For a family of proboscis monkeys, reaching a new feeding ground means taking an enormous risk. Instead of simply walking through the forest, the group must leap from the trees into a river where crocodiles may be waiting below. The unusual behavior is one of the most remarkable examples of how animals adapt to dangerous environments, especially for a species that spends much of its life around the rivers and wetlands of Borneo.
The footage from BBC Earth follows a group of proboscis monkeys as they prepare to cross the Sekonyer River in Tanjung Puting National Park, Central Kalimantan, Indonesia. Their destination is valuable: fresh young leaves on the opposite side. But getting there requires a spectacular leap of faith.
The proboscis monkey is already one of the strangest-looking primates on Earth, famous for its oversized nose and reddish-brown coat. But its appearance is not the most surprising thing about this species.
Its swimming ability may be even more remarkable.
A Family Faces a Dangerous Crossing
The monkeys are moving through the forest when they reach the river.
Across the water lies a fresh supply of young leaves.
For the group, this means food.
But between the monkeys and the feeding ground is a stretch of water that may contain one of the most dangerous predators in their habitat: the crocodile.
The BBC Earth footage shows the animals gathering near the riverbank as they prepare to cross.
For a human watching from the outside, the obvious question is simple:
Why would these monkeys voluntarily jump into crocodile-filled water?
The answer is that they have evolved a remarkable way to survive it.
Why the Monkeys Need to Cross
Proboscis monkeys are strongly associated with riverine and coastal habitats.
They live in areas including mangroves, river forests and other wetlands across Borneo. The species is endemic to the island, meaning it occurs naturally nowhere else in the world.
Their diet consists largely of leaves, particularly young leaves, as well as other plant material.
That means the availability of food can influence where a troop needs to move.
Sometimes the best feeding area is on the other side of a river.
The monkeys have to make a decision.
Stay where they are.
Or cross.
The River Is Full of Danger
The river is not simply an obstacle.
It is also habitat for aquatic predators.
Crocodiles can detect activity in the water, and the monkeys’ splashes can potentially draw attention from predators nearby.
A recent analysis of the BBC footage noted that the monkeys’ splashes can carry considerable distances through the water, potentially alerting crocodiles to their presence.
That creates an extraordinary problem.
The monkeys need to move quickly.
But moving quickly creates noise.
And noise can reveal their location.
The Alpha Female Takes the Lead
The group approaches the riverbank.
One of the males appears hesitant.
He watches the water.
He does not immediately jump.
Then another monkey takes the initiative.
The alpha female moves first.
Her decision changes everything.
She leaps.
The rest of the group now has a route to follow.
The BBC footage shows this sequence as the troop begins its dangerous crossing.
The Leap Is Surprisingly Long
A proboscis monkey does not simply walk down into the river.
It often launches itself from a tree or riverbank.
The animal pushes away from the branch and extends its body before hitting the water.
This behavior reduces the amount of time spent swimming.
The shorter the swimming distance, the less exposure the monkey has to aquatic predators.
The New England Primate Conservancy notes that proboscis monkeys may deliberately leap long distances from elevated positions to minimize the distance they need to swim.
Splash!
The first monkey hits the water.
A huge splash erupts.
For a moment, the calm river disappears beneath a burst of movement.
Then the monkey begins swimming.
This is where the species reveals one of its most unusual adaptations.
Proboscis monkeys are excellent swimmers.
Proboscis Monkeys Are Remarkable Swimmers
Most primates are not known for regularly swimming across rivers.
Proboscis monkeys are an important exception.
Research and natural-history observations have documented their ability to swim and even dive underwater.
Their partially webbed hands and feet help them move efficiently through water.
The BBC Wildlife explanation of proboscis monkey swimming describes them as unusually aquatic primates capable of swimming underwater.
That ability can make the difference between reaching safety and becoming prey.
The Monkeys Have Webbed Feet
One of the most fascinating adaptations is hidden at the end of their limbs.
Proboscis monkeys have webbing between some of their fingers and toes.
That feature helps them paddle through water.
It is an unusual adaptation for a primate.
But for a monkey living beside rivers, it makes perfect sense.
The animal’s body is adapted not only for climbing through trees but also for crossing water.
The Group Moves Quickly
One by one, the monkeys make the jump.
Each animal has to commit.
There is no halfway point.
Once the monkey leaves the branch, it is airborne.
Then comes the splash.
Then the swim.
And finally the climb onto the opposite bank.
The entire crossing is a race against time.
The Crocodiles Are the Hidden Threat
The danger is difficult for viewers to see.
The water may look relatively calm.
That is exactly what makes crocodiles so dangerous.
A crocodile can remain mostly hidden below the surface while watching or sensing movement above.
For a monkey, the surface of the river may conceal the predator until it is too late.
The New England Primate Conservancy’s species profile notes that proboscis monkeys often live around waterways where crocodiles and other predators are present.
Why the Monkeys Don’t Simply Find Another Route
It may seem strange that the group would choose such a dangerous crossing.
But rivers are also natural barriers.
Going around them may require a much longer journey.
The monkeys may have limited options when searching for new feeding areas.
Their ability to swim gives them access to habitats that other tree-dwelling animals might struggle to reach.
In other words, the same river that creates danger can also provide opportunity.
The River Is Part of Their Habitat
Proboscis monkeys are not accidental visitors to the water.
They are closely associated with rivers, mangrove forests and wetlands.
The species’ dependence on these environments makes swimming an important part of its ecological strategy.
The river is therefore both a threat and a resource.
It provides water.
It shapes the forest.
It can offer escape routes.
And sometimes it separates the monkeys from their next meal.
Then a Male Hesitates
After several monkeys have crossed, one male remains behind.
He appears reluctant.
The river is dangerous.
The splashes are loud.
And there may be crocodiles below.
For a moment, the monkey seems unwilling to take the same risk as the others.
This hesitation creates tension in the group.
The others have already crossed.
But he remains on the original side.
The Family Cannot Wait Forever
The group has moved ahead.
The reluctant male eventually has to make his decision.
Staying behind means being separated from the troop.
Crossing means entering the dangerous water.
Finally, he commits.
He leaps.
The hesitation is over.
A Mother and Baby Remain
But the most vulnerable members of the group have not yet crossed.
A mother and her baby remain on the original bank.
This changes the stakes.
An adult monkey can swim strongly.
A tiny infant is another matter.
The baby cannot simply make an independent crossing.
It must depend entirely on its mother.
The Baby Clings On
The mother takes the leap.
Her baby clings tightly to her body.
This is one of the most remarkable moments in the footage.
The mother is swimming.
The baby is holding on.
Below them is a river where crocodiles may be present.
The infant has no control over the route.
Its survival depends on the mother.
The BBC footage emphasizes that the baby must cling tightly as its mother crosses.
A Mother and Baby in Mid-Air
The image is extraordinary.
The mother launches from the bank.
For a moment, both animals are suspended above the water.
The baby is pressed against her.
Then they hit the river.
A huge splash follows.
The mother immediately begins swimming.
The baby remains attached.
There is no opportunity to stop.
Why Carrying a Baby Makes the Crossing Harder
An adult proboscis monkey can control its own body during a jump and swim.
A mother carrying a baby has another challenge.
She must move through the water while supporting an infant.
The baby also changes her balance and movement.
Yet the species’ body structure and swimming ability make this possible.
The mother continues toward the opposite bank.
The Baby Has to Hold Tight
For the infant, the crossing is entirely passive.
It cannot paddle effectively enough to make the journey independently.
It must cling to its mother.
This is common in many primates: young offspring depend heavily on their mothers for transportation and protection.
But here, the transportation route is a crocodile-filled river.
The stakes are unusually high.
A Remarkable Family Strategy
The crossing demonstrates something important about proboscis monkey family groups.
The adults are not simply moving individually.
They are moving as a group.
The more experienced individuals can lead.
The young follow.
And mothers transport their infants.
This allows the troop to reach new areas while protecting its most vulnerable members.
The Monkeys Are Better Swimmers Than They Look
Their unusual noses often dominate photographs of proboscis monkeys.
But their aquatic abilities deserve just as much attention.
Professor Ben Garrod’s Discover Wildlife explanation of primate swimming identifies proboscis monkeys as one of the rare primates that regularly swim and dive.
They can swim underwater and use their webbed hands and feet to propel themselves.
That is extraordinary for an animal that spends so much time in trees.
They Can Even Dive
Swimming is not the only aquatic skill these monkeys possess.
They can also dive beneath the surface.
Discover Wildlife reports that proboscis monkeys can swim underwater, with observations of them traveling below the surface.
That ability could potentially help them escape predators or navigate waterways.
It also shows how deeply adapted they are to life around water.
A Strange-Looking Monkey With a Special Adaptation
The proboscis monkey’s huge nose is its most famous feature.
Adult males have particularly large noses, while females have smaller ones.
Scientists have proposed several possible functions for the male’s nose, including roles in vocal communication and sexual selection.
But the animal’s unusual appearance should not distract from its broader adaptations.
It is a monkey built for life in the trees and around water.
Borneo Is Full of Unique Wildlife
Borneo is one of the world’s most biologically distinctive islands.
Its forests are home to species found nowhere else.
Proboscis monkeys are one example.
Orangutans are another.
The island’s isolated evolutionary history has produced an extraordinary collection of wildlife.
The BBC’s Earth’s Tropical Islands series emphasizes how island ecosystems can develop distinctive species and behaviors.
Why Island Life Creates Special Challenges
Island species often face unusual ecological pressures.
They may have limited habitats.
They may be isolated from populations elsewhere.
And they may depend heavily on specific ecosystems.
For proboscis monkeys, the loss or fragmentation of riverine and mangrove forests can reduce the habitat available to them.
That makes habitat conservation particularly important.
The Importance of Mangroves and River Forests
Proboscis monkeys are closely associated with coastal forests, mangroves and river systems.
These habitats provide:
- Food
- Sleeping sites
- Travel routes
- Water
- Escape options
- Places for social groups to gather
Protecting the monkeys therefore requires protecting the ecosystems they depend on.
The World Land Trust’s proboscis monkey information also highlights the species’ dependence on Borneo’s forested wetlands.
The River Is Both Highway and Hazard
For this family group, the river has two completely different roles.
It is an obstacle.
But it is also part of the landscape they have evolved to navigate.
The monkeys know how to cross.
They know how to leap.
They know how to swim.
They can even dive.
Yet they still have to respect the predators living beneath the surface.
Why Jump Instead of Entering Slowly?
A slow descent into the water would keep the monkey exposed for longer.
A leap reduces the time between leaving the tree and reaching the opposite bank.
The New England Primate Conservancy notes that proboscis monkeys may leap from considerable heights and aim for longer jumps to reduce the amount of swimming required.
It is a simple strategy with an important benefit.
Get across quickly.
But Jumping Creates a Splash
There is a trade-off.
A long jump may reduce swimming time.
But landing in the water creates a huge splash.
That splash can travel through the river.
And a crocodile may notice movement or disturbance.
The monkeys therefore have to balance two risks:
Spend longer in the water—or make a louder entrance.
Neither option is perfect.
The Group Has No Choice but to Continue
Once the first monkey jumps, the others have to follow.
The group has committed to the crossing.
There is no turning back for the animals already swimming.
Each monkey makes its own leap.
Each one hopes to reach the opposite bank.
One by One, They Make It
The crossings continue.
Adult monkeys hit the water and swim.
Some move quickly toward the opposite bank.
The group gradually gathers on the far side.
But the mother and baby remain the most worrying pair.
They still have to make the leap.
The Most Vulnerable Members Cross Last
This is one of the most tense aspects of the sequence.
The strongest or most confident animals have already crossed.
The vulnerable members remain.
The baby cannot choose the route.
It cannot swim independently.
It cannot escape a crocodile on its own.
The mother has to carry the responsibility.
The Mother Makes the Leap
Finally, the mother jumps.
Her baby clings tightly.
They hit the water.
The mother swims.
The baby remains attached.
And then they reach safety.
The crossing is complete.
The Whole Family Makes It
The final sequence shows the family group reunited on the opposite side.
Even the vulnerable baby has made it across.
The immediate danger is over.
For now.
The group can continue toward the young leaves that attracted them to the crossing in the first place.
A Dangerous Journey for Food
The entire crossing exists because the monkeys need resources.
The fresh leaves on the opposite bank provide a feeding opportunity.
That means the risk is connected directly to survival.
Animals cannot avoid every danger.
Sometimes food requires taking a risk.
The proboscis monkeys have evolved behaviors that make that risk manageable.
Why Proboscis Monkeys Are So Good at Swimming
Their swimming ability is not simply a lucky trait.
It is closely related to their ecology.
They spend much of their lives near rivers and wetlands.
They encounter water regularly.
They have evolved physical features that make aquatic movement easier.
Their webbed hands and feet provide propulsion.
Their ability to dive gives them another option.
And their willingness to leap means they can cross water quickly.
A Monkey That Can Swim Underwater
Most people associate monkeys with trees.
Proboscis monkeys challenge that assumption.
They can leave the canopy, plunge into a river and swim.
They can even travel underwater.
Discover Wildlife reports that they can swim underwater with their eyes open and remain submerged for significant periods.
That makes them one of the most aquatic primates known.
Crocodiles Create Constant Pressure
The presence of crocodiles changes how the monkeys use the river.
They cannot simply enter the water casually.
They need speed.
They need awareness.
They need to reduce exposure.
And they need to keep moving.
The river is therefore not merely a swimming pool.
It is a dangerous environment where every second matters.
A Predator Beneath the Surface
Crocodiles are perfectly suited to ambush prey in water.
Their eyes and nostrils can remain near the surface while much of the body stays hidden.
That makes them difficult for a monkey looking down from a tree to detect.
The monkeys have to rely on speed and group behavior.
The Monkeys Have an Escape Option
There is one advantage to being able to swim well.
If a monkey falls into the water unexpectedly, it is not helpless.
It can paddle.
It can dive.
It can change direction.
And it can reach the riverbank.
This is an enormous advantage compared with a terrestrial mammal that cannot swim.
The River Is Also a Refuge
Interestingly, water can sometimes protect proboscis monkeys.
The New England Primate Conservancy notes that the monkeys may rest on branches overhanging water and can drop into the river if threatened by terrestrial predators.
So the same river can be both:
A dangerous place because of crocodiles.
And:
An escape route from predators on land.
That is the complexity of living in a riverine ecosystem.
A Perfect Example of Adaptation
The entire scene demonstrates adaptation at several levels.
The monkeys have:
- Webbed hands and feet.
- Strong swimming ability.
- The ability to dive.
- A tendency to leap into water.
- Group behavior.
- Maternal care.
- Strong climbing abilities.
Every one of these traits helps them survive in the unusual environment of Borneo’s river forests.
Why the Baby Is So Important
The infant is the most vulnerable member of the group.
It cannot make decisions about when to cross.
It cannot assess crocodile danger.
It cannot swim as effectively as an adult.
Its survival depends on its mother.
That makes the final crossing especially remarkable.
The mother does not leave the baby behind.
She carries it with her.
The Mother Is More Than a Swimmer
The mother’s role is crucial.
She has to choose the moment to jump.
She has to control her body in the air.
She has to enter the water safely.
She has to swim while carrying an infant.
And she has to reach the opposite bank.
One mistake could put both animals at risk.
The Group’s Survival Depends on Cooperation
Proboscis monkeys live in social groups.
That social structure provides benefits beyond companionship.
Moving together allows adults to monitor one another.
Young animals can follow experienced individuals.
Mothers can protect infants.
And the group can collectively respond to danger.
The river crossing shows how social behavior and physical adaptation work together.
What If a Crocodile Attacked?
The footage does not show a crocodile successfully attacking the troop.
That is important.
The title describes the river as crocodile-infested, but the visible outcome is that the monkeys successfully make the crossing.
We should not invent an attack that did not happen.
The danger comes from the environment and the known presence of crocodiles, not from a confirmed crocodile strike in this particular sequence.
The Crossing Ends in Success
One by one, the monkeys reach the opposite bank.
The mother and baby arrive safely.
The group is reunited.
The danger has passed.
The monkeys can now continue into the forest and search for the young leaves that motivated their journey.
It is a surprisingly successful ending to an extremely risky journey.
Why This BBC Earth Footage Is So Special
The video does not simply show monkeys swimming.
It shows an entire behavioral strategy.
The monkeys need food.
The food is across the river.
Crocodiles create danger.
The monkeys use trees as launch points.
They leap.
They swim.
They use their physical adaptations.
And the adults protect the youngest member of the group.
That is what makes the sequence so compelling.
Proboscis Monkeys Are Conservation Dependent
The species faces serious conservation challenges.
Its habitat has been reduced and fragmented by human activities, including the conversion of wetlands and forests.
Because proboscis monkeys are restricted to Borneo, protecting their remaining habitat is particularly important.
The species cannot simply relocate to another continent.
Its natural range is limited to one island.
A Species Found Only on Borneo
Proboscis monkeys are endemic to Borneo.
They occur in Indonesia, Malaysia and Brunei, particularly in suitable lowland and coastal habitats.
That makes Borneo essential to their future.
Protecting forests along rivers and mangrove systems can benefit not only proboscis monkeys but many other species that depend on the same ecosystems.
The Strange Nose Has a Purpose
The most famous feature of the proboscis monkey is its enormous nose.
Adult males have especially prominent noses.
Scientists believe the nose may influence vocal communication and female choice.
It may also amplify certain calls.
So the strange-looking nose is not simply an unusual feature.
It is part of the species’ social and reproductive biology.
A Monkey Built for a Very Specific World
Everything about the proboscis monkey seems connected to its environment.
Its long limbs help it move through trees.
Its hands and feet help it grip branches.
Its digestive system is adapted to a leaf-heavy diet.
Its webbing helps it swim.
Its social behavior helps groups move and survive together.
And its willingness to leap into water allows it to cross the rivers that divide its habitat.
The Great Leap of Faith
The BBC calls the sequence a “leap of faith.”
That description fits.
Each monkey reaches the edge.
The river waits below.
The animal cannot know with absolute certainty what is beneath the surface.
Yet it jumps.
It is a behavior that looks terrifying to humans but is part of the species’ normal survival strategy.
The Youngest Monkey Has the Biggest Challenge
For the baby, the leap is especially dramatic.
It has no choice but to trust its mother.
The infant clings.
The mother jumps.
They hit the water.
And the mother swims.
That tiny passenger represents the future of the group.
If the infant survives, it will eventually learn the same river-crossing skills itself.
A Lesson in Animal Survival
The sequence demonstrates a broader truth about wildlife.
Survival does not always mean avoiding danger.
Sometimes survival means learning how to move through dangerous environments.
The proboscis monkeys have not eliminated crocodiles from their rivers.
They have adapted to living alongside them.
They have developed behaviors that allow them to cross despite the risk.
Watch the Original BBC Earth Video
The original footage was published by BBC Earth on January 6, 2020, under the title “Proboscis Monkeys Leap Into Crocodile-Infested River.” BBC Earth identifies it as footage from Earth’s Tropical Islands, Episode 2, “Borneo.”
Watch the original video:
Proboscis Monkeys Leap Into Crocodile-Infested River — BBC Earth
More Wildlife Encounters From KHXYZ
If you enjoy wildlife encounters involving crocodiles, you can also read about four lions confronting a powerful crocodile, where a group of predators uses its numbers to overpower a heavily armored reptile.
Another remarkable crocodile encounter features two otters fighting a crocodile after biting its tail.
You can also read about a hidden crocodile attacking a leopard from below, showing how dangerous crocodiles can be when they use water as concealment.
For a very different animal crossing, see the baby warthog that used an incredible side step to escape lions.
And if you want another story about a mother protecting her young, read about the mother elephant carrying her stillborn calf.
