0:00:04 > 0:00:06Planet Earth.
0:00:06 > 0:00:08Millions of species.
0:00:11 > 0:00:13But a few are special.
0:00:16 > 0:00:18Born to thrive.
0:00:26 > 0:00:30The key to their success lies in their opportunism.
0:00:32 > 0:00:36For others, it's down to their ability to collaborate
0:00:36 > 0:00:39and, for some, it's all about
0:00:39 > 0:00:42surviving where others can't.
0:00:45 > 0:00:47So, what is their secret?
0:00:50 > 0:00:53In this series, we'll delve deep beneath the skin to reveal
0:00:53 > 0:00:57the unique features that set some species apart.
0:01:02 > 0:01:04New behaviour and the very
0:01:04 > 0:01:08latest scientific discoveries will offer fresh insight into
0:01:08 > 0:01:11the wonder of animals.
0:01:31 > 0:01:33New Zealand...
0:01:35 > 0:01:39..over 1,000 miles from the nearest continent.
0:01:43 > 0:01:47Every mammal on these islands was brought here by humans.
0:01:53 > 0:01:57All, that is, except one.
0:02:05 > 0:02:06The bat.
0:02:12 > 0:02:17These remarkable animals have colonised some of the remotest
0:02:17 > 0:02:19places on our planet...
0:02:25 > 0:02:30..becoming one of the most widespread of all mammals on Earth.
0:02:34 > 0:02:38And there are three key ingredients to their success.
0:02:47 > 0:02:50First, an incredible anatomy.
0:02:50 > 0:02:54One which has enabled them not to just take to the air...
0:02:56 > 0:03:00..but to master it like no other animal can.
0:03:06 > 0:03:11Second, a raft of unrivalled senses
0:03:11 > 0:03:15that's allowed them to feed in some extraordinary ways.
0:03:24 > 0:03:29And finally, their sophisticated physiology,
0:03:29 > 0:03:34which means that they've been able to survive
0:03:34 > 0:03:37in some of the most surprising places.
0:03:39 > 0:03:43In this episode, we will take a closer look at these three
0:03:43 > 0:03:51key factors to uncover the incredible abilities of bats.
0:04:05 > 0:04:09Having taken to the skies around 60 million years ago,
0:04:09 > 0:04:13bats are the only mammals that can truly fly.
0:04:18 > 0:04:22But the way their anatomy has evolved to do this is completely
0:04:22 > 0:04:25different to any other flying animal.
0:04:33 > 0:04:37Whereas birds' wings evolved by extending the forearms
0:04:37 > 0:04:41and shortening the fingers, bats' wings are different.
0:04:49 > 0:04:54The arms are still important, but it's the bones in the hand
0:04:54 > 0:04:57that offer additional dexterity.
0:05:00 > 0:05:05The thumbs became claws and the four, bony fingers
0:05:05 > 0:05:07on each hand have elongated.
0:05:08 > 0:05:12It's this that allows bats to change
0:05:12 > 0:05:14their wing shape in an instant.
0:05:18 > 0:05:22The result is an unprecedented manoeuvrability.
0:05:26 > 0:05:29They can make a 180-degree turn
0:05:29 > 0:05:33in less than half the length of their wing-span.
0:05:38 > 0:05:42And this wing pattern comes in all shapes and sizes.
0:05:48 > 0:05:51Short, wide wings are perfectly suited for hunting
0:05:51 > 0:05:54mobile prey in dense environments.
0:06:03 > 0:06:07While long, narrow wings of the larger bats, like flying foxes,
0:06:07 > 0:06:10help in long-distance flights...
0:06:14 > 0:06:18..allowing them to travel up to 40km in a single night.
0:06:26 > 0:06:30To fly such distances, it's important to minimise weight.
0:06:33 > 0:06:37So, a bat's wing bones are bound together by a super-thin,
0:06:37 > 0:06:39lightweight membrane.
0:06:41 > 0:06:44It's so thin that it can be susceptible to tearing.
0:06:51 > 0:06:53But bats have a solution.
0:06:56 > 0:07:01It's one of the fastest healing tissues of any mammal,
0:07:01 > 0:07:05repairing itself ten times quicker than human skin.
0:07:09 > 0:07:12Even a hole this size can be completely healed
0:07:12 > 0:07:13in just a few weeks.
0:07:17 > 0:07:21But although the surface of this membrane looks smooth,
0:07:21 > 0:07:26it's actually covered in thousands of tiny hairs.
0:07:31 > 0:07:34Almost invisible to the naked eye,
0:07:34 > 0:07:38they can be as short as a tenth of a millimetre
0:07:38 > 0:07:41and 12 times thinner than a human hair.
0:07:47 > 0:07:49But they're not here to keep the bats warm.
0:07:51 > 0:07:56At the base of each hair are minute sensory cells.
0:07:58 > 0:08:03These give the bats a detailed and instant airflow map during flight.
0:08:06 > 0:08:07The position of the hairs
0:08:07 > 0:08:12across the wing surface monitor the precise direction of air currents.
0:08:15 > 0:08:21Bats can then calculate when to accelerate and when to decelerate...
0:08:22 > 0:08:25..and also detect turbulence that might otherwise
0:08:25 > 0:08:26cause them to stall.
0:08:35 > 0:08:39This amazing anatomy from lightweight bones to
0:08:39 > 0:08:42super-thin, hair-covered membranes
0:08:42 > 0:08:45has enabled bats to conquer the skies.
0:08:53 > 0:08:58But although crucial to their ability to colonise the planet,
0:08:58 > 0:09:02this unique system of flying also presents bats
0:09:02 > 0:09:05with their single greatest challenge.
0:09:10 > 0:09:15In terms of energy, bat flight is incredibly expensive.
0:09:15 > 0:09:19When they're flying, they burn up twice as much energy per second as
0:09:19 > 0:09:23a similar sized mammal would if it were running.
0:09:27 > 0:09:30And some bat species have to
0:09:30 > 0:09:35beat their wings at 14 times a second just to stay airborne
0:09:35 > 0:09:38and this can drive their heart rate
0:09:38 > 0:09:43up to an astonishing 800 beats per minute!
0:09:47 > 0:09:53A single hour of flight can use up 10% of their total supply of energy.
0:09:53 > 0:09:55So, after a busy night's hunting,
0:09:55 > 0:09:58they're practically running on empty.
0:10:04 > 0:10:07The bats need to recover their energy
0:10:07 > 0:10:10and to do this they must feed.
0:10:10 > 0:10:13They've got to find the richest food available
0:10:13 > 0:10:16in the most efficient way possible.
0:10:16 > 0:10:20That's where their astounding senses come in.
0:10:28 > 0:10:33In temperate climates like the UK, the most energy-rich food source
0:10:33 > 0:10:35for bats is very small...
0:10:37 > 0:10:39..and always on the move.
0:10:47 > 0:10:49Like all insect-eating bats,
0:10:49 > 0:10:53the Natterer's uses echolocation to hunt its prey.
0:10:53 > 0:10:54BAT CHIRPS
0:11:04 > 0:11:08By emitting a series of high-pitched calls
0:11:08 > 0:11:11and interpreting what bounces back,
0:11:11 > 0:11:14it can pinpoint its prey's precise location.
0:11:16 > 0:11:20But the problem for most echolocating animals is that
0:11:20 > 0:11:24emitting these calls means using even more energy.
0:11:26 > 0:11:30But scientists have discovered that bats have evolved a solution.
0:11:36 > 0:11:40The muscles that move their wings are the same muscles that
0:11:40 > 0:11:42operate their lungs.
0:11:47 > 0:11:51So during flight, every breath
0:11:51 > 0:11:54coincides with every wing beat.
0:11:54 > 0:11:58They breathe in on the down stroke
0:11:58 > 0:12:00and out on the up stroke.
0:12:04 > 0:12:06So when the bat is breathing out...
0:12:08 > 0:12:12..it takes almost no extra energy to emit an
0:12:12 > 0:12:14echolocation pulse at the same time.
0:12:16 > 0:12:19A bat will only break this arrangement
0:12:19 > 0:12:22when it closes in on its target.
0:12:22 > 0:12:25Then it emits a frenzy of pulses...
0:12:25 > 0:12:27FAST CLICKING SOUND
0:12:29 > 0:12:33..to give it a much more detailed picture of its prey.
0:12:47 > 0:12:50This energy-saving technique
0:12:50 > 0:12:54is so effective that a single bat can stay airborne long enough
0:12:54 > 0:12:59to consume one third of its own body weight in insects every night.
0:13:02 > 0:13:06Hundreds in a single feeding session!
0:13:10 > 0:13:15In Belize, however, there's a bat that uses echolocation
0:13:15 > 0:13:19to get all of its energy in just one go.
0:13:21 > 0:13:26This is the greater bulldog bat and, rather than fly around
0:13:26 > 0:13:28all night looking for small prey,
0:13:28 > 0:13:32it targets a much bigger meal.
0:13:38 > 0:13:43It uses echolocation to sense movement on the surface
0:13:43 > 0:13:45of the river.
0:13:48 > 0:13:51Then it's time to go fishing.
0:13:54 > 0:13:59It's after a high-protein catch using minimal energy.
0:14:14 > 0:14:17Now, echolocation is all very well...
0:14:19 > 0:14:23..but in a constant arms race between predator and prey...
0:14:25 > 0:14:28..it's important for bats to stay one step ahead.
0:14:30 > 0:14:34The tympanate moth has developed a remarkable response to
0:14:34 > 0:14:38echolocation - a rudimentary ear.
0:14:40 > 0:14:44If it senses an incoming sonic pulse,
0:14:44 > 0:14:47it takes immediate evasive action.
0:14:54 > 0:14:57But it may well have met its match.
0:15:02 > 0:15:04This is the long-eared bat.
0:15:11 > 0:15:17It still uses echolocation, but when it gets close to its prey,
0:15:17 > 0:15:19it enters stealth mode.
0:15:21 > 0:15:28It switches off its targeting mechanism and instead relies
0:15:28 > 0:15:31on a far more conventional sense.
0:15:38 > 0:15:42It's able to hear even the slightest movements
0:15:42 > 0:15:44thanks to its enormous ears.
0:15:49 > 0:15:52It's now a game of patience.
0:15:52 > 0:15:57All the moth has to do is stay perfectly still.
0:15:58 > 0:16:00One tiny move...
0:16:03 > 0:16:05..and it's all over.
0:16:20 > 0:16:24In New Zealand, these short-tailed bats can fly and echolocate
0:16:24 > 0:16:26just like other species.
0:16:31 > 0:16:35But here, the most energy-rich prey isn't in the air.
0:16:37 > 0:16:39It's actually on the forest floor.
0:16:43 > 0:16:45So that's where they hunt.
0:16:49 > 0:16:51Mirroring the behaviour of the shrew-like animals
0:16:51 > 0:16:53they evolved from.
0:17:04 > 0:17:08They're hunting large insects called wetas,
0:17:08 > 0:17:10using a combination of echolocation
0:17:10 > 0:17:13and a highly developed sense of smell.
0:17:21 > 0:17:23Their bodies have adapted, too.
0:17:27 > 0:17:32They fold their wings away into special sheaths on their backs,
0:17:32 > 0:17:35allowing them to walk on their elbows.
0:17:41 > 0:17:45They also have particularly strong hind limbs
0:17:45 > 0:17:49and a robust pelvis, just like their ground-living ancestors.
0:17:58 > 0:18:03These bats have effectively turned the clock back 60 million years
0:18:03 > 0:18:06in order to maximise the potential of their environment.
0:18:14 > 0:18:18But there is one species that needs to find a much bigger victim
0:18:18 > 0:18:20in order to survive.
0:18:24 > 0:18:29Vampire bats are the only mammals to feed entirely on blood.
0:18:32 > 0:18:37And it couldn't be achieved without some astonishing senses.
0:19:12 > 0:19:15These bats only eat at night,
0:19:15 > 0:19:18approaching their quarry
0:19:18 > 0:19:22as quietly as possibly by crawling on the ground.
0:19:24 > 0:19:29When they're close, their super-senses kick in.
0:19:36 > 0:19:40Tiny heat receptors in their nose leaf can detect the most
0:19:40 > 0:19:45blood-rich veins on an animal, from up to 20 centimetres away.
0:19:48 > 0:19:52These highly specialised nerve cells are similar to the
0:19:52 > 0:19:56pain-detecting cells found in the human tongue that warn us
0:19:56 > 0:19:58when something's too hot.
0:20:07 > 0:20:12Vampire bats may feed on a pig for up to 30 minutes
0:20:12 > 0:20:16and they can consume 25ml of blood.
0:20:24 > 0:20:26A highly effective anti-coagulant in
0:20:26 > 0:20:30their saliva ensures that the blood keeps flowing.
0:20:32 > 0:20:34There's only one problem.
0:20:34 > 0:20:37When they've had their fill...
0:20:37 > 0:20:40they weigh too much to fly.
0:20:43 > 0:20:46But they've got ultra-efficient kidneys,
0:20:46 > 0:20:49which, within a few minutes can process the blood,
0:20:49 > 0:20:54so they can immediately urinate and rid themselves of the excess plasma.
0:20:56 > 0:21:00Their load lightened, they can soon fly away.
0:21:05 > 0:21:10Bats' sophisticated senses help them replenish their energy.
0:21:15 > 0:21:18But then they have to find the fastest way home,
0:21:18 > 0:21:21otherwise they're simply going to burn up all of that
0:21:21 > 0:21:23energy they've just acquired.
0:21:25 > 0:21:30And how bats find their way back to their roost, night after night,
0:21:30 > 0:21:32has always been a mystery.
0:21:38 > 0:21:44But now scientists think they might have located the answer.
0:21:48 > 0:21:52A new study has found that, in order to do this,
0:21:52 > 0:21:56bats are able to utilise a completely different sense.
0:22:02 > 0:22:06They've discovered tiny iron oxide particles
0:22:06 > 0:22:08inside some bats' brains.
0:22:14 > 0:22:19These may give them an internal compass...
0:22:24 > 0:22:28..which may help them find the most direct route back to their roosts.
0:22:37 > 0:22:42Using magnetoreception in this way puts bats into a select
0:22:42 > 0:22:47group of animals that are capable of using the Earth's natural magnetism
0:22:47 > 0:22:49to navigate the planet.
0:22:53 > 0:22:59So this could help them efficiently find their way back to their roost
0:22:59 > 0:23:01and it's here that they've come up
0:23:01 > 0:23:03with some neat tricks to conserve energy.
0:23:17 > 0:23:19Most bats rest during the day...
0:23:22 > 0:23:26..and sometimes in the most surprising places.
0:23:31 > 0:23:35These Mexican free-tailed bats live under the
0:23:35 > 0:23:38Congress Avenue Bridge in Austin, Texas.
0:23:50 > 0:23:55Tent-making bats in Honduras seek sanctuary
0:23:55 > 0:23:57by building a home under leaves.
0:24:00 > 0:24:03Once they find a suitable leaf, they chew through
0:24:03 > 0:24:07the midrib before folding it in half to create a tent-shaped shelter.
0:24:09 > 0:24:14Perfect protection from sun, wind and rain.
0:24:19 > 0:24:24In Borneo, caves provide a sanctuary where bats can roost,
0:24:24 > 0:24:28safe from predators, as they rest after a night's flying.
0:24:35 > 0:24:38Here, up to three million wrinkle-lipped bats might
0:24:38 > 0:24:40live in a single colony.
0:24:43 > 0:24:45The problem is,
0:24:45 > 0:24:48it's cold and trying to keep warm uses up
0:24:48 > 0:24:51valuable energy.
0:24:53 > 0:24:57To combat this, the bats cluster tightly together,
0:24:57 > 0:24:59sharing their body heat.
0:25:00 > 0:25:04It's so effective that their huddles can actually raise
0:25:04 > 0:25:07the ambient temperature of the cave
0:25:07 > 0:25:09by up to ten degrees centigrade.
0:25:14 > 0:25:18But huddling isn't enough for the bats living in Northern Canada,
0:25:18 > 0:25:22where the temperature can drop to 20 degrees below zero.
0:25:29 > 0:25:33Here, bats have to rely on their specialised physiology
0:25:33 > 0:25:35to pull them through.
0:25:41 > 0:25:45These brown bats have been here throughout the freezing winter.
0:25:47 > 0:25:49As the thermal imaging camera shows,
0:25:49 > 0:25:52their bodies are the same temperature as their
0:25:52 > 0:25:57surroundings despite being warm-blooded animals.
0:25:59 > 0:26:01This is because the bats
0:26:01 > 0:26:04have shut down their bodies to preserve energy.
0:26:05 > 0:26:09They switch off the blood supply to their limbs
0:26:09 > 0:26:14and slow their heart rate to just ten beats a minute.
0:26:16 > 0:26:18And in this deactivated state,
0:26:18 > 0:26:24they can survive on a single breath every 90 minutes.
0:26:26 > 0:26:30They've been known to stay in a state of torpor, like this,
0:26:30 > 0:26:32for up to 140 days.
0:26:36 > 0:26:41And when it's time to wake up, they begin a well-rehearsed ritual.
0:26:44 > 0:26:50They raise their heart rate and then use a special patch of fat
0:26:50 > 0:26:54above their shoulders to warm their blood, pumping it around their body.
0:26:57 > 0:27:01So after just ten minutes, they are fully active again.
0:27:05 > 0:27:07Even in the summer months,
0:27:07 > 0:27:12they can conserve energy by entering what's known as daily torpor.
0:27:14 > 0:27:20A crucial adaptation to survive when times are tough.
0:27:31 > 0:27:34A unique combination of remarkable anatomy...
0:27:39 > 0:27:41..amazing physiology...
0:27:46 > 0:27:49..and surprising senses...
0:27:53 > 0:27:56..has enabled bats to thrive wherever they live.
0:28:04 > 0:28:07There are 1,240 species worldwide.
0:28:11 > 0:28:14They are so successful, they represent
0:28:14 > 0:28:17more than 20% of all the mammal species
0:28:17 > 0:28:19we currently have on Earth.
0:28:25 > 0:28:28And that's the wonder of bats!