[ Gentle instrumental music plays ] -Let's face it -- this isn't the world's most charismatic creature.

And neither is this.

And these tiny crawlers -- well, they don't look any cuter close up.

But ants, and opossums and even vultures have something in common with this beautiful fox.

They can all be found in our biggest cities, where they make a living by reusing and recycling what we throw away.

What we call garbage, they call dinner.

We don't always welcome them, but a new generation of scientists is discovering their secret lives... -They're really in every urban site that you can imagine.

-...the surprising ways they adapt to urban life... -Like, have you spent a few minutes just watching the cool things that they do?

-...and why we should care.

-There's really no other species that can fill that role.

-Together, they are the unsung heroes of nature's cleanup crew.

[ Upbeat instrumental music plays ] In the city that never sleeps, millions of tourists visit Times Square every year.

Most look up at the bright lights and skyscrapers.

Few notice the tiny hustlers at their feet.

If they did, they'd realize there are ants on Broadway, lots of them.

The entire city has 8 million people and an estimated 16 billion ants.

-Oh, the ant problem in New York is off the hook.

On a daily basis, I do pest control in one of the biggest cities in the country.

We basically deal with ants 24/7.

I had a customer that basically woke up one morning, made a cup of coffee, and basically swallowed ants.

So until this day, he doesn't drink coffee anymore.

♪ -These out-of-towners have a more ant-positive perspective.

They've come to New York to see the city from the ant's point of view.

-So when I first came to Manhattan, we didn't even know what species were here.

And what we found was 23 different species of ants on Broadway.

♪ -There's 2,000 ants for every human, and this just totally blew me away when I first came here.

And I was like, you know, I have to study this, I need to work in this city and understand what's supporting all these species.

♪ -Amy Savage and Clint Penick are among the world's top urban entomologists.

For nearly a decade, they've studied where the ants live... -Got some.

-...how they interact, and even how long they take to hunt and carry off a fly larvae.

-Ant on the card, in contact with larva, intonation grabbing.

It's picked it up.

Larva off the card.

-This summer, along with grad student Megan Rhone, their focus is a rarely-studied species called the pavement ant.

-One of the big things that they do is they pick up the food that people drop, and that's something we study.

♪ -Maybe they're dropping their hot dog, more likely their hot dog bun, they're dropping chips, cookies -- any kind of food that people drop, ants will clean that up for you.

They're really great in that way.

-Hey guys, check out these pavement ants on these chips.

-Oh, yeah, that's what it is.

-There's ants all over it.

-Every time we drop garbage on the sidewalk, ants are there to pick it up and clean up, even when we're slobs.

♪ -Foraging ants can lift over 10 times their weight.

They have to be quick because they've got competition from New York's massive rat population.

Rats can be dangerous to humans.

They transmit disease, but ants don't.

So maybe we should be rooting for the ants.

-I think this looks like a good spot.

-Yeah, I think so too.

-The team wants to know if ants or rats clean up more food waste.

-Here, you place that down.

-Okay.

-A crushed donut goes in a cage that allows ants to enter, but keeps out rats.

-Oh, that looks good.

-Yeah, that's perfect, yeah.

-The same amount of food goes outside the cage, where ants and rats can get it.

Who will eat more is anybody's guess.

-I might bet on the rats in this one 'cause I saw the rat bro back there.

So if it finds it, I think it'll be quick.

-All right, yeah.

-Let's see what happens.

-All right.

[ Gentle instrumental music plays ] ♪ ♪ -In this contest, the rats get off to a fast start.

They have a clear size advantage.

But does size matter?

Or will this be a numbers game?

♪ ♪ -You guys ready?

All right.

-All right, what's it look like?

-Well the one from rats has a little left.

-Yeah, I for sure thought rats would come out here and just scoop this up.

Obviously, I was wrong.

-Right now, what it looks like is that just as much food is gone from the tray where it was just ants, as from the tray with ants plus rats.

-I was amazed to find out that ants are actually eating as much if not more garbage than rats are in the city.

-That means less food for the rats, which also means fewer rats to transmit disease.

-So a lot of people find ants maybe useless or disgusting, and it's really unfortunate because they perform a number of these ecosystem services.

♪ -We realized that pavement ants in particular are basically nature's cleanup crew.

♪ -On Broadway alone, pavement ants consume the equivalent of a quarter million donuts per year.

If you piled them up, they would reach twice the height of the Empire State Building.

[ Traffic noise ] -Oh, my, you guys come here.

-Oh, wow, they're super active.

-Maybe it's from all the sugar in the cereal.

-Maybe!

[ Laughing ] -These female foraging ants are on a mission to take food home to their community.

-Do you think one of these ants could actually pick up a whole piece of a cereal?

-Not a whole one, but sometimes you'll see two or three ants carrying a big piece of food away.

♪ -In a way, they're commuters, because they don't live in Manhattan.

They live under it.

In an unseen world, beneath the human city, are many complex ant cities where foragers return with food for their mother, the queen.

Most of her eggs will become new female workers who do increasingly difficult tasks as they get older.

♪ -They'll start as nurses, and then they'll move on and start working on nest maintenance.

And then as they get older and older, they go out and become foragers, which is of course the most dangerous part of an ant's life.

♪ -And it's the oldest female ants who are on the frontlines.

-And E.O.

Wilson, the famous biologist, has a statement something like, "Humans send their young men to war, and ants send their grandmas."

[ Laughs ] ♪ -Without the grandmas' fight to get food, their colony could not survive or reproduce.

And when these ants do reproduce, they do it in spectacular fashion.

This is one time when lowly ants do get noticed, because they become airborne.

-And what happens is they all fly into the air and they mate in the air.

And in some species, the queen will mate with multiple males, most species just one, and then they all fall to the ground.

Males die, they're done.

-For some New Yorkers, like this man, the only good ant is a dead ant.

-I just received a phone call from a client out in Staten Island with an ant problem.

So we're heading out there now to eradicate that problem.

She really hates ants, and she's super freaked out by them.

-Okay Agatha, seems that we found the problem here.

You have an infestation with pavement ants.

-Oh, what freaks me out is they're gross looking and they have these creepy legs, and then they're so small that they can actually fit in, like, every little crevice.

So they serve no purpose aside from infestation and being a nuisance and causing problems.

-When I tell someone that I'm an ant biologist, there's always two questions I get asked.

The first question is, "Can you tell me what the ants are in my kitchen?"

And the second question is, "How do I kill them?"

-I understand not wanting ants walking on your food in your kitchen, but you know there are ways to deal with that particular behavior while still embracing the wonderful services that they provide us, especially when they're outside.

♪ -He may win this battle, but he'll never win the war, because on our entire planet, ants outnumber humans by a million to one.

-Ants are definitely abundant in cities, successful in cities, and then they're actually doing some good work for us as well, which is good to find out.

♪ -So I think that, in a way, we need to have more empathy with the species that share our cities and really embrace the fact that we do live in a diverse world, and that's a good thing.

If ants could speak to us, I feel like ants would say, "Just let us be.

Let us do our thing.

It'll be good for you."

-Ants aren't the only unsung heroes in nature's cleanup crew.

[ Upbeat instrumental music plays ] ♪ ♪ -They have that long rat-like tail.

They've got that nose that's like a star-nosed mole kind of thing, where it just comes out at you, and it's the first thing you see.

[ People screaming ] And they've got little red eyes, and then they're just sort of pointed.

-A baby opossum is stuck in the chicken food.

Oh my god.

-But when you see them, it's very upsetting.

♪ -People will call into our hotline, they're like, "It's just, like, a giant rat," but it's definitely not a rat.

Like, it's indescribable animal.

As soon as they hear, like, "Oh, and it's got this pointy face."

They're like, "Oh, you're talking about a Virginia opossum."

♪ -When left alone, the Virginia opossum prefers a quiet, solitary life.

If one is nearby, you might not know it, even if you are an urban wildlife expert like Suzanne MacDonald.

-My background is a little bit weird.

I am a psychologist who studies animal behavior, not human behavior.

About 10 years ago, I started doing studies on raccoons, urban raccoons that live with us in the city.

It was mostly motivated by laziness, because they were in my backyard, so why not study them?

-How smart he is, look at him go.

-But also because I was really really interested in these animals that everyone thought were super smart.

-Yeah.

[ Laughs ] -Look at him go.

♪ -While Suzanne studied raccoon behavior, her yard was visited by an opossum.

♪ -Nothing prepares you for an opossum.

Like, they have a face only a mother could love, really.

They are such a weird-looking animal.

I find opossums really interesting and also strangely charming because they are just super unusual.

♪ -Suzanne has designed an experiment to find out who will come to clean up food left out in her yard.

♪ -I have cameras set up all around the yard so they can get all the different angles of the chicken.

♪ Everybody who's in the vicinity will probably get the memo that there's a chicken available in the backyard, so let's watch to see what happens.

♪ ♪ -After night falls, the backyard receives some dinner guests.

♪ -It's sort of a battle out there of, you know, first the skunks, then the raccoons.

And I think it's pretty cool to think that as soon as we go to bed, everything else comes out.

[ Playful instrumental music plays ] -After everyone else goes home, an opossum arrives, late to the party.

[ Upbeat instrumental music plays ] ♪ ♪ -Because they really don't have the ability to fight anybody off, they pretty much get whatever's left over after the raccoons are done with it.

And opossums can digest bone, and they can digest pretty much anything.

They eat everything.

Whenever people say, "Oh, I don't like them," I always say, "Let me sell you on opossums."

And one of the things about opossums is that they also eat ticks.

-Look at that, that is so horribly disgusting.

♪ -We know that in the city, a pretty sizable proportion of ticks carry Lyme disease, and opossums will eat them with great delight.

♪ -Lyme disease causes severe pain and can be hard to treat.

An opossum can eat up to 4,000 ticks a week.

They provide this service in backyards throughout Toronto, even though they don't exactly belong here.

The Virginia opossum is native to the southern United States, but in recent years, climate change has extended its habitat north.

In Canada and the US, it's the only marsupial, a close relative of this more familiar animal.

Like all marsupials, opossums give birth to tiny undeveloped babies that make their way to their mother's pouch.

-She has 13 nipples.

If there are more babies than that, the rest of them die.

It's like a terrible game of musical chairs.

They grow for about three months, they come out and then they'll go up on their mom's back to travel around with her.

She can have two litters a year.

So if you have 26 babies a year, you're doing pretty well evolutionarily.

I mean, most of them may die, but you're pretty sure that some of them will live.

♪ -And sometimes, they could use some help from us to increase their odds of survival.

-Okay, I'll meet you out there.

Looks like there's a couple up there, and a couple down in here I'll use the ladder.

I'll go up and then I'll hand them down to you one at a time.

-Their injured mother was rescued, but died in surgery.

-These possums had a hard start to life.

They were discovered in their mother's pouch at a very very small age, they had just been born.

-Opossums are gentle little creatures and they really have no defense against predators, which is why they don't live very long.

But their big thing, their big go-to move when they are afraid, is to fall over as if they're dead.

♪ -To complete the illusion, they exude a smell like rotting meat.

After a while, they jump up like nothing happened.

It may look like a clever trick, but it's really an instinct, an evolutionary survival mechanism.

-So we don't know very much about opossum intelligence and I think that's because they kind of are slow-moving and they're weird looking and people think that they must therefore be dumb.

♪ -Suzanne wants to know if the conventional wisdom is true.

-So this is a dog toy, and it's supposed to challenge dogs who are left home alone, so it gives them something to think about.

And I thought, this is a great idea to test for the possums because it's colorful, it will attract them and it's got hidden compartments.

-There is some food in the pink compartments, but to get all the food, the opossum will need to figure out that you need to remove the white bones.

After Suzanne conducts the experiment, she reviews surveillance video.

-Oh my, she just comes in nose a-goin'.

[ Playful instrumental music plays ] ♪ Oh my god, look at her!

♪ She's doing exactly what a dog does.

♪ She took the bone out!

She removed the center portion, which is exactly what the dogs are supposed to do to solve the toy.

♪ So she figured out the flipping the lids instantly, and went for those bones and just chomped 'em and got 'em out of the way.

♪ I was completely gobsmacked by that.

That dog toy is a challenge for dogs, and the opossum figured it out.

She really showed me something I didn't think they had.

So, you know, looks can be deceiving.

♪ -Timing feels good, sun's beginning to set.

We should be at the release site right before sunset.

-Perfect, okay.

-The young opossums are now four months old and ready to live on their own.

-Virginia opossums are primarily active at nighttime, so we wanna put them out at their comfort time.

And being early in the evening, it gives them the entire night to move around, find food, find shelter, and just discover their new life in the wild.

-Yeah, we're good.

This urban park is very near where their mother was found.

-Collect an animal that needs rehab from a spot, that's it's home.

When you fix it, it should be returned home.

So just because you think, "Oh, there's a beautiful forest 5 blocks down the other place."

That animal's never been there before, and there's probably another animal that is already living there that's not gonna want them there, and they're gonna fight, possibly, and it could maybe even cost them their life if you take them to the wrong spot.

-Just around the corner.

-Yeah, just around the corner.

-For opossums specifically, we're looking for a lot of down debris that they can just kind of hide in and have natural spots to feel safe in right off the bat.

[ Gentle instrumental music plays ] ♪ ♪ Alright, I'm gonna open the kennel.

-People at parties always say, "Oh, these opossums, we have to get rid of them."

♪ They say opossums are ugly.

Yes, they are, they are ugly, but...

They say that they're dangerous because they're gonna bite people.

They don't bite people.

They say they dig up their yards.

They do not, they only use burrows and dens used by other animals, so they're not doing that at all.

They say they carry rabies, that they spread disease.

They do not do that.

In fact, they eat all the ticks and things that we don't want in our yards.

So pretty much every misconception, I can say, "No, that's not true."

And the more we learn about them, the more we're gonna love them, I think.

♪ -You worry about them a little bit.

They're so small, going into the big, wild city.

But end of the day, this is the best moment, yeah.

♪ ♪ That was really nice.

-That was perfect.

[ Upbeat dance music plays ] ♪ -Berlin is famous for its wild nightlife.

Less well known is its night wildlife.

Foxes are newcomers to the big city.

Like tourists on a pub crawl, they don't stay long in one place.

You see them, and then you don't.

Evolutionary ecologist Sophia Kimmig is on a mission to uncover the secret life of Berlin's most elusive party animals.

-What I personally find really interesting about foxes is that they are kind of torn between curiosity and fear always.

They colonize novel habitats, so they have to have a certain level of curiosity and boldness to make that step that other wildlife would never do.

And on the other hand, they are so shy and careful and they try to avoid us wherever possible sometimes.

And it's really fascinating how they're torn between those two extreme sides.

♪ I was always interested in mammals, but I have to admit that the fox somehow managed to make me fall in love with it.

-This warm feeling is not shared by everyone.

-Many people think that wildlife in the city is something like a pest.

Foxes have a lot of fans out there.

They just also have people that really dislike them.

People enjoy wildlife as long as it's far enough -- far enough away.

I think some of the negative perspectives are a historic relic because they used to be a carrier of severe diseases, so people actually had reason to be afraid of them.

But in our days, we do not have those diseases anymore.

♪ -It's quite obvious that foxes are here for the easy pickings.

They have become the newest members of nature's cleanup crew.

-They will not collect our plastics and recycle them, but when we throw food, they eat it.

So they kind of clean up behind messy people.

And the other thing is that we have rodents and we have rats in the city, and foxes hunt them, and they eliminate pest species.

We have some areas in the city where we have too many rabbits.

And the city is almost desperate about getting rid of them.

♪ -The prolific rabbits devour gardens, and their burrows undermine roads.

♪ -Foxes hunt them, and you don't have to make them do it, they just do it.

So in this case, they help the city of Berlin to reduce the rabbit population.

♪ -In a single year, Berlin foxes feast on more than a million rodents and rabbits and eat enough cast-off food to divert at least 30 truckloads of waste from landfill.

♪ Foxes enjoy the street food.

But can these woodland creatures really thrive amid the concrete and the noise?

♪ -And I'm interested in, how do they cope with that?

Where do they go?

Where do they find spots where they can still hide?

Where do they breed?

How do they change by living in the city?

-To find out, Sophia plans to monitor their movements.

But first, she'll need to catch one.

[ Playful instrumental music plays ] ♪ In the wild, the fox's acute sense of smell would warn her about objects that have been touched by dangerous humans.

But in the city, everything smells like humans, so it's hard for her to recognize a trap.

Under Sophia's direction, the fox will be sedated and fitted with a GPS collar that can record where it goes.

-Some people are concerned, like, "Those poor foxes get those collars and have to walk around with them."

But for me, the more relevant question is, are those foxes okay in the city?

♪ [ Conversing in German ] ♪ -Sophia's radio direction finder will help her find the fox and retrieve location data.

[ Gentle instrumental music plays ] ♪ ♪ There's a good chance that while she looks for the fox, the fox is watching her.

♪ -Actually I will not see it, probably, because they are hidden somewhere.

They're really good in hiding right in front of us.

If you walk around here, you can realize that there is a very distinct foxy smell in the air, so I know that there are some.

But what I'm really interested in now is if my fox is here.

Yeah, when we hear that sound, then we are quite close.

And when you're lucky, then you get close enough to get to the data.

[ Gentle instrumental music plays ] ♪ ♪ We just uploaded this from last week.

So we can see now for every four minutes where the fox has been in the last week.

-This is just one of 17 foxes that Sophia is spying on.

-So every color that you see here is a different individual.

Like the pink one is a female fox down here, which is a coincidence.

And the blue one up here was the one living in the presidential garden.

When the fox go somewhere more often, then the color's more bright.

Here, you can perfectly see that there are spots that they prefer to use or where they spend lots of time.

♪ -Now, Sophia can visit these secret places to discover how foxes are adapting to the city.

It turns out, they have found places to hide and secluded homes for their young.

But the data also show another side.

-This is a really big street that is crowded with traffic, and it's crossing it continuously.

So we can see why the lifespan of an urban fox is so short.

It's really hard to have a definite answer to the question whether they're doing well here or not.

♪ -Sophia can't make the city safe for foxes, but she hopes to convince more Berliners to welcome them.

-There actually are services that wildlife provides, like collecting garbage, killing rats in the city.

On the other side, wildlife has an intrinsic value beyond any kind of service that it can have for us.

I would really love to one day see the city through the eyes of a fox.

♪ ♪ -So far, we've met scavengers that clean up trash that we can clean up for ourselves.

But we have bigger problems.

-A huge new leak, one of the biggest oil spills ever.

♪ -Can nature's cleanup crew handle the tough stuff?

In a biochemistry lab lives a strange species, weirder than opossums, smaller than ants, and from a family with a reputation for making us sick.

♪ These bean-shaped things are bacteria named Alcanivorax.

♪ During a recent oil spill disaster, they were found at great depths, eating the oil.

That was strange, because most bacteria can't do that.

-Alcanivorax is an incredible bacterial species which loves to feast on the petroleum oil hydrocarbons, as it gives them their source of energy.

And no other bacteria can do this wonderful job.

♪ -Microbiologist Satinder Kaur Brar wants to know if Alcanivorax will eat oil underground -- the kind of toxic goo spilled by millions of rotting tanks and burst pipelines throughout the world.

♪ -There are many sites which have been abandoned and which have petroleum oil contamination in them.

Sometimes, the oil-contaminated soil is dug up and removed, but then it just ends up somewhere else.

At times, chemicals are used, but that too leaves residues that may also turn out to be toxic.

I've been working to find a biological solution that might be better.

♪ -After acquiring waste oil from a garage and Alcanivorax from a microbe repository, she puts them together.

-I think this is the final... -It's the final.

-...addition of your oil into the medium.

[ Upbeat instrumental music plays ] ♪ ♪ -A time-lapse reveals that something is going on, but the real action is microscopic.

Each tiny bacterium releases even tinier enzymes.

What makes the Alcanivorax enzyme unique is the size of the dimple on its side.

It's large enough to trap a heavy oil molecule and rip it apart.

-In simple terms, they are the scissors which the bacteria needs to cut into the petroleum oil hydrocarbon.

♪ -The resulting atoms of hydrogen and carbon are scooped up by the Alcanivorax bacteria.

♪ -Inside the bacteria, they are transformed into energy so the bacteria can grow and reproduce.

What is expelled is non-toxic carbon dioxide and water.

♪ -But will this work in the real world?

Satinder and her team intend to find out.

-Hi, Thomas.

-So we're standing here today, on the site of a former gas station.

The gas station was used in the '50s, and it was used afterwards for petroleum storage.

And what happened, over the years, oil leaked from those reservoirs into the ground.

First, what we do is we dilute the enzyme concentrate in the process tank.

And then we use a pump to pump it right into the well and into the contaminated soil.

-It gave fantastic results in the laboratory, and now the only crux was whether this would translate in the field.

-After a couple of weeks, what we'll do is we'll come back on this site, we'll drill more holes and we'll see what was the effect of the enzyme on the level of contamination.

-Over those two weeks, the enzymes seeped through the soil, making contact with the oil deposits.

♪ [ Speaking in French dialect ] ♪ -Tests reveal that almost all the oil is gone.

♪ -So the enzymes, after a certain time, will break down into non-toxic components which become part of nature.

♪ -You do not need excavators, you do not need trucks, you don't rely on bringing the contaminated soil to another disposal site -- the soil is treated in place.

-The site has been contaminated for the last few decades, and the enzymes produced by the incredible Alcanivorax can do the cleanup job just in one to three weeks.

♪ -This successful trial was small scale, but soon, Satinder hopes to try Alcanivorax on a much larger spill.

If it works, unique bacteria found in the sea could become an important tool to combat oil contamination around the world.

-80% of the bacterial species, they work for us.

It's only the 20% that are pathogens.

So we shouldn't be scared of bacteria, we have to embrace them.

They are our friends.

They are not our foes.

♪ -Few of us can recognize beneficial bacteria, but it's common knowledge that a vulture is bad news.

-Let's not be melodramatic, Harry.

You're not going to die.

-No, I'm dying now, ask those things.

-The vulture is often portrayed as a portent of doom.

♪ But conservation biologist Evan Buechley sees them differently.

-They're large, colorful birds.

They're exquisite fliers.

They're really elegant when they're flying.

Vultures are the highest flying birds in the world.

They can slowly glide for hundreds of kilometers.

♪ They're some of the most intelligent birds in the world.

They have some of the keenest vision, strong senses of smell.

So you can have an animal that dies -- within five minutes, vultures are circling over and dropping down and starting to feed.

Vultures actually consume more animals than all the lions, the jackals, the hyenas, the leopards combined.

♪ -In Ethiopia, they clean up carrion in the wild, but also live in the bustling city of Addis Ababa.

♪ So what are vultures doing here?

♪ -So we're gonna go to a abattoir, which is a traditional slaughterhouse here in Ethiopia, where animals are slaughtered for human consumption.

People rely on the vultures to come in and feed on the waste and clean it up.

It's a very ancient system that's been in practice for hundreds if not thousands of years.

♪ -Evan and his colleague, Eleazar Dukkah, observe humans and vultures at work.

-We got about a dozen hooded vultures, and then there's a few white-backs.

So that's been a nice bout of feeding this morning.

♪ They're pretty fierce when they're fighting for the food like that.

[ Gentle instrumental music plays ] ♪ By offering and placing out the food for the vultures and then having large populations of vultures come and quickly and efficiently clean up the waste, it's a win-win solution for both.

♪ In other parts of the world, where we rely on big garbage dumps or incineration, it's a very kind of inefficient way to process that food.

And so I think there's ways in which we could really learn from this system.

♪ -The vulture is uniquely adapted to clean up carrion.

Its acidic digestive system neutralizes deadly pathogens including botulism, cholera, and anthrax.

-And then when they defecate, the viruses and bacteria are largely absent.

We think of vultures as being maybe dirty birds -- they're eating these dead animals, they're gross, they're icky -- but really, they are critically important.

Vultures, by consuming carcasses, are really actively helping to eliminate disease from the environment.

♪ -While vultures thrive in Ethiopia, elsewhere in Africa, they are endangered by elephant poaching.

Because the vultures' quick arrival alerts authorities to the crime, poachers want to eliminate vultures.

They douse carcasses with a poison that overpowers the vultures' iron constitution.

-There's been several cases now of several hundreds of vultures dying from a single elephant poisoned carcass.

So it only takes a handful of those events to drive vulture population declines across many countries.

♪ Luckily, in Ethiopia, these main threats seem to be largely absent.

-This may be because of Ethiopia's long history of human-vulture collaboration.

But even here, they are vulnerable, because at some abattoirs, feral dogs get in.

Unlike vultures, dogs' stomachs did not evolve to kill pathogens.

So when they eat rotting meat, they contract diseases and pass them to humans through their feces.

[ Dogs snarling ] -The dominance of the dogs at this abattoir is something that's happening all over the country and is really troubling for people, for human health.

Over the past three decades, the seven vulture species across Africa have declined by 70% to 97%.

♪ -In Africa and around the world, hunting, poisoning, and habitat loss have put many vulture species at critical risk.

-It is something that everybody should really worry about.

Because as vultures decline, we have evidence and growing evidence from around the world that human disease will increase.

You could lose an insectivorous bird species or a pollinating bird species, and that would be a tragedy, but the ecosystem largely would be able to continue and fill that role with other species.

But if you lose even one vulture species, there's nothing that's gonna be able to really replace that function of consuming that carcass, from removing the disease from the environment.

So, vulture conservation and vultures in ecosystems are extremely important.

♪ -Evan and Eleazar want to know where vultures go when they leave the relatively safe borders of Ethiopia.

-I think this is a good spot.

-To find out, they hope to trap a vulture and attach a satellite transmitter.

-Birds are really smart and they're really, you know, the one time in their lives when they're at risk at all is when they're on the ground feeding.

And so we need to be really thoughtful about making sure that everything seems as normal as possible.

Trapping is always nerve-racking.

So, like, I'm always a little on edge until we actually, like, get it done.

-The flock takes to the air because a bird has been caught in a trap.

♪ It turns out, it's a raven.

-There's a bunch of different species that come in and scavenge.

It's a fantail raven.

A lot of times, the first thing you catch is not what you planned on catching.

Not a vulture -- it's a beautiful bird.

So it's not ideal, but it's part of the process.

♪ -They try again at a series of different locations.

♪ -All right, so after five days of waiting and moving traps and trying many times, we finally managed to catch a white-backed vulture.

♪ We'll attach a satellite transmitters on them using a harness that we build.

These satellite transmitters weigh less than 3% of the weight of the bird, and studies show that they don't harm the bird.

But they allow us to collect detailed points of precisely where the birds are going every hour throughout the day and night of their lives.

[ Upbeat instrumental music plays ] ♪ ♪ So we have tracks here of many different vultures that we've tagged over the last couple of years.

For the first time, we get to see exactly where these birds are moving.

That lets us identify where they're feeding, where they're roosting, where they're nesting, and eventually also where they're dying.

So we've had birds that we've tagged here travel through more than 20 different countries and cover many, many thousands of kilometers in their migrations and their journeys.

-Their migrations pass through places where they're not appreciated or protected.

♪ -So conservation of vultures really cannot be within one country or within one continent.

It really needs to be kind of broad scale across continents.

-For eons, vultures have migrated from Africa across the Mediterranean into southern Europe.

♪ But during the past century, their numbers fell.

The Arda River Valley was once their summer home.

♪ Conservationists are determined to bring them back.

♪ -This is the bearded vulture, and nowadays, they doesn't exist in our nature.

And this is our main goal in the rescue center, to reintroduce the species back to Bulgaria and to the Balkans.

-The Green Balkans Rescue Center cares for and breeds several endangered species.

-At eight weeks old, they are prepared for release into the wild.

-You are beautiful.

Don't die in the sea.

Don't perch on dangerous power lines.

Do not eat poison.

[ Indistinct conversations ] ♪ -It's important to take them to the right spot.

♪ To reach it, these volunteers climb for hours with fledglings on their backs.

[ Gentle instrumental music plays ] ♪ Their destination is the valley where vultures once ruled the sky.

-Precious cargo is here.

[ Laughter ] -The young ones are lowered, carefully, off the cliff.

♪ ♪ ♪ In a natural cave, a metal screen protects them from predators.

For a few weeks, they will live here alone, fed each day through a tube.

From this point on, the birds will have no human contact.

[ Upbeat instrumental music plays ] ♪ -It is my hope that through understanding the important role that vultures play in ecosystems, we'll be able to help to change the images and perceptions of vultures in society so that people appreciate more the role that they have in ecosystems and the benefits that they provide to humans free of charge.

♪ If vultures could talk, perhaps they would say, "Give me some respect, man."

♪ -For all our unsung heroes, respect would be a good start.

Because while some may seem strange or weird, or even disgusting, they make our cities cleaner.

So maybe we should relax a little, and make some space for them.

We help ourselves when we let them live in peace.

♪ ♪ ♪ ♪ ♪