The next phase of the Rewilding Argentina campaign is to introduce some females to this part of the world, and, with a little bit of luck, there'll be a vibrant, wild jaguar population here.

And I'm very excited to be witnessing this little piece of rewilding history.

♪ ♪ And I was excited to meet up with an old friend.

Ah, Sebastián, my friend.

-Hi.

Hi, Miles.

How are you?

O'BRIEN: Sebastián di Martino.

Bring it in, bring it in.

-Ah, nice to see you.

O'BRIEN: It's been five years, how are you?

Yeah, five years, five years.

-Five years.

He was the conservation director.

You will not believe what you will see here now, yeah.

- Yeah.

Sebastián took me to the enclosure where jaguars destined for the wild here in El Impenetrable are acclimated before release.

So now we are trying to replace the breeding in captivity program by the translocation of wild animals.

That is much faster, is more efficient.

O'BRIEN: Acaí was already here, but she was out of sight.

As was another female, Miní, who was hours away from release.

DI MARTINO: The last record of a female was, uh, 1990.

So, 35 years ago.

So, last year, we started to release females, and we released two, and tomorrow, we are going to release the third one.

O'BRIEN: Rewilding is not complete until the apex predators return.

Their presence triggers a trophic cascade, a chain reaction that ripples through the food web, helping restore balance across the landscape.

Top predators influence how their prey behave.

KRIS TOMPKINS: Everybody's on the alert.

They need to hide again, instead of lounging in the middle of roads and so on.

So, behaviorally, everybody comes back into line when the top predators are back.

♪ ♪ O'BRIEN: The apex animals of the waterways here are the giant river otters.

(squawking) The otter, as, as you can see, they are very noisy, they are diurnal, they are, uh, live in big groups, and they are very curious.

So, yeah, they are spectacular animals, very charismatic.

O'BRIEN: And they became at least locally extinct... DI MARTINO: Yeah.

...because of why, what happened?

So, most of the historic records of giant otter is people shooting the groups because it was fun.

And when you shoot one of the members of the group, the others tend to stay.

They are trying to help the one that is injure or dead.

So it's kind of easy to shoot them, them all, yeah.

People... That, that is some horribly sick fun.

DI MARTINO: Yeah, it's, but that's the culture of that time.

(otter squawking) So... O'BRIEN: I think they want out, don't they?

MAN: Yeah, they want out, yeah.

(all laughing) (otters squawking and squeaking) O'BRIEN: For Sebastián, the bold idea of restoring entire ecosystems isn't just a conservation mission.

It's a boyhood dream brought to life.

DI MARTINO: As a kid, I was always dreaming, like, it would be great to have, like, a time machine to go back in time to create, like, a big national park and preserve the environment and all the species.

O'BRIEN: Sebastián was ready to write the next chapter in his time machine story.

Not far away, Miní was ready to step out of the confines of her enclosure to spend the rest of her days in the wild.

It's like seeing your kid off to college or something or... Something like that.

(both laugh) DI MARTINO: She will be monitored with a collar that has a GPS that collects points every three hours, and every day, we get the position points, so we know where she is.

♪ ♪ O'BRIEN: And right now, her position point is nowhere near us.

Yeah, she's far away.

O'BRIEN: And that seemed to me like a wise time to open the door.

♪ ♪ So, we will open this door right now to allow Miní to get out and start her free life in El Impenetrable.

O'BRIEN: All right.

DI MARTINO: Yeah.

O'BRIEN: An exciting moment.

DI MARTINO: Now we only have to wait.

She will go out maybe in a couple of hours, maybe in a couple of days, but... O'BRIEN: Excellent.

Congratulations.

-No, con.... Yeah.

-Yeah.

O'BRIEN: Let's let nature take its course.

♪ ♪ Several hours later, long after we'd left, Miní edged her nose through the open door, didn't smell us, then padded off into the wild.

♪ ♪