Animals Through the Night: Sleepover at the Zoo

0:00:02 > 0:00:04We're about to embark on an ambitious project

0:00:04 > 0:00:06to explore the fascinating world of animal sleep.

0:00:06 > 0:00:08We do know a lot about the animal kingdom,

0:00:08 > 0:00:12the evolution of species, their ecology and physiology,

0:00:12 > 0:00:15but there are still a few gaps in our knowledge

0:00:15 > 0:00:19and one of the greatest mysteries has been the nature and function

0:00:19 > 0:00:23of sleep, something that science is only just beginning to understand.

0:00:24 > 0:00:27'Tonight we'll be attempting something

0:00:27 > 0:00:29'that's never been done before.

0:00:29 > 0:00:32'Bristol Zoo will play host to a unique research project.

0:00:32 > 0:00:36'For the first time we'll compare and contrast

0:00:36 > 0:00:41'different animal sleep patterns across the course of a single night.

0:00:41 > 0:00:44'To build up this unprecedented snapshot,

0:00:44 > 0:00:46'we've rigged 20 of the enclosures

0:00:46 > 0:00:48'with night-vision cameras and sensors,

0:00:48 > 0:00:52'and we'll be monitoring just what the animals get up to

0:00:52 > 0:00:53'after dark.'

0:00:53 > 0:00:56Look at them. Look at them playing together!

0:00:56 > 0:00:58'And we won't just be at the zoo,

0:00:58 > 0:01:02'we'll be taking an in-depth look at animal sleep research

0:01:02 > 0:01:04'around the world.'

0:01:04 > 0:01:06It's, I think, been one of the great success stories

0:01:06 > 0:01:08of neuroscience over the past 15, 20 years.

0:01:08 > 0:01:11'We'll be looking at dolphins.

0:01:11 > 0:01:14'These marine mammals spend their entire lives in the water,

0:01:14 > 0:01:16'but they must come to the surface to breathe.

0:01:16 > 0:01:19'So, how can they get a good night's sleep?

0:01:19 > 0:01:22'Can a sleeping meerkat's brain distinguish between different noises

0:01:22 > 0:01:27'at night, and tell it when to wake up in the face of a threat?'

0:01:27 > 0:01:32A meerkat left the nest box at our level 4 meerkat alarm call.

0:01:34 > 0:01:37'And this cat is asleep, but what is it doing?

0:01:38 > 0:01:43'Is this evidence that animals can dream?

0:01:43 > 0:01:45'We'll see how throughout evolution

0:01:45 > 0:01:49'the process of sleep has not only been conserved

0:01:49 > 0:01:51'but perfected and advanced.

0:01:53 > 0:01:56'And we'll explore how the study of animals

0:01:56 > 0:01:59'can begin to unlock the secrets of human sleep.'

0:02:01 > 0:02:04I'm fascinated by the underlying mechanisms

0:02:04 > 0:02:06that determine how animals sleep,

0:02:06 > 0:02:09and I'll be finding out why the latest research

0:02:09 > 0:02:13is forcing us to rethink the role of sleep throughout the animal kingdom.

0:02:21 > 0:02:26Animal sleep is more varied than we could possibly have imagined,

0:02:26 > 0:02:28and Bristol Zoo,

0:02:28 > 0:02:31with more than 400 species in 12 acres,

0:02:31 > 0:02:34gives us the perfect opportunity to see for the first time

0:02:34 > 0:02:36how the animals behave during the night.

0:02:38 > 0:02:41Around 600,000 people visit the zoo each year,

0:02:41 > 0:02:45but every night the lights go off, the visitors leave

0:02:45 > 0:02:47and the animals are left alone.

0:02:49 > 0:02:51Our cameras are already in place,

0:02:51 > 0:02:56but connecting them to our HQ needs more than 6km of cable,

0:02:56 > 0:03:00and we can't finish rigging until all the guests have gone.

0:03:05 > 0:03:08OK, it's 5pm, the last of the visitors are leaving,

0:03:08 > 0:03:10the zookeepers will be heading home very shortly

0:03:10 > 0:03:13and of course normally nobody gets to stay here overnight -

0:03:13 > 0:03:15until tonight, that is -

0:03:15 > 0:03:19and by morning we should have a good picture of how the whole zoo sleeps.

0:03:19 > 0:03:21Right, that's the last of them gone.

0:03:21 > 0:03:23Team, that's the zoo closed.

0:03:23 > 0:03:25RADIO: 'OK, thanks, Liz.'

0:03:28 > 0:03:30'The cameras are starting to come online,

0:03:30 > 0:03:33'and we're getting our first glimpse of the animals.

0:03:34 > 0:03:37'Animal activity patterns are divided into four

0:03:37 > 0:03:39'basic categories -

0:03:39 > 0:03:41'diurnal, nocturnal,

0:03:41 > 0:03:43'crepuscular and cathemeral -

0:03:43 > 0:03:47'and there are animals in all of these categories at the zoo.

0:03:47 > 0:03:49'Humans are diurnal animals -

0:03:49 > 0:03:52'we're active during the day and we sleep at night.

0:03:52 > 0:03:56'The gorillas, flamingos and seals should follow this pattern.

0:03:57 > 0:03:59'A nocturnal animal is the opposite,

0:03:59 > 0:04:02'active at night and asleep during the day.

0:04:02 > 0:04:05'So the red pandas, sloths and crocodiles

0:04:05 > 0:04:07'should be awake all night.

0:04:09 > 0:04:12'Crepuscular animals are mainly active at dawn and dusk,

0:04:12 > 0:04:15'using the most temperate part of the day to feed.

0:04:16 > 0:04:20'Watch out for the tapirs, capybaras and fruit bats

0:04:20 > 0:04:22'following this pattern tonight.

0:04:24 > 0:04:26'And finally cathemeral animals -

0:04:26 > 0:04:30'only the lions fit into this category at the zoo.

0:04:30 > 0:04:33'These animals can be active at any time of the day or night.

0:04:35 > 0:04:39'But these four categories only dictate the timing of sleep -

0:04:39 > 0:04:44'we're watching for a huge variety of other behaviours as well.

0:04:44 > 0:04:48'The cameras feed into the theatre at the centre of the zoo.

0:04:48 > 0:04:51'This is our HQ for the night.'

0:04:51 > 0:04:54I've just grabbed John Partridge, Senior Curator here at the zoo,

0:04:54 > 0:04:56for a quick chat by the lion enclosure.

0:04:56 > 0:04:58John, what do you make of all of this tonight?

0:04:58 > 0:04:59- This is all very exciting.- Is it?

0:04:59 > 0:05:02We're really looking forward to seeing what's going to be found,

0:05:02 > 0:05:04really, with our animals.

0:05:04 > 0:05:06We leave them quite a lot to their own devices at night,

0:05:06 > 0:05:08let them get on with what they want to do.

0:05:08 > 0:05:09The lions behind us, particularly,

0:05:09 > 0:05:11we know will be active during the night,

0:05:11 > 0:05:14- but we don't know exactly what they get up to.- So you don't mind us

0:05:14 > 0:05:17laying all these cables down and invading the space back there?

0:05:17 > 0:05:19Not at all. Let's see what happens,

0:05:19 > 0:05:22- I'm sure there'll be a lot of interesting things.- Good stuff.

0:05:22 > 0:05:24Well, come in and have a look at the monitors with us later on.

0:05:24 > 0:05:27- I'd love to do that, thank you. - Excellent. Thanks, John.

0:05:28 > 0:05:32What sleep IS seems such an obvious question.

0:05:32 > 0:05:35But it's much more complex than we think.

0:05:35 > 0:05:39Across the animal kingdom, sleep is as varied as life itself.

0:05:42 > 0:05:45From the amount of sleep animals get -

0:05:45 > 0:05:47giraffes sleep as little as four hours a day,

0:05:47 > 0:05:51and little brown bats sleep for nearly 20 hours -

0:05:51 > 0:05:53to sleep behaviours.

0:05:53 > 0:05:57Different animals choose different places to sleep.

0:05:57 > 0:05:59They adopt different body positions.

0:05:59 > 0:06:01Like the leaf-tailed gecko, for example,

0:06:01 > 0:06:05which always sleeps vertically, using tree bark as camouflage.

0:06:05 > 0:06:08Some have adaptations so unusual

0:06:08 > 0:06:11that scientists are still not sure what they're for.

0:06:11 > 0:06:14Parrot fish sleep in a cocoon made from mucus

0:06:14 > 0:06:16secreted from their mouths.

0:06:16 > 0:06:19This could be to protect themselves from parasites

0:06:19 > 0:06:22or to prevent their scent drifting, attracting predators.

0:06:22 > 0:06:25Other animals have sleep rituals.

0:06:25 > 0:06:30They circle, yawn, stretch or make a nest like this chimpanzee.

0:06:31 > 0:06:34Sleeping in groups is common across the animal kingdom.

0:06:34 > 0:06:36There's safety in numbers.

0:06:36 > 0:06:40Often, big groups will have sentry animals on alert for predators.

0:06:40 > 0:06:44And other animals remain vigilant during sleep.

0:06:44 > 0:06:46This kangaroo rat wakes quickly

0:06:46 > 0:06:48to the sound of a snake moving above.

0:06:51 > 0:06:56No-one has ever watched a zoo in this detail at night.

0:06:56 > 0:06:58As the animals fall asleep,

0:06:58 > 0:07:01we'll be looking out for never-before-seen behaviours

0:07:01 > 0:07:04that darkness usually conceals.

0:07:08 > 0:07:11Now, this is our control room,

0:07:11 > 0:07:15with video feeds from each of the enclosures that we're monitoring,

0:07:15 > 0:07:19and we've also got infrared motion sensors trained on our animals.

0:07:19 > 0:07:21This is the motion sensor panel -

0:07:21 > 0:07:23green means the animals are still moving,

0:07:23 > 0:07:26red means the animals haven't moved for 30 seconds or so,

0:07:26 > 0:07:28so it's likely they're asleep.

0:07:28 > 0:07:30But our experiment actually started a month ago

0:07:30 > 0:07:33when we started rigging the zoo with our cameras.

0:07:35 > 0:07:38Observing animal sleep is no easy task.

0:07:40 > 0:07:43The risk is that sleep research itself may disturb the animal,

0:07:43 > 0:07:46stopping it from sleeping.

0:07:46 > 0:07:48So it was essential we gave our subjects the time

0:07:48 > 0:07:51to become accustomed to the intrusion.

0:07:53 > 0:07:55And not all of them did.

0:07:55 > 0:07:59We rigged the pygmy hippo enclosure with four infrared cameras.

0:07:59 > 0:08:02Sirana, the young female, took one look at the cameras,

0:08:02 > 0:08:06hid in the water and refused to come out for two days,

0:08:06 > 0:08:09even after we removed the equipment.

0:08:10 > 0:08:14Which is why the hippos won't be part of our study tonight.

0:08:15 > 0:08:17Many of the other zoo residents

0:08:17 > 0:08:20seemed relatively unfazed by the process

0:08:20 > 0:08:22and after some initial curiosity,

0:08:22 > 0:08:26they've accepted our cameras and should sleep normally tonight.

0:08:28 > 0:08:31And then there was Jock, the male silverback gorilla.

0:08:31 > 0:08:34He recognizes cameras, and they upset him.

0:08:36 > 0:08:40So we'll be using camouflaged cameras already installed by the zoo

0:08:40 > 0:08:42in the newly-built gorilla house.

0:08:46 > 0:08:48Now, what happened there with Jock our gorilla

0:08:48 > 0:08:51is just one example of how difficult it can be

0:08:51 > 0:08:53to carry out animal sleep research.

0:08:53 > 0:08:54Just by studying sleep

0:08:54 > 0:08:57we can often interfere with the animals' natural behaviour.

0:08:57 > 0:09:01Helping us to collate and analyse our data this evening

0:09:01 > 0:09:03is one of the world's leading experts on animal sleep,

0:09:03 > 0:09:05Dr Bryson Voirin.

0:09:05 > 0:09:06Bryson, we've been trying very hard

0:09:06 > 0:09:08to habituate our animals to the cameras,

0:09:08 > 0:09:11give them time to get back into their natural behaviours,

0:09:11 > 0:09:14but one of the questions that kind of has to be raised

0:09:14 > 0:09:17is how valid will this data be? Because the animals are captive.

0:09:17 > 0:09:20Well, clearly there's going to be some major differences

0:09:20 > 0:09:21between a captive and a wild animal,

0:09:21 > 0:09:24but the data we have right now for most of these species

0:09:24 > 0:09:27is based on animals in a box or in a cage inside of a laboratory,

0:09:27 > 0:09:29so by setting it here in the zoo

0:09:29 > 0:09:31it's a much more naturalish environment

0:09:31 > 0:09:33than what's known right now.

0:09:36 > 0:09:37Bryson has been working with us

0:09:37 > 0:09:41to determine which animals to select for our observations tonight.

0:09:43 > 0:09:46He's been studying animal sleep for ten years,

0:09:46 > 0:09:48and he'll be able to interpret the data

0:09:48 > 0:09:50as our night at the zoo unfolds.

0:09:54 > 0:09:57Now, one of the methods used for studying sleep

0:09:57 > 0:09:59is direct behavioural observation.

0:09:59 > 0:10:02We've got two researchers here on our monitors

0:10:02 > 0:10:05who will be collecting all the data from our motion sensors,

0:10:05 > 0:10:06and by the end of the night,

0:10:06 > 0:10:08hopefully we'll be able to see

0:10:08 > 0:10:10what patterns of sleep are emerging.

0:10:12 > 0:10:13Our researchers

0:10:13 > 0:10:16are examining a range of behaviours.

0:10:16 > 0:10:19How active the animals are, how often they move,

0:10:19 > 0:10:21if their eyes are open,

0:10:21 > 0:10:23if their breathing has slowed,

0:10:23 > 0:10:27and, if they're sleeping, how deeply and for how long.

0:10:29 > 0:10:32By morning, we'll have seen what all the animals got up to

0:10:32 > 0:10:36during the night, and we'll be able to compare the data between species.

0:10:39 > 0:10:42Now, Bryson, how useful is observational research

0:10:42 > 0:10:43in sleep analysis?

0:10:43 > 0:10:46Well, you know, historically speaking a lot of the sleep research

0:10:46 > 0:10:49has been actually focused on behaviour observations

0:10:49 > 0:10:51so here we're using cameras to record their every move,

0:10:51 > 0:10:54and that's a key way to actually see what an animal's getting up to

0:10:54 > 0:10:56and to ascertain what the behaviour of sleep is.

0:10:56 > 0:10:59And there are so many things we need to learn about sleep.

0:10:59 > 0:11:00It's not just about quantity, right?

0:11:00 > 0:11:02There's a lot of other factors involved

0:11:02 > 0:11:04that, you know, we may gain insight to here.

0:11:04 > 0:11:07Absolutely. It's not just the amount that they're sleeping,

0:11:07 > 0:11:08it's also the sleep-related behaviours.

0:11:08 > 0:11:11Are they sleeping together, are they sleeping by themselves,

0:11:11 > 0:11:13are they sleeping in a particular way,

0:11:13 > 0:11:15are they doing strange behaviours that we wouldn't normally see?

0:11:15 > 0:11:17And so just by watching them

0:11:17 > 0:11:19sleeping here we can learn some very interesting things.

0:11:24 > 0:11:26OK, let's do our first monitor check of the evening.

0:11:26 > 0:11:28Could you bring up the gorillas for me?

0:11:31 > 0:11:32Lovely female, there, with her young.

0:11:32 > 0:11:35- They seem to be asleep, don't they? - Completely passed out.

0:11:38 > 0:11:42The gorillas are among the first of our animals to fall asleep

0:11:42 > 0:11:44and we can see the behavioural ritual Salome,

0:11:44 > 0:11:49the adult female gorilla, carries out each night before settling down.

0:11:51 > 0:11:54She leaves her platform with her baby on her back

0:11:54 > 0:11:57to gather fresh woodchip off the floor.

0:11:57 > 0:12:00She's very particular about what she chooses.

0:12:01 > 0:12:05She's using it to create a bed for her and her baby.

0:12:08 > 0:12:11Salome actively gathers bedding material

0:12:11 > 0:12:13and builds a new nest every night.

0:12:15 > 0:12:17This behaviour is common in great apes -

0:12:17 > 0:12:20chimpanzees and orang-utans also do this.

0:12:22 > 0:12:24It's a sleep ritual considered by scientists

0:12:24 > 0:12:27to be an example of tool use.

0:12:27 > 0:12:28Not only that,

0:12:28 > 0:12:33but it's a process that's taught by a mother to her young.

0:12:37 > 0:12:39By improving their quality of sleep,

0:12:39 > 0:12:41it's believed that the higher primates

0:12:41 > 0:12:45are able to enhance their waking survival skills.

0:12:45 > 0:12:47With a little encouragement from Salome,

0:12:47 > 0:12:51it takes mother and baby just half an hour to settle down to sleep.

0:12:54 > 0:12:56Now it's time for a little tour of our zoo,

0:12:56 > 0:12:59introduce you to some of the animals that we're monitoring -

0:12:59 > 0:13:01first up, the Asiatic lions. See you in a bit.

0:13:05 > 0:13:07There is definitely something a bit weird

0:13:07 > 0:13:10about walking through a deserted zoo at night.

0:13:10 > 0:13:14Most primates, including humans, are monophasic,

0:13:14 > 0:13:18which means they get all their sleep in one go.

0:13:18 > 0:13:20All other animals are polyphasic,

0:13:20 > 0:13:23they sleep in a number of short phases.

0:13:23 > 0:13:27So the gorillas should now sleep through the night.

0:13:29 > 0:13:32For the rest of the animals, this is the beginning of a cycle

0:13:32 > 0:13:36which will see them sleeping and waking several times.

0:13:36 > 0:13:39So we anticipate plenty of activity at the zoo tonight.

0:13:42 > 0:13:45I'm here with Lynsey, assistant curator of mammals

0:13:45 > 0:13:49and her two favourite animals in the zoo, yeah?

0:13:49 > 0:13:52The two beautiful lions that we just saw there.

0:13:52 > 0:13:53Tell me a little bit about them.

0:13:53 > 0:13:57These are two brothers, their names are Ketan and Kamran,

0:13:57 > 0:14:00they are just turned one year old.

0:14:00 > 0:14:04They are actually hand-reared, by me and a small team of keepers here.

0:14:04 > 0:14:07- That's no small feat. - It was certainly no small feat.

0:14:07 > 0:14:11They're very small to start with, quite a lot of intensive work.

0:14:11 > 0:14:14OK. How much do you know of what they do at night here?

0:14:14 > 0:14:16Very little, really.

0:14:16 > 0:14:18We come in - obviously we know what goes on in the day very well -

0:14:18 > 0:14:20we get clues when we come in in the morning

0:14:20 > 0:14:23as to where they've been and where they've possibly slept.

0:14:23 > 0:14:25You see the beds that they've made their own.

0:14:25 > 0:14:28But where they've spent all night, or whether it's part of the night

0:14:28 > 0:14:31- we actually have no idea, so I'm fascinated to see the results.- Good.

0:14:31 > 0:14:33Well, come and have a look at our monitors later on

0:14:33 > 0:14:35- and we'll see how they're getting on.- Absolutely.

0:14:35 > 0:14:37Thank you so much for introducing me to them,

0:14:37 > 0:14:39- they're beautiful.- No problem.

0:14:42 > 0:14:44We know that the lions are cathemeral,

0:14:44 > 0:14:47so they probably won't sleep through the night.

0:14:48 > 0:14:51But what we don't know is how often they'll wake

0:14:51 > 0:14:53and what they'll get up to when they do.

0:14:57 > 0:15:02OK, so on the right up here we should have some tapirs.

0:15:02 > 0:15:04Now, they're herbivores

0:15:04 > 0:15:08and they tend to be sleeping and active in cycles

0:15:08 > 0:15:11all through the day and night so we might get a bit of action from them.

0:15:11 > 0:15:14Ooh, I can hear something in the water. Turn the light on them.

0:15:14 > 0:15:16Oh, look at that!

0:15:16 > 0:15:17Hello.

0:15:17 > 0:15:19So these guys, all through the night,

0:15:19 > 0:15:22will go through phases of sleep and then they'll wake up,

0:15:22 > 0:15:26and in the wild it's just to allow them to feed as much as possible

0:15:26 > 0:15:29all through the day and night because they're herbivores

0:15:29 > 0:15:31and they need to get a lot of food into them

0:15:31 > 0:15:33to get the energy they need.

0:15:34 > 0:15:36Now, we don't want to disturb them too much,

0:15:36 > 0:15:38and of course we are still using a white light right now

0:15:38 > 0:15:40because it hasn't been dark for long,

0:15:40 > 0:15:42but later on we might have a little sneak around

0:15:42 > 0:15:44and we'll use infrared lights

0:15:44 > 0:15:47to really make sure we don't disturb any of the animals

0:15:47 > 0:15:49once they've really settled in for the night.

0:15:49 > 0:15:51But it is a bit of a treat to see them.

0:15:51 > 0:15:52HIGH-PITCHED CALL

0:15:52 > 0:15:54And they're vocalising as well.

0:15:55 > 0:15:57Very interesting looking animals.

0:15:57 > 0:15:59OK, let's leave them in peace.

0:16:05 > 0:16:09The crepuscular tapirs will be most active at dusk and dawn,

0:16:09 > 0:16:13but they can still wake in the middle of the night to feed.

0:16:13 > 0:16:16How often will they wake and how active will they be?

0:16:20 > 0:16:22Across the zoo are the flamingos.

0:16:22 > 0:16:25They're diurnal, so they should sleep at night,

0:16:25 > 0:16:29but right now they're still active and communicating with each other.

0:16:29 > 0:16:33We want to monitor their behaviour as a group through the night.

0:16:35 > 0:16:37And then there are those animals

0:16:37 > 0:16:41that have turned the daily cycle of activity and rest on its head.

0:16:43 > 0:16:45All right, so in this enclosure

0:16:45 > 0:16:49we have got two red pandas -

0:16:49 > 0:16:52there's one - a male and a female.

0:16:52 > 0:16:57And they are nocturnal animals, so this is why they're out and about.

0:16:57 > 0:16:59They're actually more closely related to the raccoon

0:16:59 > 0:17:01than they are to the giant panda.

0:17:02 > 0:17:05And hopefully we'll get to see some more of their activity

0:17:05 > 0:17:08with our monitors later on.

0:17:16 > 0:17:19The red pandas should be up and about tonight.

0:17:20 > 0:17:23But with temperatures at the zoo already plummeting,

0:17:23 > 0:17:26will they be able to resist the warmth of their nest box?

0:17:35 > 0:17:38That sleep is so varied should perhaps not come as a surprise

0:17:38 > 0:17:40when you consider its origins.

0:17:42 > 0:17:47All life on earth evolved under the day-night cycle of the sun.

0:17:47 > 0:17:51So early life had one phase of activity and one phase of inactivity

0:17:51 > 0:17:53in line with light and dark.

0:17:57 > 0:18:00As animals evolved central nervous systems,

0:18:00 > 0:18:04so inactivity became what we would recognize as sleep,

0:18:04 > 0:18:09an opportunity for the brain and body to perform specific functions

0:18:09 > 0:18:11not carried out when the animal is active.

0:18:13 > 0:18:16Over hundreds of millions of years

0:18:16 > 0:18:21the functions performed during sleep became more and more complex.

0:18:25 > 0:18:28As life spread into every habitat on earth,

0:18:28 > 0:18:31so animals were forced to adapt the way they slept

0:18:31 > 0:18:33in order to survive and thrive.

0:18:39 > 0:18:42But light and dark are still some of the key triggers

0:18:42 > 0:18:44for the chemical processes in the brain

0:18:44 > 0:18:46that tell us when we should fall asleep.

0:18:53 > 0:18:56At Oxford University, some of the world's leading experts

0:18:56 > 0:18:59in the sleep-wake cycles of all life on earth

0:18:59 > 0:19:02are breaking new ground with their research

0:19:02 > 0:19:04by studying the neurochemistry at work.

0:19:08 > 0:19:12Russell Foster is professor of circadian neuroscience

0:19:12 > 0:19:13at the university.

0:19:18 > 0:19:21Russell, clearly sleep is hugely important in all animals,

0:19:21 > 0:19:23otherwise they wouldn't have retained it -

0:19:23 > 0:19:27but how much do we know is going on at a physiological level,

0:19:27 > 0:19:28inside the brain?

0:19:28 > 0:19:31It's been incredible progress over the past 10, 15 years,

0:19:31 > 0:19:32and I think the first point to make

0:19:32 > 0:19:35is that sleep doesn't arise from a single structure within the brain -

0:19:35 > 0:19:37in fact, what's turned out to be remarkable

0:19:37 > 0:19:40is that there are multiple brain structures

0:19:40 > 0:19:43and multiple brain chemicals, neurotransmitters, involved in sleep.

0:19:43 > 0:19:46But I think we can think of three essential elements

0:19:46 > 0:19:47as regulating sleep.

0:19:47 > 0:19:50First is the light-dark cycle, the detection of light.

0:19:50 > 0:19:52Then there's the master body clock,

0:19:52 > 0:19:54telling the brain when it's an appropriate time to be awake

0:19:54 > 0:19:57and when it's an appropriate time to be asleep.

0:19:57 > 0:19:59And then, finally, there's the intuitive part about sleep,

0:19:59 > 0:20:02which is the longer you've been awake the greater the sleep pressure,

0:20:02 > 0:20:04the greater the need for sleep.

0:20:04 > 0:20:07- So, there's three essential elements. - OK, so let's break them down -

0:20:07 > 0:20:10the first one, if it's about reacting to environmental cues,

0:20:10 > 0:20:13to light and dark, how does that work?

0:20:13 > 0:20:16So for us, if you increase the amount of light,

0:20:16 > 0:20:19then we feel more alert - decrease the amount of light,

0:20:19 > 0:20:21we're more likely to drop to sleep.

0:20:21 > 0:20:23Of course, if it's a nocturnal animal it's the reverse.

0:20:23 > 0:20:26Now, the assumption has been for years, 150 years,

0:20:26 > 0:20:30that all light detection is by the classical visual system,

0:20:30 > 0:20:31the rods and the cones.

0:20:31 > 0:20:34The rods providing us with our sense of dim light vision

0:20:34 > 0:20:37and the cones our sense of colour and of contrast.

0:20:37 > 0:20:40- All channelling to the optic nerve. - All channelling to the optic nerve.

0:20:40 > 0:20:43But what we discovered is that there's a third class of light sensor

0:20:43 > 0:20:46within the eye, and it's based upon the ganglion cells.

0:20:46 > 0:20:49Now, the ganglion cells are actually those cells in the eye

0:20:49 > 0:20:51that form the optic nerve,

0:20:51 > 0:20:55and about one or two out of every hundred of those ganglion cells

0:20:55 > 0:20:57are directly light-sensitive,

0:20:57 > 0:20:59and are not projecting to the visual structures in the brain,

0:20:59 > 0:21:03but going to the structures in the brain that are regulating sleep.

0:21:03 > 0:21:06So it's nothing to do with actually being able to see or not see,

0:21:06 > 0:21:08it's just about the brain registering

0:21:08 > 0:21:10- there's light or there's no light. - That's right.

0:21:10 > 0:21:12In fact, that's this new understanding of the eye.

0:21:12 > 0:21:15In a sense we've known forever that it's given us our sense of space,

0:21:15 > 0:21:17but we've never really fully appreciated

0:21:17 > 0:21:20that it also helps us give our sense of time

0:21:20 > 0:21:23and has a profound influence upon our sleep and wake systems.

0:21:23 > 0:21:25If we look at this model of the brain here,

0:21:25 > 0:21:29we see that the optic nerves here and the eyes will be sort of here...

0:21:29 > 0:21:31They're coming through this way...

0:21:31 > 0:21:33They form a little bridge called the optic chiasm,

0:21:33 > 0:21:36but also fairly close to it is the VLPO,

0:21:36 > 0:21:38or the ventrolateral preoptic nuclei.

0:21:38 > 0:21:40- We'll call it the VLPO. - We'll call it the VLPO.

0:21:40 > 0:21:42It's also known as the sleep switch,

0:21:42 > 0:21:45and it's called the sleep switch because it sends projections

0:21:45 > 0:21:47all the way down to the hindbrain, here,

0:21:47 > 0:21:51and the hindbrain contains the structures which then feed forward

0:21:51 > 0:21:53and bathe our cortex,

0:21:53 > 0:21:56this, in neurotransmitters that keep us awake.

0:21:58 > 0:22:01So the light-dark message goes straight to the sleep switch

0:22:01 > 0:22:05or VLPO, and in diurnal animals tells the brain to sleep

0:22:05 > 0:22:06when it's dark.

0:22:10 > 0:22:12But if this were the only system at play,

0:22:12 > 0:22:15we would all fall asleep as soon the sun sets.

0:22:16 > 0:22:18Another system regulates this.

0:22:18 > 0:22:20Russell has carried out an experiment

0:22:20 > 0:22:22to show how it works in a mouse.

0:22:24 > 0:22:27What we see here, first of all, is a mouse in the dark.

0:22:27 > 0:22:31It's a nocturnal animal, and so it's wandering around.

0:22:31 > 0:22:33What I'm going to do in a moment is turn the lights on,

0:22:33 > 0:22:35and you'll see that within a short

0:22:35 > 0:22:38time it'll actually induce sleep. The mouse will go to sleep.

0:22:38 > 0:22:43So if we advance the footage, we see the lights have gone on...

0:22:43 > 0:22:46- And the mouse is asleep. - And the mouse is asleep.

0:22:46 > 0:22:50As you'd expect from this light regulation system.

0:22:50 > 0:22:52- This acute effect of light on sleep. - OK.

0:22:52 > 0:22:54But of course we've also got the body clock.

0:22:54 > 0:22:57What we're going to do next is just keep the lights on

0:22:57 > 0:22:58and just see what happens.

0:22:58 > 0:23:00For how long do you keep the lights on?

0:23:00 > 0:23:02Oh, we could keep the lights on for days,

0:23:02 > 0:23:04- so it'll be constant light.- OK.

0:23:06 > 0:23:10So, now this mouse has been under constant light for several days.

0:23:10 > 0:23:13So normally, of course, light would acutely put the mouse to sleep -

0:23:13 > 0:23:15and do you see here?

0:23:15 > 0:23:18The body clock is triggering activity.

0:23:18 > 0:23:22So even though the lights remain on and it should go to sleep,

0:23:22 > 0:23:26it will actually have periods of activity and sleep,

0:23:26 > 0:23:29just as if it was under a light-dark cycle.

0:23:30 > 0:23:33'The internal body clock tells each animal

0:23:33 > 0:23:37'when it should be asleep, and when it should be waking up,

0:23:37 > 0:23:40'fine-tuning the acute response to light and dark.'

0:23:42 > 0:23:45Now, of course, because that isn't complex enough,

0:23:45 > 0:23:49there is another mechanism at play - homeostatic regulation.

0:23:49 > 0:23:50Talk me through that.

0:23:50 > 0:23:53Well, I suppose it's the intuitive part about sleep.

0:23:53 > 0:23:54The longer you've been awake,

0:23:54 > 0:23:57the greater the sleep pressure that builds up.

0:23:57 > 0:24:00And when you're asleep, the sleep pressure is reversed.

0:24:00 > 0:24:02So what are the drivers of this system?

0:24:02 > 0:24:05Well, until fairly recently, we had very little idea.

0:24:05 > 0:24:07But the build-up of adenosine in the brain

0:24:07 > 0:24:09seems to be part of that sleep pressure.

0:24:09 > 0:24:11Now, it's a really interesting substance,

0:24:11 > 0:24:14because adenosine is the breakdown product from ATP,

0:24:14 > 0:24:18and ATP is the energy currency of cells.

0:24:18 > 0:24:22- So it's a great marker of how long they've been active.- A-ha.

0:24:22 > 0:24:26So you're making energy, adenosine is a by-product, it builds up...

0:24:26 > 0:24:27and then what happens?

0:24:27 > 0:24:30Well, we know that there are adenosine receptors

0:24:30 > 0:24:34in the ventrolateral preoptic nuclei, the VLPO, the sleep switch!

0:24:34 > 0:24:37And so what's happening is that pressure is building

0:24:37 > 0:24:41stronger and stronger on the VLPO until it gets to a critical level.

0:24:41 > 0:24:44And then the VLPO is turned on and you go into sleep.

0:24:44 > 0:24:46It's just got this incredible elegance and beauty,

0:24:46 > 0:24:49because they're all complementing and interacting

0:24:49 > 0:24:51to generate what is, after all,

0:24:51 > 0:24:54the single most important behaviour we experience.

0:24:55 > 0:25:00Around the zoo these three systems are driving sleep.

0:25:01 > 0:25:06The gorillas went to sleep almost as soon as the sun set.

0:25:09 > 0:25:10Before it went dark,

0:25:10 > 0:25:13the seals all began positioning themselves on the rocks

0:25:13 > 0:25:15in readiness for sleep.

0:25:17 > 0:25:19And all of the animals around the zoo

0:25:19 > 0:25:22will experience the adenosine system at work.

0:25:22 > 0:25:26The longer they're awake, the greater the pressure to sleep.

0:25:28 > 0:25:32But animals have also evolved to ensure they get sleep

0:25:32 > 0:25:34when it's most suitable -

0:25:34 > 0:25:37when they don't need to feed, and when it's safe.

0:25:46 > 0:25:51OK, it's 10:45. Bryson, anything of interest to look at so far?

0:25:51 > 0:25:53So, right here the tapirs are having a snack.

0:25:53 > 0:25:55OK, that's quite typical of tapirs - they graze,

0:25:55 > 0:25:57they sleep on and off all day and night.

0:25:57 > 0:26:00They were super-active when we went out to see them as well, in fact.

0:26:00 > 0:26:02- What about the...? - There's the red panda, actually,

0:26:02 > 0:26:04- he just came back in his nest box. - Ahh! Excellent.

0:26:04 > 0:26:06- So, they are nocturnal animals... - Mm-hm.

0:26:06 > 0:26:09Let's go over here and have a look at these other monitors.

0:26:09 > 0:26:11Could you bring up the seals for us?

0:26:13 > 0:26:15See, they were quite active not so long ago,

0:26:15 > 0:26:17and now they do look like they've gone to sleep -

0:26:17 > 0:26:20- but it's a little bit too early to tell, isn't it?- Absolutely.

0:26:20 > 0:26:25The seals are diurnal so they should be sleeping,

0:26:25 > 0:26:26but they seem restless.

0:26:26 > 0:26:29On previous nights, our cameras have shown

0:26:29 > 0:26:31that they usually sleep by now.

0:26:32 > 0:26:35Could something be keeping them awake tonight?

0:26:37 > 0:26:40Since we saw them earlier, Kamran and Ketan the lion cubs

0:26:40 > 0:26:44have settled, huddled together for warmth.

0:26:44 > 0:26:47This is the first phase of sleep, but it won't be their last.

0:26:53 > 0:26:56Animals which sleep in groups behave very differently

0:26:56 > 0:26:57from solitary animals.

0:26:59 > 0:27:02Around the zoo there are several large animal groups.

0:27:08 > 0:27:11In the wild, flamingos are particularly vulnerable

0:27:11 > 0:27:14to predators, especially at night.

0:27:14 > 0:27:17We can see that our zoo flamingos spend most of their day

0:27:17 > 0:27:20on the banks of their lake, but as darkness falls

0:27:20 > 0:27:23they all begin to move into the relative safety of the water,

0:27:23 > 0:27:25in readiness for sleep.

0:27:28 > 0:27:30Now, there are many advantages to sleeping in a group

0:27:30 > 0:27:32and one particularly interesting adaption

0:27:32 > 0:27:36is that oftentimes you'll see individuals on the outside

0:27:36 > 0:27:39of a group exhibiting a lighter form of sleep

0:27:39 > 0:27:42so that the ones in the centre can get more rest.

0:27:42 > 0:27:45Now, this is true of flocks of flamingos, for example,

0:27:45 > 0:27:49but take a look at this - it also seems to happen with insects.

0:27:51 > 0:27:54Professor Nigel Franks has been studying ants

0:27:54 > 0:27:57for more than 30 years, and his discoveries

0:27:57 > 0:28:00have revolutionised our understanding of ant behaviour.

0:28:00 > 0:28:04His first challenge was to identify when an ant is sleeping.

0:28:06 > 0:28:09You see them being utterly stationary,

0:28:09 > 0:28:11to the naked eye they look as if they're dead.

0:28:11 > 0:28:13They're that stationary.

0:28:13 > 0:28:15But the other thing is they have a little bit of a sort of posture

0:28:15 > 0:28:17about this, they pull in their antennae

0:28:17 > 0:28:20and pull in their legs as if not to take up too much space,

0:28:20 > 0:28:22and they'll have this particular posture.

0:28:24 > 0:28:26But ants live in colonies,

0:28:26 > 0:28:29and Nigel is an expert in how they work together

0:28:29 > 0:28:31to optimise their inactive phases.

0:28:34 > 0:28:37Nigel has come to a pine forest in Somerset

0:28:37 > 0:28:39to collect ants for our study.

0:28:41 > 0:28:44But finding ants in a forest is like -

0:28:44 > 0:28:45well, finding ants in a forest.

0:28:48 > 0:28:50The first thing we want to do, really,

0:28:50 > 0:28:56is find some mature pine trees that are over a fairly open understorey,

0:28:56 > 0:28:59and the reason for that is you want the sunlight to get down

0:28:59 > 0:29:01to the forest floor.

0:29:01 > 0:29:04I mean, it's just a case of rooting around.

0:29:04 > 0:29:06Sometimes you find a nice dry patch.

0:29:13 > 0:29:15A nice slug, lovely woodlice.

0:29:17 > 0:29:19None of our friends, yet.

0:29:19 > 0:29:22Oof! Yep, too wet.

0:29:24 > 0:29:28Nigel is looking for a colony which, in its nest,

0:29:28 > 0:29:31will occupy a space barely bigger than a two pence piece.

0:29:34 > 0:29:35We'll try this one.

0:29:45 > 0:29:46Well, got them.

0:29:46 > 0:29:48Fantastic.

0:29:49 > 0:29:53Nigel now needs to collect the complete ant colony,

0:29:53 > 0:29:56wood and all, and transport it back to the lab.

0:30:00 > 0:30:02Ants are eusocial,

0:30:02 > 0:30:06the highest recognized level of animal sociability.

0:30:07 > 0:30:11The life of each individual is adapted for the good of the colony.

0:30:12 > 0:30:15Workers have no offspring of their own,

0:30:15 > 0:30:18their sole purpose is to tend to the offspring of the queen.

0:30:18 > 0:30:21And these strict social habits

0:30:21 > 0:30:23are also evident in their sleep behaviours.

0:30:29 > 0:30:33Once Nigel is back in the lab, he transfers the colony

0:30:33 > 0:30:36to a specially prepared nest substitute,

0:30:36 > 0:30:39where they can be easily observed.

0:30:39 > 0:30:41Nigel then sets up a camera

0:30:41 > 0:30:44for us to study the ants over the course of a day.

0:30:44 > 0:30:49It's hard to see the patterns at normal speed,

0:30:49 > 0:30:52but here's what we see when the footage is sped up.

0:30:53 > 0:30:58The short periods of activity begin with just a few ants

0:30:58 > 0:31:00and grow like a chain reaction.

0:31:07 > 0:31:09At certain moments

0:31:09 > 0:31:12almost every member of the colony is stationary,

0:31:12 > 0:31:15and at other moments they're very much more active.

0:31:15 > 0:31:19And we've found that there's a rhythm to it.

0:31:19 > 0:31:24They're rhythmically active together and rhythmically inactive together.

0:31:25 > 0:31:29But we don't just see synchronised rest phases,

0:31:29 > 0:31:32we can also see another behaviour which the ants have developed

0:31:32 > 0:31:34to improve the sleep of the colony.

0:31:36 > 0:31:39When the main section of the colony is inactive,

0:31:39 > 0:31:42there seems to be a group of ants on sentry duty

0:31:42 > 0:31:44at the mouth of the nest.

0:31:44 > 0:31:47Professor Franks thinks that these may be a special type of ant

0:31:47 > 0:31:51within the group, on duty protecting the resting colony.

0:31:52 > 0:31:55Well, you've got a reasonably distinct group of ants

0:31:55 > 0:31:58near the entrance, and one of the things you'll notice

0:31:58 > 0:32:00is that they're always looking outwards

0:32:00 > 0:32:03ready to intercept foragers coming home,

0:32:03 > 0:32:07so you've got this wonderful sort of reception committee in the doorway,

0:32:07 > 0:32:10and that can prevent the beautiful rhythms

0:32:10 > 0:32:15inside the deep heart of the colony being disrupted.

0:32:17 > 0:32:22This reception committee seems to decide which ants are allowed in

0:32:22 > 0:32:25during the colony's sleep phase, and which aren't.

0:32:26 > 0:32:29Foraging ants which were still out of the nest

0:32:29 > 0:32:33when the colony went into a sleep phase are turned away at the door,

0:32:33 > 0:32:35so their return doesn't wake the main group.

0:32:37 > 0:32:41Every indication is that these long periods of synchronised rest

0:32:41 > 0:32:43are very important for the ants,

0:32:43 > 0:32:45these periods of what we might describe as sleep.

0:32:45 > 0:32:49And the reason we think that the ants are giving us ample evidence

0:32:49 > 0:32:51of the importance of this

0:32:51 > 0:32:54is that they seem to have gone to a great deal of trouble

0:32:54 > 0:32:58to organise their societies in such a way that they can maximise

0:32:58 > 0:33:02the number of individuals that can be inactive at any one time.

0:33:02 > 0:33:04It really strongly implies to me

0:33:04 > 0:33:06that these patterns of activity and inactivity

0:33:06 > 0:33:08are really important to these societies,

0:33:08 > 0:33:10and they're structured to preserve

0:33:10 > 0:33:13what seems to be a sleep-like behaviour

0:33:13 > 0:33:15for the good of the whole society.

0:33:25 > 0:33:30One of the groups we're watching at the zoo is the flamingos.

0:33:30 > 0:33:32While they're less sociable than the ants,

0:33:32 > 0:33:35they still live in a flock and work together.

0:33:36 > 0:33:40At night, each bird exhibits a different level of awareness.

0:33:40 > 0:33:44Those on the outside of the flock will remain vigilant

0:33:44 > 0:33:46for the safety of the whole group.

0:33:49 > 0:33:52All right, we're taking an infrared camera into the flamingos.

0:33:52 > 0:33:54SCATTERED CALLS

0:33:54 > 0:33:57They are vocalising ever so slightly,

0:33:57 > 0:34:00but hopefully we should see the beginnings of their behaviours

0:34:00 > 0:34:05and their flock interactions that reflect who's sleeping,

0:34:05 > 0:34:07who stays awake, throughout the night.

0:34:18 > 0:34:22Now, during the day, the flamingos tend to stay further away

0:34:22 > 0:34:25on both of the banks here in this enclosure,

0:34:25 > 0:34:29and at night, slowly but surely, they all descend into the water.

0:34:31 > 0:34:33The flamingos, unlike the ants,

0:34:33 > 0:34:36share responsibility for sentry duty.

0:34:36 > 0:34:39The birds will take turns adopting that role

0:34:39 > 0:34:42so that no one bird is constantly deprived of deep sleep.

0:34:45 > 0:34:48Now, the flamingos, at the moment, are still all awake.

0:34:48 > 0:34:52But what's interesting is they are getting into the water

0:34:52 > 0:34:54and coming closer to the deeper part.

0:34:57 > 0:34:59We're going to leave them to it,

0:34:59 > 0:35:01and of course our cameras are trained on them,

0:35:01 > 0:35:04so we'll keep a close eye on them and see what happens later on.

0:35:07 > 0:35:11The other birds we're monitoring tonight are the penguins.

0:35:11 > 0:35:16In the wild they live together in a group called a waddle.

0:35:16 > 0:35:19And it's difficult to observe any penguins sleeping at all.

0:35:21 > 0:35:23They appear alert almost all of the time.

0:35:25 > 0:35:28Very few studies have been carried out on penguin sleep.

0:35:28 > 0:35:30We're going to take a closer look

0:35:30 > 0:35:32at one of the individuals from this group.

0:35:36 > 0:35:37For studying birds in the wild,

0:35:37 > 0:35:40Bryson uses what's called an accelerometer,

0:35:40 > 0:35:44a device which records the tiniest of movements.

0:35:45 > 0:35:47But he's never tried one on a penguin before.

0:35:53 > 0:35:56Attaching this accelerometer to an aquatic bird is a real challenge.

0:35:56 > 0:35:58I don't think anyone's ever tried it before.

0:35:58 > 0:36:01Because they have really small feathers, and they go in the water.

0:36:01 > 0:36:03So getting the tape to stick onto that

0:36:03 > 0:36:04is going to be almost impossible.

0:36:04 > 0:36:06But these guys actually have wing bands,

0:36:06 > 0:36:08which I think I can put tape around the wing band

0:36:08 > 0:36:10and attach that to the accelerometer,

0:36:10 > 0:36:11and the nice thing then

0:36:11 > 0:36:13is I can see whenever they're flapping their wings at all.

0:36:13 > 0:36:16So I can see if they go for a midnight swim, or jump in the water.

0:36:16 > 0:36:17Or if they're just immobile all night.

0:36:17 > 0:36:19It'll be nice to see what they're up to.

0:36:22 > 0:36:24Bryson needs to attach the accelerometer

0:36:24 > 0:36:27securely enough so that it doesn't fall off or get pecked off.

0:36:29 > 0:36:31And to get the best data from the penguin,

0:36:31 > 0:36:35he needs it to stay in place for 24 hours.

0:36:43 > 0:36:44OK.

0:36:44 > 0:36:46He is really calm.

0:36:59 > 0:37:01- All right.- All right?

0:37:02 > 0:37:03Looks good.

0:37:03 > 0:37:06I think that'll stay attached very nicely, it looks good.

0:37:06 > 0:37:08I only put one piece of tape, but I think that's enough.

0:37:08 > 0:37:11It's... Yeah, I think it should be fine.

0:37:18 > 0:37:21Bryson left the penguin to go about its business

0:37:21 > 0:37:24and came back the next day to retrieve the accelerometer.

0:37:26 > 0:37:28And so, for the first time,

0:37:28 > 0:37:31we can see exactly what a penguin gets up to overnight.

0:37:34 > 0:37:38Our penguin was active, to varying degrees, for seven hours.

0:37:39 > 0:37:42It had two periods of marked inactivity.

0:37:42 > 0:37:45One for two hours and the other for almost three.

0:37:47 > 0:37:50Penguins sleep sporadically, and it's clear from our cameras

0:37:50 > 0:37:53that they don't all sleep at the same time.

0:37:55 > 0:37:58As opposed to the flamingos, which adopt a very strict pattern

0:37:58 > 0:38:02while sleeping, the penguins seem to adopt a more scattered approach.

0:38:04 > 0:38:07With the vast majority of individuals remaining awake,

0:38:07 > 0:38:11and very few individuals grabbing sleep in short bouts.

0:38:15 > 0:38:19Tapirs are thought to live in small family groups in the wild.

0:38:21 > 0:38:24The four tapirs at the zoo tend to sleep at the same time,

0:38:24 > 0:38:26but only for short bursts.

0:38:30 > 0:38:34I'm taking a look at their enclosure to see what they're up to,

0:38:34 > 0:38:38but the only animal I can see is a capybara.

0:38:43 > 0:38:46- WHISPERS:- The tapirs can scare quite easily,

0:38:46 > 0:38:49in fact in the wild they always rush to water for safety

0:38:49 > 0:38:52whenever they feel threatened by predators.

0:38:52 > 0:38:56The last thing we want to do is scare them all if they're all asleep

0:38:56 > 0:38:59and feeling nice and safe indoors,

0:38:59 > 0:39:04but weirdly enough it's the capybara who happens to sleep with the tapirs

0:39:04 > 0:39:05who's come out for a look.

0:39:08 > 0:39:11They are the most unusual looking creatures, aren't they, really?

0:39:12 > 0:39:16If the tapirs are indeed asleep, which I'm sure they are,

0:39:16 > 0:39:19it's definitely a good idea not to disturb them

0:39:19 > 0:39:23because this is one of their phases of sleep.

0:39:23 > 0:39:25We want to get an idea of how long each phase lasts,

0:39:25 > 0:39:27how many there are per night,

0:39:27 > 0:39:29and that's part of the results we're looking for

0:39:29 > 0:39:31at the end of the evening - well, by dawn tomorrow.

0:39:31 > 0:39:35So maybe it's a good idea to just sneak out of here now

0:39:35 > 0:39:37before we wake them.

0:39:42 > 0:39:43Gently does it.

0:39:46 > 0:39:50Had we got too close, the tapirs would undoubtedly have woken.

0:39:51 > 0:39:54When asleep, an animal is less responsive

0:39:54 > 0:39:56and less aware of its environment,

0:39:56 > 0:39:59but still needs to be ready to wake in case of danger.

0:40:01 > 0:40:06This is all the more important for prey animals like the tapirs.

0:40:06 > 0:40:09So how do animals ensure they are getting enough sleep,

0:40:09 > 0:40:12and yet remain alert to danger?

0:40:15 > 0:40:19Meerkats are notoriously wary animals.

0:40:19 > 0:40:21When they're awake, they're very quick to react

0:40:21 > 0:40:22to the slightest danger.

0:40:24 > 0:40:28At Paradise Wildlife Park in Broxbourne, north of London,

0:40:28 > 0:40:31I want to test the meerkats' reactions to threats

0:40:31 > 0:40:32while they're asleep.

0:40:35 > 0:40:39Meerkats are known for being an extremely vigilant species,

0:40:39 > 0:40:42and in the wild, studies have shown that when they're foraging

0:40:42 > 0:40:44they can recognize different predator sounds

0:40:44 > 0:40:48and they can discern between different meerkat alarm calls.

0:40:48 > 0:40:50But what we're interested in tonight

0:40:50 > 0:40:54is whether these fellas can perceive auditory threats

0:40:54 > 0:40:56when sleeping.

0:40:56 > 0:40:57How deeply do they sleep,

0:40:57 > 0:41:00can they maintain a certain level of vigilance,

0:41:00 > 0:41:03and can they discriminate between different sounds?

0:41:03 > 0:41:06We'll find out, won't we?

0:41:08 > 0:41:13Meerkats may be nervous animals, but they're also extremely curious.

0:41:14 > 0:41:15Oh, my God,

0:41:15 > 0:41:18there's one inside my jacket going up my jumper...

0:41:23 > 0:41:25So, Jessie, how many in this mob?

0:41:25 > 0:41:28There's 16 in here, it's Mum, Dad and all their children.

0:41:28 > 0:41:31OK, dominant female, patriarch, all the siblings -

0:41:31 > 0:41:35and despite the fact that they are captive bred, and born,

0:41:35 > 0:41:39are they still an extremely vigilant, observant

0:41:39 > 0:41:41- type of animal here? - Yeah, definitely.

0:41:41 > 0:41:44I mean, we're in their inside enclosure at the moment,

0:41:44 > 0:41:45so they're not too worried,

0:41:45 > 0:41:48but when we're outside there's always at least one on sentry duty

0:41:48 > 0:41:50- looking out for birds of prey. - Just like in the wild.

0:41:50 > 0:41:53Yeah, I mean, they often think that the aeroplanes that go over

0:41:53 > 0:41:56are birds of prey so they'll respond to them just like they would.

0:41:56 > 0:41:58So when it comes to sleeping,

0:41:58 > 0:42:01this mimics as closely as possible a safe haven,

0:42:01 > 0:42:04like their burrows in the wild, and what we want to find out

0:42:04 > 0:42:07is whether, even in the realms of this safety,

0:42:07 > 0:42:12how they might sleep, how aware they might be of external auditory cues.

0:42:12 > 0:42:14So we'll have a little go at that and see what happens tonight.

0:42:14 > 0:42:16- Mm, great.- Excellent.

0:42:16 > 0:42:20We've set up cameras and speakers in the meerkats' nests,

0:42:20 > 0:42:23and our researcher is ready to play the sounds

0:42:23 > 0:42:26while we watch what's going on from a safe distance.

0:42:28 > 0:42:29While we've been gone,

0:42:29 > 0:42:33the meerkat gang have been settling into their favourite nest box,

0:42:33 > 0:42:34the smaller of the two.

0:42:37 > 0:42:40Right, well, that is unmistakably

0:42:40 > 0:42:42- the behind of a meerkat.- Yep.

0:42:42 > 0:42:44Would you say he's asleep?

0:42:44 > 0:42:46Yeah, you can see how sort of slow he's breathing.

0:42:46 > 0:42:49Right in front of the camera - which I'm not surprised about,

0:42:49 > 0:42:52I mean, there's - what? 16 of them all huddled up in that nest box?

0:42:52 > 0:42:55Yeah, 16 - that's the smaller nest box, so it is around that large.

0:42:55 > 0:42:57And they do like to sleep piled on top of each other,

0:42:57 > 0:42:59even in the wild to keep warm, don't they?

0:42:59 > 0:43:01Yep, I mean, they've got a bigger nest box in there,

0:43:01 > 0:43:05- but they always choose to sleep in the small one together, so...- Sweet.

0:43:05 > 0:43:07So, now we're going to begin our little experiment

0:43:07 > 0:43:09and we're going to play two different sounds,

0:43:09 > 0:43:11one is a neutral sound, the sound of wind,

0:43:11 > 0:43:14and another is the sound of a meerkat alarm call

0:43:14 > 0:43:17and we're going to play them at different volumes,

0:43:17 > 0:43:20starting with barely audible to louder and louder.

0:43:20 > 0:43:22And we've got a researcher positioned

0:43:22 > 0:43:24just inside the enclosure door

0:43:24 > 0:43:27and we're going to see whether there is any reaction from the meerkats.

0:43:27 > 0:43:30We should be able to see it, obviously, inside the nest box

0:43:30 > 0:43:31via this camera

0:43:31 > 0:43:33and perhaps even just outside in the indoor enclosure,

0:43:33 > 0:43:38maybe even in the outdoor enclosure if a meerkat really reacts to it

0:43:38 > 0:43:40quite drastically.

0:43:40 > 0:43:43OK, so I am going to speak to our researcher now.

0:43:43 > 0:43:45Ross, can you hear me, over?

0:43:45 > 0:43:47RADIO: 'Yep, I can hear you.'

0:43:47 > 0:43:49OK, we're ready to start with the experiments,

0:43:49 > 0:43:53so go ahead with the first neutral sound at the lowest setting.

0:43:53 > 0:43:55'OK, wind playing now.'

0:43:56 > 0:44:00The first sound level is similar to a light whisper,

0:44:00 > 0:44:03but each level will get progressively louder.

0:44:03 > 0:44:04WIND WHISTLES FAINTLY

0:44:05 > 0:44:07- It's quite exciting, really. - It is quite intense.

0:44:07 > 0:44:10Yeah, I know, it's intense! That's the right word!

0:44:12 > 0:44:13Is anyone going to shift?

0:44:15 > 0:44:17No reaction whatsoever.

0:44:17 > 0:44:18OK.

0:44:18 > 0:44:22Let's play the first meerkat alarm call

0:44:22 > 0:44:24at the same low level, thanks.

0:44:24 > 0:44:26'OK, no worries.'

0:44:27 > 0:44:29MEERKAT ALARM CALL

0:44:30 > 0:44:32'And finished.'

0:44:32 > 0:44:34Not a twitch, all fast asleep, well done.

0:44:36 > 0:44:39'The nest box is the safest place the meerkats can be.

0:44:39 > 0:44:42'So perhaps it's not so surprising

0:44:42 > 0:44:45'that the first three volume levels don't cause them to stir.'

0:44:47 > 0:44:51OK, Ross, ready for level four, the wind noise, please, thanks.

0:44:53 > 0:44:58WIND NOISES AT LOUDER VOLUME

0:44:59 > 0:45:01'And finished.'

0:45:01 > 0:45:03No reaction, no repositioning.

0:45:03 > 0:45:07OK, thanks, Ross, ready for meerkat alarm call, level four.

0:45:10 > 0:45:13MEERKAT ALARM AT LOUDER VOLUME

0:45:14 > 0:45:16'And finished.'

0:45:18 > 0:45:19Oh, oh, oh, oh!

0:45:27 > 0:45:29Ross, we have a meerkat outside the nest box,

0:45:29 > 0:45:31as far as we can see from the cameras.

0:45:31 > 0:45:33Just hold tight for one second.

0:45:35 > 0:45:37- Result!- This one is still fast asleep.

0:45:37 > 0:45:41This one does not care, he was not on duty tonight.

0:45:41 > 0:45:46That's really interesting, a meerkat left the nest box at our

0:45:46 > 0:45:51level four meerkat alarm call, went to investigate, is now back.

0:45:51 > 0:45:54He was only out there for a couple of seconds.

0:45:54 > 0:45:55Waking up the sleepyhead!

0:45:57 > 0:46:01I think it's definitely worth waiting for him to settle.

0:46:04 > 0:46:07The most beautiful close-up of a very, very sleepy meerkat.

0:46:07 > 0:46:10Look at that.

0:46:13 > 0:46:17OK, time to play our very last set of sounds, at the highest level,

0:46:17 > 0:46:19and see what happens.

0:46:20 > 0:46:22WIND NOISES AT EVEN LOUDER VOLUME

0:46:26 > 0:46:28And will they react to the noise?

0:46:28 > 0:46:29'And finished.'

0:46:29 > 0:46:30Let's give it a second.

0:46:33 > 0:46:35OK, Ross, go ahead and play

0:46:35 > 0:46:38the meerkat alarm call level five, thanks.

0:46:42 > 0:46:46MEERKAT ALARM AT EVEN LOUDER VOLUME

0:46:56 > 0:46:58Ooh, someone has left the box!

0:46:59 > 0:47:00A meerkat has left the box.

0:47:00 > 0:47:03Was it worth getting out of bed for? That's what they're thinking.

0:47:03 > 0:47:07Was it worth getting out of bed for? Exactly! Now, that...

0:47:07 > 0:47:09is interesting.

0:47:09 > 0:47:14On both of our alarm calls that were loud enough for them to hear it,

0:47:14 > 0:47:15a meerkat left the box,

0:47:15 > 0:47:18and a meerkat did not leave the box after the wind.

0:47:18 > 0:47:22Now, the wind may have disturbed them a wee bit, you know,

0:47:22 > 0:47:25we can't separate the two completely, but you know, this is

0:47:25 > 0:47:31definitely indicative of a very strong reaction to a foreign noise

0:47:31 > 0:47:35that isn't neutral, like something they've heard before.

0:47:35 > 0:47:39Coming back in to settle, heads and tails and bums

0:47:39 > 0:47:43and legs everywhere, in a beautiful meerkat huddle.

0:47:45 > 0:47:48The results of our little experiment show that animals have

0:47:48 > 0:47:51adapted to maintain a level of vigilance which allows them

0:47:51 > 0:47:55to distinguish between external stimuli, filtering sensory inputs

0:47:55 > 0:48:00into those which require action and those which don't.

0:48:00 > 0:48:05Therefore, at least partially reducing the risks posed by sleep.

0:48:08 > 0:48:11It's also clear that not all the meerkats reacted.

0:48:11 > 0:48:13During the day, there is always one meerkat

0:48:13 > 0:48:15on sentry duty, the job

0:48:15 > 0:48:19being shared on a rotation amongst the adults.

0:48:19 > 0:48:22It could be that the meerkats maintain this system

0:48:22 > 0:48:24even during sleep.

0:48:31 > 0:48:35We can see from our monitors that the lion cubs are now

0:48:35 > 0:48:38stirring, as we expected them to at some point during the night.

0:48:40 > 0:48:44Ketan's up and about and I'm going to take the infrared camera,

0:48:44 > 0:48:46to see what he gets up to.

0:48:52 > 0:48:55Here he comes. Here he comes.

0:48:58 > 0:48:59He's so curious.

0:49:00 > 0:49:02Probably wondering what on earth

0:49:02 > 0:49:06people are doing here at this time of night.

0:49:06 > 0:49:07This is highly unusual.

0:49:09 > 0:49:13I mean, although they can be active during the day,

0:49:13 > 0:49:17at night, lions sleep for a very long time every day.

0:49:17 > 0:49:20The thing is, they're carnivores. They're top predators.

0:49:20 > 0:49:22They get a lot of nutrition from their food.

0:49:24 > 0:49:26OK, let's go and try and see his brother.

0:49:34 > 0:49:36Ooh!

0:49:36 > 0:49:40Because I can't see him properly, it makes me slightly nervous.

0:49:42 > 0:49:44Wow, did you see that?

0:49:44 > 0:49:48'In the wild, adult lions will make use of the night to hunt,

0:49:48 > 0:49:52'but here, despite the hour, Kamran and Ketan can still

0:49:52 > 0:49:53'keep themselves occupied.'

0:49:55 > 0:49:57Look at them, look at them playing together.

0:49:58 > 0:50:00They're still big babies.

0:50:00 > 0:50:03Two lion cubs playing together in the dead of night.

0:50:08 > 0:50:12'Lions have adapted to catch up on sleep at any time,

0:50:12 > 0:50:16'so they can maximise their opportunities to hunt.

0:50:16 > 0:50:19'And we've already seen that ants guard their sleep closely.

0:50:19 > 0:50:23'Flamingos work together to ensure they get their sleep,

0:50:23 > 0:50:26'and meerkats seem to maintain a sentry system

0:50:26 > 0:50:28'throughout the night to protect their sleep.'

0:50:30 > 0:50:33We can see how important sleep is from all the behavioural

0:50:33 > 0:50:35adaptations associated with it,

0:50:35 > 0:50:39but also from the way animal anatomy has evolved to preserve it.

0:50:39 > 0:50:43So prey animals, like zebra for example, they need to be able to run

0:50:43 > 0:50:47away from predators, so like others in the equine family they've evolved

0:50:47 > 0:50:51a special musculoskeletal adaptation to be able to sleep standing up.

0:50:52 > 0:50:55We filmed three zebras at The Wild Place Project

0:50:55 > 0:50:57on the outskirts of Bristol.

0:50:58 > 0:51:01Members of the horse family, including zebra, can sleep

0:51:01 > 0:51:05while standing, by using what's known as the stay apparatus.

0:51:08 > 0:51:11We recorded zebras standing motionless for hours on end.

0:51:13 > 0:51:15The stay apparatus is a special mechanism

0:51:15 > 0:51:19that locks their shoulder and knee joints into place so that

0:51:19 > 0:51:23when they sleep, their upper bodies can relax into a sort of hammock

0:51:23 > 0:51:28shape, using significantly less energy than when standing normally.

0:51:28 > 0:51:32It's another example of the importance of preserving sleep

0:51:32 > 0:51:33in the face of danger,

0:51:33 > 0:51:37and how evolution has come up with physical adaptations to allow it.

0:51:41 > 0:51:45Now, this mechanism is made up of all these ligaments

0:51:45 > 0:51:47and tendons that stabilise

0:51:47 > 0:51:51all the joints in the leg, so that the leg is rigid

0:51:51 > 0:51:54and stable, with minimal muscular activity.

0:51:54 > 0:51:58Now, another animal with a great skeletal adaptation for sleep

0:51:58 > 0:52:02is the sloth, and Bryson has been studying these animals for 10 years.

0:52:05 > 0:52:07Bryson's research includes one of the few studies

0:52:07 > 0:52:09of sleep in wild animals,

0:52:09 > 0:52:11on an island off the coast of Panama.

0:52:13 > 0:52:16Using the latest technology to monitor sleep patterns

0:52:16 > 0:52:19in sloths, Bryson's uncovered important information

0:52:19 > 0:52:22about how these mysterious creatures sleep.

0:52:24 > 0:52:28Bryson, it's safe to say you know everything there is to know

0:52:28 > 0:52:31about these animals. Tell me about the skeletal adaption.

0:52:31 > 0:52:33So, the sloth is a strictly arboreal mammal,

0:52:33 > 0:52:36it can actually stand up on its legs, but as you can see from the

0:52:36 > 0:52:39skeleton here, they're perfectly adapted to hang from the trees.

0:52:39 > 0:52:41Now, unlike us, if I was to hang from a tree branch,

0:52:41 > 0:52:43I'd have to exert quite a bit of energy to hold on

0:52:43 > 0:52:47but the sloth actually requires energy to open its claws

0:52:47 > 0:52:51and let go, so it can hang here and not require any muscle.

0:52:51 > 0:52:52So what is it down to,

0:52:52 > 0:52:56ligaments and tendons doing the job of just locking everything to place?

0:52:56 > 0:52:58Not just that, but actually the bones in their hands

0:52:58 > 0:53:01and feet are designed in a way that actually allows them

0:53:01 > 0:53:04to lock in on the branch and just hang there, motionless.

0:53:06 > 0:53:09While the adaptations in the skeletons of the sloth

0:53:09 > 0:53:11and the zebra are relatively easy to see,

0:53:11 > 0:53:15the exact source of other sleep adaptations are more concealed.

0:53:16 > 0:53:19So, in a moment we're going to check out the seal enclosure

0:53:19 > 0:53:22to observe the zoo's only marine mammals,

0:53:22 > 0:53:27but first another marine mammal, the dolphin, has evolved a very specific

0:53:27 > 0:53:31and extraordinary adaptation which allows it to sleep while it swims.

0:53:34 > 0:53:38Some environments are hardly conducive to sleep.

0:53:38 > 0:53:41Marine mammals have their own unique problem to solve -

0:53:41 > 0:53:43how to sleep without drowning.

0:53:45 > 0:53:49Dolphins do have some physiological similarities to land mammals,

0:53:49 > 0:53:52but they spend their entire lives in the ocean.

0:53:54 > 0:53:58They have to surface to breathe, and although they can inhale and exhale

0:53:58 > 0:54:02in just a third of a second and they need to breathe far less often

0:54:02 > 0:54:06than a primate, typically they still need to do so between two and

0:54:06 > 0:54:09four times every minute. Without a very

0:54:09 > 0:54:13specific adaptation, they'd be unable to enjoy

0:54:13 > 0:54:15uninterrupted periods of rest.

0:54:19 > 0:54:21We visited Duisburg Zoo in Germany

0:54:21 > 0:54:24to see how dolphins tackle the sleep problem.

0:54:29 > 0:54:33Ulf Schonfeld has been looking after the dolphins here for 25 years.

0:54:38 > 0:54:42He's seen these dolphins sleeping, but not how you might expect.

0:54:46 > 0:54:51What we observe is when they are sleeping, they have one eye closed.

0:54:52 > 0:54:53If the calves are sleeping,

0:54:53 > 0:54:56they are swimming right underneath the mother,

0:54:56 > 0:54:59have the one eye open, look at the mother all the time

0:54:59 > 0:55:02and the other eye is closed.

0:55:02 > 0:55:06They do this for one or two rounds

0:55:06 > 0:55:08and then you see the baby is changing

0:55:08 > 0:55:11the position - open the other eye and close the other eye.

0:55:15 > 0:55:17To study what the dolphins get up to at night,

0:55:17 > 0:55:21we set up a sensitive low-light camera to monitor them.

0:55:22 > 0:55:24And here are the results.

0:55:26 > 0:55:30A dolphin passes the camera with its left eye closed.

0:55:33 > 0:55:36And a short while later, the same dolphin passes

0:55:36 > 0:55:39in the opposite direction with its right eye open.

0:55:41 > 0:55:43Jochen Reiter is Head Curator at the zoo,

0:55:43 > 0:55:47he can explain some of the science behind what we're seeing.

0:55:48 > 0:55:51The dolphins sleep with one eye open

0:55:51 > 0:55:54and the other one is closed.

0:55:54 > 0:55:58The eye that is open is opposite to the brain half

0:55:58 > 0:56:01that is sleeping, so quite a curious thing.

0:56:01 > 0:56:05It is what the scientists call unihemispherical sleep.

0:56:08 > 0:56:11In order to remain alert enough to continue breathing

0:56:11 > 0:56:15but also to be able to sleep, dolphin brains have evolved

0:56:15 > 0:56:17in such a way that one half can sleep

0:56:17 > 0:56:21while the other half remains awake.

0:56:21 > 0:56:25Unihemispheric sleep in mammals is extremely rare.

0:56:25 > 0:56:28It's thought to only occur in cetaceans like dolphins

0:56:28 > 0:56:30and whales, some seals, and manatees.

0:56:31 > 0:56:35There is a second point to the sleeping of dolphins,

0:56:35 > 0:56:40it's like they're resting in a sort of banana posture, you could say,

0:56:40 > 0:56:44with their head on the surface, maybe to left, to the right.

0:56:44 > 0:56:46It's hard to tell if one eye is open or is closed,

0:56:46 > 0:56:49but obviously those animals are resting,

0:56:49 > 0:56:50but they're not moving forward.

0:56:52 > 0:56:54During the night we filmed some instances of,

0:56:54 > 0:56:58as Jochen describes it, the "banana posture".

0:56:58 > 0:57:02Then later in the night, we caught something unexpected on camera.

0:57:03 > 0:57:07A dolphin appears to float along the surface on its side,

0:57:07 > 0:57:12go completely limp and drift down to the bottom of the pool -

0:57:12 > 0:57:15only coming back to when he hits the bottom.

0:57:19 > 0:57:23Bihemispheric sleep has never been unequivocally shown in dolphins.

0:57:23 > 0:57:26Could this be evidence that despite the risks,

0:57:26 > 0:57:29dolphins can exhibit bihemispheric sleep,

0:57:29 > 0:57:32both brain halves sleeping together?

0:57:34 > 0:57:38Dr Peter Evans lectures in marine mammal ecology

0:57:38 > 0:57:41at the University of Bangor in Wales.

0:57:46 > 0:57:50This here is a bottlenose dolphin with one eye shut,

0:57:50 > 0:57:55and it's typical of unihemispheric sleep that we observe

0:57:55 > 0:57:59not just in captive cetaceans, but we've observed in them in the wild.

0:58:01 > 0:58:05So, what we're seeing here is the bottlenose dolphin,

0:58:05 > 0:58:08relatively immobile and then it drops down

0:58:08 > 0:58:11below the surface and at that point it does look

0:58:11 > 0:58:14as though it may be engaged in bihemispheric sleep.

0:58:15 > 0:58:16So I would say that

0:58:16 > 0:58:19there's definitely unihemispheric sleep happening here.

0:58:19 > 0:58:22There could be bihemispheric sleep happening for a short

0:58:22 > 0:58:24period of time, a very short period of time.

0:58:26 > 0:58:29If the dolphins can sleep with one half of their brain

0:58:29 > 0:58:32and remain safe, why risk this

0:58:32 > 0:58:34seemingly dangerous bihemispheric sleep?

0:58:36 > 0:58:40The answer lies in REM, or rapid eye movement sleep,

0:58:40 > 0:58:46a very special type of sleep which can only happen bihemispherically.

0:58:46 > 0:58:49Until very recently it was thought that dolphins

0:58:49 > 0:58:53and whales did not engage in REM sleep, because they had never been

0:58:53 > 0:58:58observed carrying out anything that looked like bihemispheric sleep.

0:58:58 > 0:59:02But a very recent study has observed apparent bihemispheric sleep in

0:59:02 > 0:59:07sperm whales, when a pod was found motionless and unresponsive

0:59:07 > 0:59:10in the Pacific Ocean, floating in a vertical position,

0:59:10 > 0:59:14only waking up when a research boat accidentally

0:59:14 > 0:59:15bumped into one of the whales.

0:59:20 > 0:59:24There's only one species of marine mammal at Bristol Zoo.

0:59:24 > 0:59:27The South American fur seals.

0:59:27 > 0:59:31They sleep in the water, but of course, they can also sleep on land.

0:59:36 > 0:59:38Vicky is a senior presenter here at Bristol Zoo.

0:59:38 > 0:59:41Vicky, tell me about this pod, how many seals are there?

0:59:41 > 0:59:44We've got six South American fur seals altogether.

0:59:44 > 0:59:47We're a little bit of an unusual group - we have all males,

0:59:47 > 0:59:50and it's a little family unit, so we have Otari who's the dominant

0:59:50 > 0:59:53seal, he's the bull, and then we have his five sons with him.

0:59:53 > 0:59:55OK. Each with individual characters, I'm sure.

0:59:55 > 0:59:58Very, very different. It's brilliant to work with them.

0:59:58 > 1:00:01Lovely, and tell me about the dynamics of the pod,

1:00:01 > 1:00:03when they're active, when they're sleeping, how it works.

1:00:03 > 1:00:06During the day, especially in the summer months,

1:00:06 > 1:00:08we get the seals sleeping in the pool.

1:00:08 > 1:00:12They can look like a little synchronised swimming team.

1:00:12 > 1:00:14It's quite cute to see!

1:00:14 > 1:00:16And on land as well,

1:00:16 > 1:00:19generally evening times as we lock up the enclosure,

1:00:19 > 1:00:22they all start to position up on land, ready for a night's sleep.

1:00:22 > 1:00:24Would it be OK if we snuck up

1:00:24 > 1:00:26ever so slowly with our infrared cameras?

1:00:26 > 1:00:28- Of course, that would be brilliant. - Thank you.

1:00:28 > 1:00:30We're going to switch our cameras to infrared now,

1:00:30 > 1:00:32get as close as we possibly can without

1:00:32 > 1:00:35disturbing the seals, to get a look at what they're up to right now.

1:00:35 > 1:00:37Hopefully, they are asleep.

1:00:38 > 1:00:40OK, so we're ready to go into the seals now.

1:00:40 > 1:00:43We're going to be ever so quiet.

1:00:43 > 1:00:45We've got an infrared camera that's going to take the lead

1:00:45 > 1:00:49and I'm going to basically use the camera as my eyes.

1:00:49 > 1:00:50We're going to follow it in and see

1:00:50 > 1:00:53if we can spot the seals as they sleep.

1:00:53 > 1:00:54Here we go.

1:00:59 > 1:01:03OK. Now, this is where it gets a little bit tricky.

1:01:09 > 1:01:10Mind the step.

1:01:16 > 1:01:18Now, it's pitch black and we can't see a thing.

1:01:19 > 1:01:22We're going to use the monitor of the infrared camera

1:01:22 > 1:01:26to see where the dominant male is.

1:01:28 > 1:01:29You can hear them chuffing,

1:01:29 > 1:01:33and usually that's what the dominant seals do to the more

1:01:33 > 1:01:36subordinate ones, sort of to keep them in their place,

1:01:36 > 1:01:39and you can hear them doing it right now.

1:01:39 > 1:01:43What's interesting about fur seals' sleep is that not only do

1:01:43 > 1:01:47they sleep in a unihemispheric way, like our dolphins, but they

1:01:47 > 1:01:51also exhibit bihemispheric sleep when they're on land,

1:01:51 > 1:01:54and it's very similar to the sleep that we see in terrestrial mammals.

1:01:54 > 1:01:57So, when they're in the water, it's unihemispheric.

1:01:57 > 1:01:59When they're on land, it's bihemispheric.

1:01:59 > 1:02:04And some very interesting research has shown that when the seals

1:02:04 > 1:02:07are sleep-deprived, they will opt for bihemispheric sleep,

1:02:07 > 1:02:11and that indicates that bihemispheric sleep must have some

1:02:11 > 1:02:15critical role that unihemispheric sleep simply can't achieve.

1:02:16 > 1:02:17'On previous nights,

1:02:17 > 1:02:21'Otari, the dominant male, has been sleeping on his favoured rock.

1:02:23 > 1:02:26'But tonight, another male, Quito,

1:02:26 > 1:02:29'appears to have forced him from the top spot.

1:02:30 > 1:02:32'It's left the rest of the seals agitated.

1:02:32 > 1:02:35'They're in and out of the water.

1:02:35 > 1:02:38'It's this jostling for position that may be preventing

1:02:38 > 1:02:40'the seals from going to sleep,

1:02:40 > 1:02:43'but at the moment, Quito's defiantly staying put.'

1:02:46 > 1:02:48The seals are clearly aware of us right now,

1:02:48 > 1:02:51but it'll be very interesting to see how this dynamic shifts and changes

1:02:51 > 1:02:54as they settle down for a good night's sleep later on.

1:03:02 > 1:03:04Since making my way back to HQ,

1:03:04 > 1:03:07apparently it's all been kicking off in the enclosure.

1:03:07 > 1:03:11There's been a lot of vying for a very coveted spot on this rock

1:03:11 > 1:03:14over here, and there was a lot of sparring going on with

1:03:14 > 1:03:17some of the seals until Otari, the dominant male, had a proper

1:03:17 > 1:03:21growl at everybody and has calmed the situation down, I think.

1:03:23 > 1:03:27'But Otari is still not in his regular sleep spot.

1:03:27 > 1:03:31'The tussle has clearly disturbed the sleep of the entire pod.

1:03:32 > 1:03:34'But we mustn't let their fighting distract us

1:03:34 > 1:03:37'from the big questions here.

1:03:37 > 1:03:40'What's so important about REM sleep that the dolphins

1:03:40 > 1:03:44'and the sperm whales seemingly interrupt their unihemispheric sleep

1:03:44 > 1:03:49'to sleep with both halves of their brains engaged at the same time?

1:03:49 > 1:03:52'And why do the seals opt for bihemispheric sleep

1:03:52 > 1:03:53'when they need to?'

1:03:55 > 1:03:58Let's talk about non-REM sleep first. What exactly is it?

1:03:58 > 1:04:03So, non-REM sleep is non-rapid eye movement sleep and REM sleep is

1:04:03 > 1:04:06rapid eye movement sleep, and those are the two main big types of sleep.

1:04:06 > 1:04:09So non-REM sleep is what makes up the overall

1:04:09 > 1:04:11majority of the amount of time that we spend asleep,

1:04:11 > 1:04:14and humans, about 75% of the time is non-REM sleep.

1:04:14 > 1:04:18OK, and what is the function of non-REM sleep?

1:04:18 > 1:04:21So, non-REM sleep is thought to be the restorative kind sleep.

1:04:21 > 1:04:22So when you go to sleep and you wake up

1:04:22 > 1:04:26and feel refreshed, that's from slow-wave sleep or non-REM sleep.

1:04:26 > 1:04:28OK, and then REM sleep, what's that like?

1:04:28 > 1:04:32So, REM sleep is sort of the paradox, because generally you think

1:04:32 > 1:04:34when you're asleep, your mind is at ease

1:04:34 > 1:04:37and your brain is firing slower with these slow waves,

1:04:37 > 1:04:41but REM sleep, you have lots of low amplitude, high frequency waves.

1:04:41 > 1:04:44It's almost like your brain becomes real activated

1:04:44 > 1:04:46and it looks almost like your brain's awake,

1:04:46 > 1:04:49and this is when the majority of our dreams in humans occur.

1:04:49 > 1:04:53And during REM sleep, there's also this muscle atonia, what is that?

1:04:53 > 1:04:56So, your body basically paralyses itself during REM sleep

1:04:56 > 1:04:59and that's a good thing, because that's when we're dreaming

1:04:59 > 1:05:01and if your body didn't paralyse itself,

1:05:01 > 1:05:02you can act out your dreams.

1:05:02 > 1:05:05Has that been proven, that you can actually do that?

1:05:05 > 1:05:07It's actually a disorder called REM behaviour disorder

1:05:07 > 1:05:09and it's a very scary thing to have.

1:05:09 > 1:05:12People have to sleep in padded rooms and sometimes strapped down

1:05:12 > 1:05:14to their beds, because they'll get up in the middle of the night,

1:05:14 > 1:05:18dead asleep and act out their dreams and they can really hurt themselves.

1:05:18 > 1:05:20OK, interesting and worrying phenomenon.

1:05:20 > 1:05:24So, during REM sleep, humans are known to dream.

1:05:24 > 1:05:27The body paralyses itself so that humans don't act out

1:05:27 > 1:05:31their dreams, which I think is a fascinating phenomenon in itself.

1:05:31 > 1:05:34We know that some animals, some mammals and birds have

1:05:34 > 1:05:38REM sleep - does that mean that animals dream as well?

1:05:38 > 1:05:42Well, we're not really sure, the only way to study dreams systematically is to wake

1:05:42 > 1:05:45somebody up and ask them, so with an animal it's difficult to do that.

1:05:45 > 1:05:48However, we see this REM behaviour disorder in animals too, actually -

1:05:48 > 1:05:51in cats, they've shown this to happen.

1:05:51 > 1:05:53This is footage of a sleeping cat

1:05:53 > 1:05:56demonstrating REM behaviour disorder.

1:05:56 > 1:05:59It appears to be pouncing on prey.

1:05:59 > 1:06:04Cats have also been known to hiss as if challenging a threat when asleep.

1:06:04 > 1:06:06We're not 100% sure if they're acting out their true dreams.

1:06:06 > 1:06:09But it's the same phenomenon that we see in humans as in cats.

1:06:09 > 1:06:13Even in animals without REM behaviour disorder,

1:06:13 > 1:06:17the paralysis during sleep can be incomplete, which is why

1:06:17 > 1:06:20one of the characteristics of REM sleep is twitching.

1:06:22 > 1:06:26This is most easily observable at the zoo in the larger mammals -

1:06:26 > 1:06:29the lions, gorillas and tapirs.

1:06:33 > 1:06:36Bryson, you and your team are looking at the evolution

1:06:36 > 1:06:40of sleep. When it comes to REM sleep in particular, where are we so far?

1:06:40 > 1:06:43Well, scientists have shown that we see REM sleep in both birds

1:06:43 > 1:06:46and mammals, but to date, we haven't really found anywhere else

1:06:46 > 1:06:48in the tree of life.

1:06:48 > 1:06:51However, though, if we try to find out where REM sleep first

1:06:51 > 1:06:53originated, if we trace back both mammals

1:06:53 > 1:06:55and birds, the earliest ancestors

1:06:55 > 1:06:57then will be 300 million years ago

1:06:57 > 1:07:00and none of the species in between show REM sleep.

1:07:00 > 1:07:03So, we're not really sure at what point REM sleep started.

1:07:03 > 1:07:05So we know we've got REM sleep in mammals here,

1:07:05 > 1:07:06we know we've got it in birds here.

1:07:06 > 1:07:09Do we know for sure it's definitely not in reptiles?

1:07:09 > 1:07:11We haven't seen any indication to date of it

1:07:11 > 1:07:14being in any of these in-between animals.

1:07:14 > 1:07:16OK, so how do we go about finding out how it

1:07:16 > 1:07:20made its way into the mammal lineage and into the bird lineage?

1:07:20 > 1:07:23Well, what we're trying to do now is look at the most basal forms

1:07:23 > 1:07:25of these lineages to see if they also have REM sleep.

1:07:25 > 1:07:29OK, and by basal forms you mean the most ancient group of birds

1:07:29 > 1:07:31or mammals that are alive today?

1:07:31 > 1:07:33Exactly, and in the case of birds

1:07:33 > 1:07:34that would be birds like the ostriches,

1:07:34 > 1:07:37so we've done some studies and look and see if they have REM sleep

1:07:37 > 1:07:40as well, and we found some very interesting results.

1:07:40 > 1:07:41OK, so interesting, in fact,

1:07:41 > 1:07:45that we decided to recreate it in a farm in Bristol.

1:07:47 > 1:07:50As the most primitive living bird of its group,

1:07:50 > 1:07:53the ostrich has remained virtually unchanged for

1:07:53 > 1:07:5850 million years, which in the study of evolutionary biology

1:07:58 > 1:08:00makes it very interesting.

1:08:02 > 1:08:05So, we've come to St Swithun's Lodge on a beautiful winter's day

1:08:05 > 1:08:06to meet Paul Cook here.

1:08:06 > 1:08:09You've been keeping ostriches for over 20 years, is that right?

1:08:09 > 1:08:12- At least 20 years. - And how did you get into it?

1:08:12 > 1:08:15I was at the Royal Welsh Show in Malvern

1:08:15 > 1:08:18and decided that they looked nice in the back garden, as you do!

1:08:18 > 1:08:19So where do they sleep?

1:08:19 > 1:08:21- They've got a house just down here. - In that shed?

1:08:21 > 1:08:24- Yeah, in the shed. - So, is it OK if we set that place up

1:08:24 > 1:08:26- full of CCTV cameras...- Wow.

1:08:26 > 1:08:29..so we can have a proper look at the changes in their behaviour

1:08:29 > 1:08:31as they're sleeping? You can have a proper look as well. Yeah?

1:08:31 > 1:08:36Be the first time I've managed to get that close without waking them up.

1:08:36 > 1:08:40'For us to have a real look at what's going on with Paul's ostriches,

1:08:40 > 1:08:42'we've brought along an array of infrared cameras

1:08:42 > 1:08:44'to set up in his barn.'

1:08:44 > 1:08:47- Mind the step.- Thanks. - And the second one.

1:08:47 > 1:08:50OK, so this is it. The sleeping quarters.

1:08:50 > 1:08:53So, we need to figure out where to put our cameras.

1:08:53 > 1:08:55- We've got four. Is that right, Bryson?- Yeah, exactly.

1:09:00 > 1:09:03It's easy to see how close a resemblance these ostriches

1:09:03 > 1:09:07bear to their dinosaur ancestors, in comparison to the more highly

1:09:07 > 1:09:09evolved birds that came after them.

1:09:09 > 1:09:11For one thing, they are very big animals.

1:09:11 > 1:09:13They can be as tall as 3m in height

1:09:13 > 1:09:16and they can weigh up to 150kg,

1:09:16 > 1:09:18and if you get a look at their feet...

1:09:18 > 1:09:21I mean, they're enormous as well and they look suspiciously

1:09:21 > 1:09:24like those of the theropod dinosaurs that they evolved from.

1:09:27 > 1:09:31With all the cameras in place and our monitors set up in the kitchen,

1:09:31 > 1:09:34Paul can now bring the ostriches into the barn.

1:09:39 > 1:09:42So, in ostriches, there's two types of sleep -

1:09:42 > 1:09:44there's slow-wave sleep and REM sleep.

1:09:44 > 1:09:46And when they're in slow-wave sleep, they're actually

1:09:46 > 1:09:49sitting there with their head motionless, but their eyes

1:09:49 > 1:09:52are open as if they're awake, but they're actually in slow-wave sleep.

1:09:52 > 1:09:55Now, during REM sleep, though, their eyes are going to close

1:09:55 > 1:09:58and they're going to lose muscle tone, and so, their head

1:09:58 > 1:10:01will start to droop down a little bit and sometimes it will actually hit the ground.

1:10:01 > 1:10:05So here, OK... If we watch her for a second, I think she might be getting ready

1:10:05 > 1:10:09to transition from slow-wave sleep into REM sleep.

1:10:09 > 1:10:11Almost goes to like looking slightly drunk, doesn't it?

1:10:11 > 1:10:14Exactly, here she goes, right there. So, now she's starting to go into

1:10:14 > 1:10:16REM sleep, you see her eyes were

1:10:16 > 1:10:20just starting to close a second ago, her head's starting to bob around.

1:10:20 > 1:10:22So, she's most likely in REM sleep right now

1:10:22 > 1:10:25and this is what they do. And then up, so the eye opens up

1:10:25 > 1:10:28and she goes back probably into slow-wave sleep again, and they can

1:10:28 > 1:10:31transition in and out of REM sleep and slow-wave sleep many times.

1:10:33 > 1:10:36Ostriches are one of the only species in which

1:10:36 > 1:10:40we can see this moment of transition between non-REM and REM sleep.

1:10:41 > 1:10:44Many animals can be observed twitching or exhibiting

1:10:44 > 1:10:47rapid eye movement while in REM sleep,

1:10:47 > 1:10:50but the transition between REM and non-REM

1:10:50 > 1:10:53is nowhere clearer than in ostriches.

1:10:53 > 1:10:57Scientists have now found that REM sleep in ostriches is in fact

1:10:57 > 1:10:59rather different to REM sleep in humans.

1:10:59 > 1:11:02When the ostrich eyes are closed, their brain is

1:11:02 > 1:11:05oscillating between both REM and non-REM.

1:11:05 > 1:11:09In a human, when you go to sleep, you either are in REM sleep or

1:11:09 > 1:11:11slow-wave sleep, there's no in between. Your brain switches,

1:11:11 > 1:11:14and it's a global phenomenon, it's your whole brain doing it.

1:11:14 > 1:11:17But in the ostrich, they actually have a mixture,

1:11:17 > 1:11:20and the only other animal this has ever been found in is

1:11:20 > 1:11:24the platypus, which is also a very basal, archaic species.

1:11:24 > 1:11:27So, what we're seeing here is maybe the earliest form of REM sleep.

1:11:27 > 1:11:32It's possible that this combined sleep state where non-REM

1:11:32 > 1:11:36and REM are not clearly defined was a precursor to

1:11:36 > 1:11:40the sort of distinct sleep phases we see in mammals and birds today.

1:11:40 > 1:11:44So, on the evolutionary tree in the species that came before the

1:11:44 > 1:11:48ostrich and before the platypus, it's likely there was no REM sleep,

1:11:48 > 1:11:51and in the species that evolved from the ostrich

1:11:51 > 1:11:56and from the platypus, REM developed into its own separate sleep state.

1:12:01 > 1:12:05So it seems that ostriches represent a very important junction point

1:12:05 > 1:12:08in the evolution of birds, where the two separate stages

1:12:08 > 1:12:12of sleep, non-REM and REM, hadn't quite separated yet.

1:12:12 > 1:12:15Now, what's really interesting is this same pattern

1:12:15 > 1:12:16of REM development seems to have

1:12:16 > 1:12:21occurred in a completely different lineage, this time in the mammals,

1:12:21 > 1:12:24with the junction point here being represented

1:12:24 > 1:12:26by the basal mammal, the platypus.

1:12:26 > 1:12:31Now, if REM development has occurred in two separate lineages like this,

1:12:31 > 1:12:35this implies convergent evolution, a trait that has evolved in two

1:12:35 > 1:12:39different groups, completely independently of each other,

1:12:39 > 1:12:42and that adds to the evidence that REM sleep must be hugely

1:12:42 > 1:12:47important for these two groups to have evolved it independently.

1:12:47 > 1:12:50Now, the very latest research also shows that REM sleep may have

1:12:50 > 1:12:55evolved again in another lineage, this time in the cephalopods,

1:12:55 > 1:12:57the groups of octopuses and squids.

1:13:02 > 1:13:05Studying sleep in cephalopods is a very new line

1:13:05 > 1:13:08of research in animal sleep science.

1:13:08 > 1:13:11REM-like behaviours have been observed in cuttlefish,

1:13:11 > 1:13:14which include distinct sleep phases,

1:13:14 > 1:13:18changes in colour not related to camouflage function

1:13:18 > 1:13:21and thought to be synchronised with REM,

1:13:21 > 1:13:23rapid eye movements and twitching.

1:13:23 > 1:13:27I want to know if other members of the cephalopod family

1:13:27 > 1:13:29may show the same behaviour.

1:13:29 > 1:13:33Bristol Aquarium is home to a very special cephalopod,

1:13:33 > 1:13:35a giant Pacific octopus called Priscilla,

1:13:35 > 1:13:39and the staff here are convinced she dreams.

1:13:39 > 1:13:41Paul, when it comes to their personalities,

1:13:41 > 1:13:44because you've worked with different octopuses in your career,

1:13:44 > 1:13:47- they all have their own characters, would you say?- I would say so, yeah.

1:13:47 > 1:13:50Each octopus has its own personality.

1:13:50 > 1:13:52Our lovely girl here is a bit of a diva.

1:13:52 > 1:13:55She does like to think that she rules the aquarium,

1:13:55 > 1:13:57but you get octopus that are a little bit shy

1:13:57 > 1:13:59and tentative to start off with and you do get ones that just

1:13:59 > 1:14:02want to play, they want to interact, they love human interaction.

1:14:02 > 1:14:05OK, and they do have a reputation for being incredibly intelligent

1:14:05 > 1:14:07invertebrates, tell me a little bit about her.

1:14:07 > 1:14:09Well, we reckon she's just as intelligent

1:14:09 > 1:14:11as a three-year-old child. They love to play,

1:14:11 > 1:14:14they can be taught to do lots of different things.

1:14:14 > 1:14:16She is actually able to open jars without any issues.

1:14:16 > 1:14:20OK, wonderful, so, have you seen Priscilla sleep?

1:14:20 > 1:14:22We believe so.

1:14:22 > 1:14:24She does like to sit in certain places in the tank,

1:14:24 > 1:14:26she will colour-change quite happily.

1:14:26 > 1:14:28We can just see these tiny movements around the tips of her arms

1:14:28 > 1:14:31as well, which would suggest that she's dreaming of some sort.

1:14:33 > 1:14:36'Paul is going to feed Priscilla, and once she's been fed,

1:14:36 > 1:14:39'she should go to her favourite place on the side of the tank

1:14:39 > 1:14:41'and settle down to sleep.'

1:14:43 > 1:14:46So, when it comes to her sleeping patterns here at the aquarium,

1:14:46 > 1:14:50does she sleep... Ooh, ooh, oh, my God, she's actually pulling me up!

1:14:50 > 1:14:52Has she got hold of you?

1:14:52 > 1:14:56That's amazing. Does she sleep throughout the day and night?

1:14:56 > 1:14:59In little phases? How does it work?

1:14:59 > 1:15:01I'd say she probably has small catnaps,

1:15:01 > 1:15:04is probably the best way to describe it.

1:15:04 > 1:15:07So, we will find her sleeping first thing in the morning,

1:15:07 > 1:15:09you'll find her sleeping at night as well.

1:15:09 > 1:15:14- So, what we'll do, we've got our crab in the jar.- OK.

1:15:14 > 1:15:17This is just another example of how

1:15:17 > 1:15:19intelligent these animals are.

1:15:19 > 1:15:23A closed jar with a crab in it, and apparently

1:15:23 > 1:15:25Priscilla makes very light work of this.

1:15:28 > 1:15:31There we go, so you can see she's going to basically engulf

1:15:31 > 1:15:34that jar with her body, bring it into the mouth.

1:15:34 > 1:15:38Yep, yep, it's already positioned to the mouth.

1:15:38 > 1:15:40All she's got to do is remember how to undo the lid.

1:15:40 > 1:15:42Look at that.

1:15:42 > 1:15:46So, this is a good game for her. They'll actually...

1:15:46 > 1:15:48- The jar's off, by the way. - There we go.

1:15:48 > 1:15:50So, you can see the lid's already taken off,

1:15:50 > 1:15:53so she'll be reaching inside the jar. There she goes.

1:15:53 > 1:15:54Arm in the jar.

1:15:54 > 1:15:57So she'll reach deep inside there, grab the crab

1:15:57 > 1:15:58and she'll flick it up into her beak.

1:15:58 > 1:16:01Well, that's the end of the crab, there's dinner, done.

1:16:01 > 1:16:03Oh, my gosh, smooth as, so quick.

1:16:03 > 1:16:05Very, very quick.

1:16:05 > 1:16:07I can't believe how quickly that happened

1:16:07 > 1:16:11and how neatly the whole operation was carried out.

1:16:12 > 1:16:18OK, nice big meal now,

1:16:18 > 1:16:21and if we're lucky, she might just cuddle up for a little bit of a nap.

1:16:25 > 1:16:28'To find a common ancestor between mammals

1:16:28 > 1:16:33'and cephalopods, you have to go back 600 million years.

1:16:33 > 1:16:36'Octopuses are blue-blooded invertebrates

1:16:36 > 1:16:38'with a horny beak for a mouth.

1:16:38 > 1:16:41'Their nervous system and brains are very different to those of

1:16:41 > 1:16:45'mammals, with the main part of the brain surrounding their oesophagus.

1:16:47 > 1:16:50'Scientists have shown that they are remarkably intelligent,

1:16:50 > 1:16:55'but have they, like higher mammals and birds, developed REM sleep?

1:16:58 > 1:17:02'We put a camera in Priscilla's tank to see what happens at night.

1:17:02 > 1:17:06'At first, she's still very active.

1:17:06 > 1:17:10'Then she moves to her favoured sleeping position at the top

1:17:10 > 1:17:14'of the tank, where she remains motionless for several hours.

1:17:14 > 1:17:18'Are there any small twitches on the end of her tentacles?

1:17:18 > 1:17:21'Is her mantle changing colour rhythmically in a way

1:17:21 > 1:17:24'that isn't connecting to any external stimuli?

1:17:24 > 1:17:27'It's difficult to say. At present,

1:17:27 > 1:17:30'theories on REM sleep in cephalopods

1:17:30 > 1:17:32'are based on observation alone.

1:17:32 > 1:17:35'But future detailed scientific research may prove

1:17:35 > 1:17:39'the convergent evolution of REM in a third, entirely separate

1:17:39 > 1:17:41'lineage of the phylogenetic tree.'

1:17:43 > 1:17:46So, Bryson, if we know that REM sleep began to separate out,

1:17:46 > 1:17:49round about here with the ostriches and round about here with

1:17:49 > 1:17:53the platypuses, if we were to look at more highly evolved birds

1:17:53 > 1:17:57like flamingos and more highly evolved mammals like gorillas,

1:17:57 > 1:18:02for example, could we say that, with the more advanced types

1:18:02 > 1:18:06of animals in the group, REM became more important and more separate?

1:18:06 > 1:18:09Well, that's a difficult thing to say, actually.

1:18:09 > 1:18:13It would be great if we could just draw these great conclusions with REM sleep and amounts of sleep

1:18:13 > 1:18:16and things like that, with really simple things like brain size or body size,

1:18:16 > 1:18:20but really, that just doesn't hold true when we examine sleep across species.

1:18:20 > 1:18:25So, if REM sleep can't be associated to higher cognitive capabilities,

1:18:25 > 1:18:29you know, bigger brains etc, what can we associate it to?

1:18:29 > 1:18:32One of the biggest things we can see right now is that sleep

1:18:32 > 1:18:35patterns in general are really associated with ecological

1:18:35 > 1:18:36pressure and ecological niches.

1:18:36 > 1:18:40But when it comes to REM, we still don't know quite how it works,

1:18:40 > 1:18:42or why it works in different animals, do we?

1:18:42 > 1:18:45No, not at all, it would be great if we could say it's linked

1:18:45 > 1:18:48directly to intelligence or this or that, but right now the data

1:18:48 > 1:18:50doesn't show that, so, we're not really sure.

1:18:50 > 1:18:53So, for sleep scientists, is REM sleep

1:18:53 > 1:18:56and its function sort of the Holy Grail of research right now?

1:18:56 > 1:18:58That would be the Nobel prize-winning question, if you

1:18:58 > 1:19:02could answer the actual purpose of REM sleep and how it developed.

1:19:05 > 1:19:09The function of sleep, and the function of REM sleep in particular,

1:19:09 > 1:19:13are the most pressing questions in current sleep research.

1:19:14 > 1:19:17Questions that Bryson and his colleagues

1:19:17 > 1:19:21at the Max Planck Institute for Ornithology are trying to answer.

1:19:23 > 1:19:27Located in the forests of Northern Bavaria,

1:19:27 > 1:19:30the institute is a world leader in unravelling

1:19:30 > 1:19:32the science of animal sleep.

1:19:36 > 1:19:40Scientists here are studying normal animal sleep patterns

1:19:40 > 1:19:42as well as sleep anomalies

1:19:42 > 1:19:44in animals that don't seem to sleep at all,

1:19:44 > 1:19:47or that sleep in unexpected patterns.

1:19:50 > 1:19:54They also hope to use a wind tunnel to find out how birds seem

1:19:54 > 1:19:58to forego sleep for days on end while undertaking huge migrations.

1:20:01 > 1:20:03And they've already managed to map

1:20:03 > 1:20:05the brain waves from a chicken egg embryo,

1:20:05 > 1:20:08proving not only that the embryo sleeps,

1:20:08 > 1:20:12but also that it has distinct REM and non-REM phases.

1:20:13 > 1:20:16Birds are particularly interesting to study.

1:20:16 > 1:20:19If we can determine what happened during evolution in the course

1:20:19 > 1:20:21of mammalian evolution

1:20:21 > 1:20:25and avian evolution that resulted in similar sleep states,

1:20:25 > 1:20:28this might provide us clues to the function of these states.

1:20:30 > 1:20:33Researchers are now looking at the gaps

1:20:33 > 1:20:35in the evolutionary timeline of sleep.

1:20:37 > 1:20:41One of the studies that we just initiated is to look at

1:20:41 > 1:20:43brain activity in sleeping crocodiles.

1:20:43 > 1:20:45Crocodiles are very interesting,

1:20:45 > 1:20:48because they're the closest living relative to birds.

1:20:48 > 1:20:53So, we're in the process of using high-density sensors to

1:20:53 > 1:20:57record brain activity throughout much of the crocodilian brain,

1:20:57 > 1:21:01to really rule out, are they different from birds,

1:21:01 > 1:21:04or are there some similarities that have been missed in the past?

1:21:04 > 1:21:09The results of these studies could ultimately help scientists

1:21:09 > 1:21:13further our understanding of human sleep, and to decipher

1:21:13 > 1:21:17some of the bigger mysteries of sleep in the entire animal kingdom.

1:21:23 > 1:21:26It is now 6:45 in the morning and from our monitors,

1:21:26 > 1:21:29we can see that a few of our animals are definitely

1:21:29 > 1:21:32stirring and waking up for the day.

1:21:32 > 1:21:34Because the sun is rising, I think it might be

1:21:34 > 1:21:36a nice idea to have a little final walk around the zoo,

1:21:36 > 1:21:39- check out our animals.- Definitely. - Let's do it.

1:21:43 > 1:21:46The results are in and we can now compare how our animals

1:21:46 > 1:21:49slept across the course of the night.

1:21:49 > 1:21:52So which animals slept the most and which slept the least?

1:21:53 > 1:21:56The top spots are taken by the gorillas and the lions,

1:21:56 > 1:22:00both sleeping for just over eight hours.

1:22:00 > 1:22:02And yet, these two animals clearly showed us

1:22:02 > 1:22:06the difference between monophasic and polyphasic sleep.

1:22:07 > 1:22:10When the lions woke in the middle of the night,

1:22:10 > 1:22:11they got up and played.

1:22:11 > 1:22:14But when the gorillas showed signs of stirring,

1:22:14 > 1:22:17as monophasic sleepers, they didn't leave their bed,

1:22:17 > 1:22:20and within a few minutes, they were asleep again.

1:22:22 > 1:22:25The gorillas woke at 7am, but right now

1:22:25 > 1:22:26the lions are still asleep.

1:22:29 > 1:22:31I think he's up there, right? Yep.

1:22:31 > 1:22:32Come on.

1:22:33 > 1:22:34Wake up!

1:22:36 > 1:22:38Ah, they're still totally passed out.

1:22:38 > 1:22:42They're being so lazy this morning, that's brilliant.

1:22:42 > 1:22:46The individual results from the seal enclosure reflect a restless night.

1:22:49 > 1:22:51Whilst Juan, the seal pup, slept

1:22:51 > 1:22:54for five hours and 50 minutes,

1:22:54 > 1:22:55Otari, the dominant male,

1:22:55 > 1:22:57only clocked up four hours

1:22:57 > 1:22:59and 20 minutes.

1:22:59 > 1:23:00In fact, it was the seals that

1:23:00 > 1:23:01demonstrated the most

1:23:01 > 1:23:04unexpected sleep behaviours.

1:23:04 > 1:23:07Having observed them on previous nights, we saw Otari,

1:23:07 > 1:23:10in his regular sleep position as the leader of the pod,

1:23:10 > 1:23:13obtaining the most undisturbed sleep.

1:23:15 > 1:23:18But it seems that the pod is undergoing a shift in hierarchy,

1:23:18 > 1:23:22with Quito mounting a challenge for Otari's position,

1:23:22 > 1:23:26and this jostling has affected the sleeping patterns

1:23:26 > 1:23:27of the entire group.

1:23:29 > 1:23:31This is, of course, where we came last night

1:23:31 > 1:23:36with our infrared cameras. Looks very different in daylight.

1:23:38 > 1:23:39There they are.

1:23:42 > 1:23:45You've had an eventful night, you guys.

1:23:45 > 1:23:47Hey.

1:23:47 > 1:23:50They certainly had different phases of sleep last night,

1:23:50 > 1:23:53there was a lot of sparring and vying for positions.

1:23:53 > 1:23:55Things are changing in this hierarchy, I think.

1:23:55 > 1:23:56A lot of politics going on here.

1:23:56 > 1:23:58A lot of politics.

1:23:59 > 1:24:02- They're following us.- Well!

1:24:02 > 1:24:03All of them are following us!

1:24:04 > 1:24:08You've gotten used to us now, hanging out with you at night-time.

1:24:08 > 1:24:11Literally every single one's right here.

1:24:11 > 1:24:12Ahh, sweet.

1:24:17 > 1:24:19Another surprise came with the next two animals

1:24:19 > 1:24:22in our sleep league table.

1:24:22 > 1:24:24Both are nocturnal animals, but the sloth

1:24:24 > 1:24:27and the red pandas slept for five hours and 30 minutes

1:24:27 > 1:24:31and four hours and 40 minutes respectively.

1:24:31 > 1:24:32The sloth was quite active,

1:24:32 > 1:24:35with six sleep-wake cycles throughout the night.

1:24:35 > 1:24:38As a polyphasic animal that gets up to 10 hours of sleep

1:24:38 > 1:24:42a day in the wild, perhaps this isn't too surprising.

1:24:43 > 1:24:46But the red panda entered the nest box at 20 past midnight

1:24:46 > 1:24:50and stayed there until almost 5am.

1:24:50 > 1:24:53This unusual activity may be down to the cold temperatures

1:24:53 > 1:24:54we saw last night.

1:24:58 > 1:25:01The temperature may also have affected the sleep patterns

1:25:01 > 1:25:03of the fruit bats, that slept

1:25:03 > 1:25:05for four-and-a-half hours.

1:25:06 > 1:25:08In winter, the bats prefer

1:25:08 > 1:25:10to spend their time indoors,

1:25:10 > 1:25:11where it's warmer.

1:25:11 > 1:25:15So it's possible that their reduced daily activity contributes

1:25:15 > 1:25:17to an increase in restlessness at night.

1:25:22 > 1:25:28Next the flamingos, which as a group slept for four hours and 20 minutes,

1:25:28 > 1:25:29although individuals

1:25:29 > 1:25:30may have clocked up more.

1:25:32 > 1:25:34These were closely followed by the tapirs,

1:25:34 > 1:25:37which averaged four hours of sleep across the night.

1:25:37 > 1:25:38The rest of the time,

1:25:38 > 1:25:40they were up and about, feeding.

1:25:43 > 1:25:45Unsurprisingly, the two capybaras

1:25:45 > 1:25:46which share the enclosure

1:25:46 > 1:25:48followed roughly the same sleep

1:25:48 > 1:25:50patterns, although we did see

1:25:50 > 1:25:52some movement from them

1:25:52 > 1:25:53in the middle of the night.

1:25:56 > 1:26:00And the animals which slept the least were the penguins.

1:26:00 > 1:26:02These birds averaged three hours

1:26:02 > 1:26:04and 30 minutes across the night.

1:26:14 > 1:26:17So, Bryson, it was quite a large undertaking,

1:26:17 > 1:26:21trying to obtain sleep patterns in all the animals in the zoo,

1:26:21 > 1:26:25but what can we conclude from some of our data, then?

1:26:25 > 1:26:27Well, we had a nice variety of species that we were

1:26:27 > 1:26:31observing tonight and generally speaking, the predators slept

1:26:31 > 1:26:34a lot longer and a lot deeper than the prey species.

1:26:34 > 1:26:35OK, so what does that tell us?

1:26:35 > 1:26:39Is it about more highly evolved animals like predators versus

1:26:39 > 1:26:41prey animals that may not be as highly evolved,

1:26:41 > 1:26:44or is it about ecology and its constraints?

1:26:44 > 1:26:46It's absolutely about the ecology

1:26:46 > 1:26:48and the niche that each individually species fills.

1:26:48 > 1:26:52We always like to think that humans are the most evolved species and

1:26:52 > 1:26:54we sleep the best, and it's not really true, each species is

1:26:54 > 1:26:58sleeping in its own individual way and that's perfect for that species.

1:26:58 > 1:27:02So, in the end, Bryson, is sleep utterly vital

1:27:02 > 1:27:04to all animals on the planet?

1:27:04 > 1:27:07It seems to be a crucial component of life.

1:27:07 > 1:27:09I mean, it's just something that's absolutely necessary

1:27:09 > 1:27:11for a species to succeed, and if you don't sleep,

1:27:11 > 1:27:14you'll die, and I can definitely feel the effects of not

1:27:14 > 1:27:17sleeping for a night, I'm not going to die but I feel totally wiped out.

1:27:17 > 1:27:18I know, you and me both!

1:27:20 > 1:27:24We've observed vast differences in the zoo animals' sleep patterns,

1:27:24 > 1:27:28but that doesn't mean that any one animal had a better or worse

1:27:28 > 1:27:31night's sleep than the other.

1:27:31 > 1:27:35For every environmental constraint, each species has evolved

1:27:35 > 1:27:38a way to still obtain all the benefits of sleep.

1:27:38 > 1:27:40The evolution of these varied

1:27:40 > 1:27:43sleep behaviours and how each animal manages

1:27:43 > 1:27:47to gain the benefits of sleep are both very important subjects

1:27:47 > 1:27:50in the future of sleep research.

1:27:50 > 1:27:54We still have so much to understand about the exact function

1:27:54 > 1:27:58of sleep and all of its adaptations across the animal kingdom,

1:27:58 > 1:28:02but one thing is clear, sleep is far more complex

1:28:02 > 1:28:05and profoundly important than we previously thought.

1:28:05 > 1:28:08Without it, we simply wouldn't have the huge diversity

1:28:08 > 1:28:12of life that we have on the planet today, with each species

1:28:12 > 1:28:15having developed its own specific sleep mechanism to become

1:28:15 > 1:28:20perfectly attuned to the ecological niche in which it thrives.