♪♪ [ Birds chirping ] ♪♪ ♪♪ NARRATOR: Primates.

♪♪ Countless faces... ♪♪ ...one extraordinary family.

♪♪ ♪♪ Right now, remarkable new discoveries are being made... HOBAITER: Right there.

♪♪ NARRATOR: ...about primates all over the planet.

DR. MITTERMEIER: Wow!

♪♪ NARRATOR: Today, over half of the world's primates are under threat.

WICH: ...are launching in about 30 seconds.

DR. MITTERMEIER: Our number-one objective is zero extinctions.

♪♪ NARRATOR: Only by truly understanding their lives can we safeguard the future... of the primates.

♪♪ ♪♪ [ Birds chirping ] ♪♪ NARRATOR: Primates are the ultimate social animal.

[ Chimpanzee grunting ] Living in groups, they need to communicate constantly.

[ Chimpanzee whines ] [ Chimpanzee barking ] [ Chimpanzee screeches ] None more so than chimpanzees.

♪♪ Now, ground-breaking research is revealing that chimps have a secret language!

♪♪ Cat Hobaiter has spent 13 years studying chimps in Budongo Forest, Uganda.

♪♪ HOBAITER: We know that chimpanzees are really vocal.

They're vocalizing all the time, but what I'm really interested in is a whole other system of communication they have, which is their gestures.

[ Both whispering ] NARRATOR: Gestures are a vital part of human communication -- we make them all the time.

But Cat is the first person to study how wild chimpanzees use them... and what they might mean.

HOBAITER: It's essentially like trying to decode almost alien communication 'cause you're really starting from scratch.

NARRATOR: She worked out a way to decipher this alien language.

The trick is to spot what stops a chimp from gesturing.

HOBAITER: If I desperately need a coffee, as I do most mornings, then if I'd asked you to pass it to me and you passed me a cup of water, then I would probably ask for coffee again.

If you passed me the decaf, I would definitely ask for the coffee again, and the one thing that will stop me from asking you for coffee is when you pass me the coffee.

So that, ultimately, gets us at what I meant, what I was trying to communicate to you, and we do exactly the same with the chimps.

NARRATOR: So, by looking at what happens before and after each gesture, Cat can interpret their meaning.

HOBAITER: This is Melissa, who's one of our female chimpanzees, and her little boy is currently up at the top of this tree, and then she gives this very obvious little hand raise.

Now, if that was a human -- we do that all the time, right?

Get some attention in class.

But, for the chimps, it actually means something very different.

So, chimpanzees give an arm raise when they want somebody else to move themselves, and, in this case, what she wants is her little boy to come down the tree so that they can move off and find a new feeding patch together.

♪♪ NARRATOR: It can take Cat hours and hours of watching the footage to spot and decode a gesture.

HOBAITER: We've got Jennie and her two young children, so James and Janet.

Jennie walks in front of James, and she looks back at him, and then, right there -- she just kind of shows the heel of her foot and kind of gives it a little wiggle, and this foot present gesture -- it's not a very obvious one, right?

♪♪ Once we'd seen it a few times, we actually worked out that what it means is, "Jump onboard, so that we can travel off together" -- sort of a piggyback gesture.

♪♪ NARRATOR: Cat soon discovered gestures are used in almost every aspect of chimpanzee life.

HOBAITER: We've got a big group of males on the ground here, and Mussa is gonna grab a couple of leaves off the nearest tree, pops them in his mouth, and he starts to tear them... [ Mussa leaf clipping ] ...and you can hear this very distinctive sort of "tsk, tsk, tsk" kind of noise when they do this.

It's called a leaf clip gesture.

[ Chimpanzee leaf clipping ] This is chimpanzee flirtation.

There is a female chimp who's just up the tree from him, and this is all about getting the girls' attention.

This is kind of a chimpanzee pickup line, [Chuckling] basically.

Starts to climb down, and, yep, that seems to have done the trick.

A little bit of chimpanzee action going on.

So, just as humans do with language, there are words that you don't use every day, so there are words that you might want to use on a special occasion or when you're meeting somebody for the first time, so we're still picking up these kind of new occasional really special gesture types.

NARRATOR: So far, Cat has decoded more than 80 distinct gestures.

♪♪ ♪♪ But some remain a mystery.

♪♪ Now Cat's research extends beyond the forests of Uganda.

And she's discovering there is even more to chimpanzee gestures.

♪♪ HOBAITER: We're looking at gestural communication in chimpanzees right across Africa.

♪♪ What we're starting to see is that the different groups of chimpanzees seem to share most of the same gestures, but there are subtle differences in how often they do it or quite how they do it.

[ Chimpanzees hooting ] It's more like having a different accent or a different dialect.

♪♪ NARRATOR: This is a crucial discovery.

♪♪ It supports the idea that different chimpanzee groups have distinct cultures.

[ Chimpanzee grunts ] [ Chimpanzee barking in distance ] [ Chimpanzee grunting ] HOBAITER: I am in a race against time to try and find out about these different cultures and the communication because we're losing so many different groups and populations of chimpanzees every day.

♪♪ When we're talking about conservation, it's not just about numbers -- it's about losing the characters and the cultures and the individuals.

♪♪ If you lose a whole community, that's a whole culture you'll never get back.

Imagining the forest without them, it wouldn't be -- it wouldn't be this forest.

Um, yeah.

It would be -- It would be incredibly sad to lose them.

♪♪ ♪♪ ♪♪ [ Wind rushing ] NARRATOR: Primates are not just one of the most social animals, they're also some of the most accomplished tool-users.

[ Macaque calls ] This is Koram Island, off Thailand's east coast -- home to beach-combing long-tailed macaques.

They've mastered the art of a particular type of tool use... ♪♪ ...using rocks to crack open shellfish.

♪♪ Amanda Tan has been observing this unusual behavior for 7 years.

DR. TAN: The tool use in macaques is really, really rare.

You find macaques all over Southeast Asia, but it's really only a few populations living out on islands that we see tool-use behaviors.

It is just a culture that's really unique only to some groups of macaques.

NARRATOR: Amanda discovered these monkeys use tools in two distinct ways.

DR. TAN: So, the monkey in front of me here is doing what we call axe hammering.

That's when they use the sharp point of the tool to crack open oysters that are stuck on rocks.

♪♪ They also crack open sea snails and clams and take a pound hammer to smash that open.

♪♪ NARRATOR: The choice of hammer and the ability to use it have to be learned.

♪♪ DR. TAN: The young ones will learn to use tools by staying really close to the tool-users, so, when they are really little, like that one, they stay really close to their mom, then that's when they get their first taste of seafood.

♪♪ NARRATOR: The beach monkeys seemed like such exceptional tool-users, Amanda wondered if their skills were unique... ♪♪ ...or if they were shared by neighboring troops.

♪♪ So she decided to carry out an experiment.

♪♪ Just inland, there's another group of macaques that also have access to a seafood-lined shore.

♪♪ DR. TAN: And so what I'm trying to do is just to put some blocks of oysters down with some stones that I have collected from the island and see if these monkeys know what to do with it.

♪♪ NARRATOR: Amanda wants to test for herself if these monkeys know how to use the stones as tools.

♪♪ It's not looking hopeful.

DR. TAN: He seemed to pick up the stone and just sniff it and not know what to do with it and walk off.

♪♪ NARRATOR: Despite having shellfish nearby, they don't seem to know they can use stones as tools to get to the food.

♪♪ It doesn't mean they can't eventually work it out for themselves.

But what would that take?

♪♪ DR. TAN: It's a bit of luck and then a bit of learning.

You need one of the monkeys to be an innovator, and this behavior will slowly spread throughout the group so they learn from each other.

It's sort of a tradition or a culture.

NARRATOR: So once one monkey learns how to use a tool, they'll all pick up the skill.

For this troop, it looks like learning to use tools could take some time.

♪♪ For the macaque groups that can use tools, life is easier... ♪♪ [ Macaque screeches ] ♪♪ ...but there's a twist to this tale.

♪♪ On Koram Island, Amanda has discovered that their highly developed skills are having some surprising consequences.

♪♪ By using tools, these macaques are able to target the largest, juiciest oysters.

♪♪ And they can devour as many as 40 a day.

♪♪ DR. TAN: We do see evidence that they are depleting the shellfish on the island.

So when we compare the shellfish here versus an island just next to us, we see that the shellfish here are less abundant and they're also smaller in size.

♪♪ NARRATOR: This is the first reported case of a tool-using animal -- other than ourselves -- overexploiting a natural resource.

DR. TAN: We know for sure that humans are depleting the natural resources on the planet, and we never really thought that any other animal was doing it, as well.

♪♪ NARRATOR: If these monkeys continue to overharvest their environment, the shellfish could disappear.

Ironically, this extraordinary tool-using behavior would then also disappear.

♪♪ When it comes to surprising new discoveries, secret language and skilled tool use are just the tip of the iceberg.

[ Bird calling ] ♪♪ In Brazil, researchers captured female bearded capuchins flirting... ♪♪ ...by throwing stones.

♪♪ After weeks of pursuing the alpha male, females catapult rocks at him in a bizarre last attempt to win him over.

♪♪ In central Africa, remote cameras filmed the first-ever shots of chimps pond-dipping... [ Chimps grunting ] ♪♪ ...for algae.

♪♪ During the harsh dry season, algae becomes a precious and succulent source of food.

♪♪ And in 2017, Chinese scientists discovered a brand-new primate, the Skywalker Hoolock gibbon... ...already one of the world's most endangered species.

♪♪ ♪♪ This vast and complex network of reed beds surrounds Madagascar's largest lake.

♪♪ Lac Alaotra spans an area larger than Los Angeles... ♪♪ ...and is home to a shy and elusive creature.

♪♪ The Lac Alaotra Gentle lemur is the only primate to live its entire life over water.

This marshland is the only place it can survive.

Malagasy conservationist Heri Andrianandrasana has dedicated his life to protecting these vulnerable lemurs.

But, out here, his problem is actually finding them.

DR. ANDRIANANDRASANA: We have 23,000 hectares of reed beds here, so most of them are not accessible, and that is a challenge.

NARRATOR: The reed beds might be huge... but they were once much bigger.

They are being cleared for fishing and rice farming on a massive scale.

♪♪ Heri wants to know how many lemurs are left and exactly where they are... so they can concentrate conservation efforts.

But in a canoe, it's a near impossible task, which is why he's enlisted the help of some cutting-edge technology.

It's being pioneered by Serge Wich, a conservationist with a fascination for drones.

WICH: Drones can show us a visual image that is usually very strong and that helps to facilitate conservation.

NARRATOR: With him is a group of engineers, astrophysicists, and computer scientists -- all world experts in drone technology.

♪♪ They've used drones for everything from mapping archaeological sites to finding dolphins in the Amazon.

♪♪ Now they've come to Madagascar to see whether their custom-made drone can spot the lemurs.

♪♪ To have the best chance of detecting the secretive lemurs, they're using a powerful thermal camera.

[ Beeping ] It's very sensitive to body heat.

But the lemurs are so small, no one knows if the camera will be able to spot them in such a vast marshland.

They need to do a test.

WICH: Heri, I copy.

Over.

[ Beeps ] DR. ANDRIANANDRASANA: Hello, Serge.

I copy you.

NARRATOR: Heri guides the drone to where he knows there are definitely lemurs.

WICH: We are launching in about 30 seconds.

Over.

[ Beeps ] ♪♪ ♪♪ ♪♪ [ Beeps ] ♪♪ Heri, we're almost there.

I'm sure you hear it by now.

Over.

NARRATOR: Serge is flying blind and has no idea what the camera can see.

♪♪ Heri uses a handheld camera to capture a reference of the lemur's thermal fingerprint so they can compare.

♪♪ DR. ANDRIANANDRASANA: We are on our way back home.

Over.

♪♪ NARRATOR: It's only now that Serge will find out if the drone camera has really worked.

♪♪ ♪♪ ♪♪ WICH: You can quite clearly see three individuals, so three in a very tiny spot.

NARRATOR: These minuscule dots don't look like much, until they're matched with the images from the canoe.

WICH: Even though it's quite small, you see it fairly clearly -- you even see its tail a little bit, so we are sure it's a lemur.

♪♪ To finally see results is incredible.

That's very helpful for us to develop a system in the future that will hopefully be able to detect the lemurs while we fly over them.

♪♪ NARRATOR: If the drone can survey the entire lake, Heri can focus efforts where the lemurs need it most.

♪♪ ♪♪ There's still a long way to go, but Serge and Heri have taken an important step to safeguard the future of the Lac Alaotra Gentle lemur.

♪♪ [ Whistle blows ] ♪♪ For some, a passion for primates knows no bounds.

And world-renowned primate conservationist Russell Mittermeier is obsessed.

♪♪ Now he's in Tanzania on a mission.

♪♪ After 50 years' experience, Russ has a unique perspective on primate conservation.

♪♪ And he's witnessed their numbers decline firsthand.

♪♪ DR. MITTERMEIER: Primates are in a pretty dire situation worldwide.

♪♪ More than 60% of all primates are considered either critically endangered, endangered, or vulnerable.

NARRATOR: But Russ believes there is at least one solution.

DR. MITTERMEIER: To me, ecotourism is perhaps the best tool that we have for ensuring the long-term survival of these animals in their natural habitats.

NARRATOR: When tourists visit wilderness areas in search of primates, they generate income that's put back into protecting the animals and their forests.

♪♪ Now in his 70th year, Russ wants to become the first person to see every kind of primate in the wild... inspiring others to follow in his footsteps.

DR. MITTERMEIER: My main objective here in Tanzania is to see the last of the 79 different types of primates that exist on the planet.

I'm here to see the kipunji, which is this very unusual monkey, and it was not described by science until 2005, so that's really quite remarkable.

NARRATOR: Scientists divide primates into 79 different categories known as "genera."

The kipunji is in a genera all of its own.

Restricted to just a few forest patches in Southern Tanzania, it is now considered to be one of the most endangered primates on earth.

♪♪ ♪♪ For Russ to find his final primate, he'll need local expertise.

♪♪ Noah Mpunga and Tim Davenport are from the Wildlife Conservation Society.

They were first to report the existence of the kipunji and now protect them and their forest home.

♪♪ ♪♪ MPUNGA: Hoody, hoody.

Welcome to the camp.

DAVENPORT: Welcome.

DR. MITTERMEIER: Thank you.

Finally, we're going to get to see kipunji, I hope.

MPUNGA: Yeah, exactly.

DR. MITTERMEIER: The weather's got to cooperate a little... NARRATOR: But shortly after arriving at their forest camp, things take a turn for the worse.

Severe and unseasonal rains soon make conditions in the forest treacherous and the kipunji much harder to find.

[ Insects chirping ] DR. MITTERMEIER: I'm very anxious to get out tomorrow.

I don't care if it's raining.

I don't care if it's muddy.

NARRATOR: Hopefully, conditions will improve by morning.

♪♪ [ Tent zipping ] Dawn, and it's not really much better, but Russ decides to risk it and get going... before the monkeys do.

To help them, local ranger Atu has been trying to keep track of the kipunji.

ATU: [ Speaks Swahili ] MPUNGA: She saw them yesterday.

DR. MITTERMEIER: Okay.

MPUNGA: It's like 2 kilometers from here.

DR. MITTERMEIER: 2 kilometers.

Okay.

So, presumably, they're still there 'cause it's still raining?

MPUNGA: Yeah, could be.

DR. MITTERMEIER: Hopefully.

DAVENPORT: We will see.

♪♪ NARRATOR: Russ has been waiting for this morning for years... ♪♪ ...but no sighting is guaranteed.

♪♪ DR. MITTERMEIER: 2.29 kilometers so far, but it's up and down, up and down.

♪♪ ♪♪ I can smell them.

NARRATOR: While the kipunji can move quickly through the open canopy, for Russ, the dense undergrowth is nearly impossible to navigate.

♪♪ ♪♪ DR. MITTERMEIER: Like most African monkeys, they're very good at hiding.

♪♪ [ Whispering ] Oh, wow!

♪♪ Whoa!

Cool.

Wow!

♪♪ Yes.

Number 79 -- good spot.

[ Chuckles ] Been working on that for 49 years.

[ Laughs ] ♪♪ [ Whispering ] Oh, yeah, yeah, yeah, yeah.

Look at him.

Wow!

♪♪ Funny face... funny-looking monkey.

♪♪ This feels great.

I mean, this morning, I had just about given up with all the rain.

But we got them.

♪♪ These trackers are amazing.

Really good.

This woman is fantastic.

♪♪ This is a really special animal.

DAVENPORT: [ Clears throat ] NARRATOR: Russ is the first person to see every type of primate, but he hopes he won't be the last.

♪♪ DR. MITTERMEIER: I like stimulating people to go to remote places and engage with the communities, benefit the local economies -- that's what it's all about.

♪♪ NARRATOR: Ecotourism and primate watching can provide a new income for local communities and an incentive to protect primates and their homes.

DR. MITTERMEIER: It's clearly demonstrating to local communities the importance of these intact forests and the key species that occur within them.

Our number-one objective is to maintain the current diversity of the order of primates -- zero extinctions.

If we can replicate models like this across the world, we can save these species from extinction.

♪♪ ♪♪ NARRATOR: Across the planet, dedicated people are going to great lengths to save the world's most endangered primates.

♪♪ This orphan chimpanzee's family was killed by poachers.

Now he's being evacuated by Virunga's anti-poaching unit... and transferred 400 miles to a primate rehabilitation center... ...a safe haven, where he'll be cared for alongside other orphans.

♪♪ In Guatemala, rescued spider monkeys are on their way back into the wild.

Many were originally kept as pets, requiring 5 years in rehabilitation.

♪♪ They're being released together, a whole new troop to boost the wild population.

[ Monkeys chittering ] ♪♪ In Brazil, cocoa plantations are providing a new home for endangered golden-headed lion tamarins.

Much of their natural forest is now gone, but they thrive here.

♪♪ Locals benefit from the new income... and help save tamarins, too.

♪♪ All over the world, the future of primates is increasingly in our hands... ♪♪ ...including these charismatic residents of Malaysia's Penang peninsula... ♪♪ ...dusky langurs.

♪♪ Their once pristine forests are now bisected by busy roads.

♪♪ ♪♪ To move through their territory, they must risk crossing dangerous traffic every day.

♪♪ ♪♪ Local researcher Jo Leen Yap has seen them run this gauntlet many times.

YAP: It's very risky, and you feel very heartache because the infants or the juveniles -- they will try to cross the road, and you can see that they are really struggling.

NARRATOR: The langurs have found what might appear to be a good solution... but these are power cables.

[ Langur screeches ] They pose a real risk of electrocution... and they're too thin for the monkeys to balance safely.

♪♪ Many struggle to make it across... especially mothers and babies.

YAP: When the mum and the infant try to cross along the cable wire, they can't really balance themselves well.

♪♪ ♪♪ ♪♪ [ Vehicles passing ] NARRATOR: Jo Leen felt she had to act.

YAP: After so many months and years of looking at them walking along the cable wire, the thing is in my heart is trying and help them to cross safely.

♪♪ NARRATOR: Jo Leen knows the monkeys prefer crossing overhead, so she's decided to install a monkey bridge.

YAP: So, today is the day -- we are going to build the first bridge in Peninsular Malaysia to assist langurs to cross the road.

NARRATOR: They are using upcycled old fire hoses, much thicker and easier to cross than electric wires... YAP: [ Speaks Malay ] NARRATOR: ...and hopefully allowing monkeys and other wildlife to cross between forest fragments much more safely.

♪♪ As the bridge nears completion, it seems the monkeys are already keen to check out their new walkway.

YAP: Stay here, stay here, stay here, stay here.

♪♪ So, it might take days or even weeks and months for them to get used to the fire hoses bridge.

So we just have to hope for the best.

♪♪ NARRATOR: Elsewhere, primate walkways have already been a great success.

In India, fire-hose ladders have been installed for lion-tailed macaques.

And in Thailand, gibbons take to new crossings with ease.

♪♪ Given time, it's hoped that these dusky langurs will soon be crossing safely, too.

♪♪ ♪♪ The passion people feel for primates is now perhaps their best hope for survival... ♪♪ ...especially for the world's last remaining mountain gorillas.

♪♪ ♪♪ [ Gorilla growls softly ] ♪♪ ♪♪ Their stronghold is the Virunga mountains.

♪♪ [ Gorilla snorting lightly ] ♪♪ Innocent Mburanumwe grew up here in the Democratic Republic of Congo.

He's now the deputy chief ranger of Virunga National Park, and he has a special bond with its gorillas.

MBURANUMWE: [ Smooching ] I love to spend time with gorillas -- you know, we consider them like our second families.

This is Nyakamwe, a silverback.

He's playing with his son, Balingene.

NARRATOR: Innocent has dedicated his life to these primates -- his fascination started at a young age.

MBURANUMWE: The first time I saw the gorillas, I was about 11.

What inspired me to become a ranger is because my father was a ranger, my brother and my uncle.

[ Gorillas grunting lightly ] ♪♪ NARRATOR: Now, Innocent is a world-leading authority on these gorillas and knows their lives intimately.

MBURANUMWE: He's just come to smell me.

Once he touch me, he just put his hand on his nose to smell.

[ Chuckles ] ♪♪ NARRATOR: These precious moments may seem idyllic... but in reality, being a ranger in the Virunga National Park is one of the most dangerous jobs in conservation.

[ Radio chatter ] ♪♪ [ All screaming ] The park is in one of the most politically unstable places on the planet.

REPORTER: 4 million people have been uprooted... REPORTER #2: Village after village destroyed by fighting... [ Child screams ] It's a battle for survival.

NARRATOR: In the last 20 years, conflict, militias, genocide, and Ebola have plagued the region.

For those protecting the park, the conflict is a direct threat.

REPORTER #3: The ongoing civil war and poaching have become the deadliest threats to the mountain gorillas.

♪♪ NARRATOR: In 2007, seven gorillas were gunned down.

♪♪ MBURANUMWE: It was a hard time to see gorillas being killed by people, like a sabotage.

♪♪ NARRATOR: And it's not just the gorillas that Innocent has had taken from him.

♪♪ [ Man shouts ] NARRATOR: Innocent's brother is one of more than 180 rangers who have been killed protecting the gorillas and Virunga Park itself.

[ Shouting continues ] ♪♪ ♪♪ The Virunga Park was founded primarily to protect mountain gorillas.

♪♪ But it has a role in bringing stability to the region.

♪♪ In recent years, tourists have returned, raising precious funds... allowing the park to create opportunities for local communities and to oversee the building of schools and clinics.

♪♪ And all of this helps to ensure the gorillas remain protected, too.

♪♪ In the 1980s, there were as few as 250 mountain gorillas in the Virunga region.

♪♪ After years of efforts to protect them, their numbers have climbed to about 880.

♪♪ But for Innocent and his team, the battle continues.

MBURANUMWE: I don't want to lose any gorillas.

I have to focus on my protecting these mountain gorillas because I love them.

♪♪ NARRATOR: The gorillas will need protecting for generations to come.

MBURANUMWE: I have one son who want to be a ranger like me.

♪♪ NARRATOR: The remarkable recovery of mountain gorillas is thanks to those who are willing to go to great lengths to protect primates.

♪♪ The conservation of the world's primates is a long-term commitment... in part because they live such long lives.

[ Birds chirping ] The rainforests of Indonesia are home... to orangutans.

♪♪ ♪♪ An infant orang can grow up to live for 50 years or more.

♪♪ They stay with their mothers up to the age of 9... ♪♪ ...learning all they need to survive.

♪♪ Today, all orangutans face an uncertain future.

♪♪ Since 2001, Indonesia has lost 35 thousand square miles of primary forest.

♪♪ Much went to satisfy the demands for timber, mining, and palm oil.

♪♪ The equivalent of 1,000 football fields are cleared every single day.

[ Birds chirping ] This destruction means that orangs are in serious need of help.

♪♪ Signe Preuschoft felt she had to help save them.

♪♪ ♪♪ These young orangs are orphans... being prepared for a life back in the wild.

♪♪ DR. PREUSCHOFT: So, in this -- in this Forest School program, we have a total at the moment of eight orangutans.

NARRATOR: Each vulnerable youngster has gone through the trauma of losing his or her mother.

DR. PREUSCHOFT: And this one here, Gerhana -- that's the youngest.

♪♪ In Gerhana's case, it was just amazing that he would live.

He was so starved, he looked like a stick insect.

♪♪ So it was really touch and go whether he would make it.

♪♪ NARRATOR: Since coming into the Forest School program, Gerhana, like the other rescued orphans here, has made a remarkable recovery.

♪♪ Each is cared for by a dedicated human surrogate parent.

♪♪ The long-term goal is to release them into protected forests and boost wild populations.

But rehabilitation can often fail.

DR. PREUSCHOFT: [ Speaking indistinctly ] NARRATOR: Many orangs do not survive in the wild after release.

♪♪ They often lack vital skills they would have learned from their mothers, high in the treetops.

♪♪ The canopy is where orangs find food, shelter, and safety from predators, and that's part of the problem.

♪♪ DR. PREUSCHOFT: There is always a big attraction for the orphans to come down to the ground.

So, as long as we have many caretakers on the ground, it's almost impossible to get the orangutans all up in the trees.

♪♪ NARRATOR: In the wild, orangutans rarely if ever come to the ground.

♪♪ Signe had an idea -- their caregivers would have to lead the way... into the trees.

♪♪ James Reed is a highly experienced professional tree climber.

REED: Okay, so, this is called the throw line, and this is called the throw pouch.

TRANSLATOR: [ Speaking native language ] Throw, lampah, throw.

NARRATOR: The idea -- if the carers can climb, then their orangs should follow.

REED: Once it starts swinging, lower it down.

There you go.

♪♪ NARRATOR: But some humans find it easier than others.

DR. PREUSCHOFT: [ Laughs ] I have too much rope now.

REED: No, it's okay.

DR. PREUSCHOFT: [ Speaking indistinctly ] REED: Yeah.

Too much is better than not enough.

That's it.

NARRATOR: Long training hours are needed to become certified climbers.

But the real test will come... when boisterous young orangs are added to the mix.

♪♪ ♪♪ ♪♪ REED: Good.

Here.

♪♪ NARRATOR: When the caregivers take to the ropes, even Gerhana, with a little encouragement, discovers he's a natural.

♪♪ ♪♪ Up here, they can really strengthen their skills... ...explore new heights... ...and discover new foods... ...with the safety of their caretaker nearby.

♪♪ Signe started seeing a promising change in the orphans right away.

♪♪ DR. PREUSCHOFT: When we first climbed with Gerhana, I had never seen Gerhana climb so high as on that day.

♪♪ NARRATOR: This is a positive first step towards these infants becoming truly at home in the canopy.

♪♪ DR. PREUSCHOFT: As soon as they don't need us, we just let them go as much as they want and give them the self-confidence -- "Okay, I can handle that."

♪♪ NARRATOR: Signe hopes she's giving these orangs the tools they need to survive... ♪♪ ...and that she can release them one day where they belong... in the wild.

♪♪ Primates... are our closest relatives.

They need us now more than ever.

♪♪ It's only by understanding them that we can safeguard their future.

♪♪ Across the world, people are dedicating their lives to finding the answers.

♪♪ ...and making sure the future always has a place... ♪♪ [ Animal chittering ] ...for the primates.

♪♪ ♪♪ ♪♪ ♪♪ To learn more about what you've seen on this "Nature" program, visit pbs.org.

♪♪ ♪♪