the bats from the bat volcano
0:27:02 > 0:27:05onto the Deadly 60.
0:27:07 > 0:27:09With a complex hunting technique
0:27:09 > 0:27:11enabling them to locate prey in total darkness,
0:27:11 > 0:27:15they catch moving insects on the wing with superb agility.
0:27:15 > 0:27:20Collectively consuming more than half a tonne of insects every night.
0:27:20 > 0:27:23This mass of munching mammals is definitely...
0:27:23 > 0:27:25'Deadly!'
0:27:25 > 0:27:31Join me next time as I continue my search for the Deadly 60.
0:27:31 > 0:27:33- I can see it! I can see it! - Go, go, go, go, go!
0:27:37 > 0:27:39Subtitles by Red Bee Media Ltd