JOHN YANG: And finally tonight, the populations of some of Africa's most iconic animals have been bouncing back thanks to decades of conservation efforts.

But activists are warning that climate change and human activity are shrinking their habitats.

Now a nature preserve in central Kenya is pushing to set aside more land to connect with other preserves to allow wild animals to roam freely.

JOHN YANG (voice-over): At the Lewa Wildlife Conservancy, it takes planes, Jeeps, binoculars and a lot of patience to count the animals by hand.

Dominic Marenga is Lewa's head of conservation.

Each year, his team conducts a census of the 60,000 acre sanctuary.

DOMINIC MARINGA, Lewa Wildlife Conservancy: All this is an effort to ensure that we undertake responsibility of accounting for every species that is found on Lewa, especially the most critically endangered ones, the threatened ones.

And we make sure it is a full census.

JOHN YANG (voice-over): A full census to track the growing population, including elephants.

Their pregnancies last nearly two years, the longest of any living mammal.

In 2014, there were 350.

By 2024, their population had grown to 450.

There's been a similar increase in rhinos.

In fact, the sanctuary is home to 14 percent of all black rhinos in Kenya.

It reflects a nationwide wildlife comeback.

In the 1980s, Kenya's elephant population was around 16,000.

By last year, their numbers had climbed to 37,000.

But habitats are shrinking.

Among the causes, climate change and urbanization, both spurred by a human population boom.

Now Kenyan wildlife officials are encouraging conservancies to create more of what they call wildlife corridors, protected strips of land connecting large habitats like Lewa with other rangelands that would otherwise be separated by human activity.

They allow animals to move freely, reduce chances of human interaction, support wildlife population growth and boost tourism, which generates billions of dollars a year.

Lewa plans to add more corridors to the ones they've already created.

DOMINIC MARINGA: If you are in an enclosed ecosystem, the population will have to filter out one way or the other.

And who are they going to meet outside?

The farms, you know, retaliatory attacks.

So you think ahead.

Open new corridors.

Connect your conservancy with others.

JOHN YANG (voice-over): The Lewa Conservancy hopes that would help animals that have existed for millions billions of years thrive alongside humans for millennia to come.