When wildlife photographer Joel Sartore photographed northern white rhino Nabire, she was one of only five of her species left on Earth.

Since then, she’s died, and there are only three northern white rhinos remaining.

Nabire, a northern white rhinoceros, was one of the last five of her species when Joel Sartore photographed her. Now there are only three left on Earth. Credit: © 2016 Joel Sartore Photography Inc.

“People ask me all the time if I get depressed,” Sartore said of photographing some of the rarest species on Earth. “I don’t get depressed, I get mad. And I get inspired to want to use their stories and really get the world to try to pay attention.”

Sartore has spent the past 11 years photographing more than 6,500 species around the globe for his "Photo Ark."

This is an endangered Von der Decken’s sifaka, a type of lemur, which Sartore photographed in Madagascar. Credit: © 2016 Joel Sartore Photography Inc.

The National Geographic project aims to create a collection of digital portraits of the roughly 12,000 animals in human care around the world, in some cases to document species before they go extinct.

All of the photos are shot against a black or white background with studio lighting. The setting strips animals down to their essence, removing the distractions of muddy water or view-obscuring tree branches.

“We’re able to look these animals directly in the eye and see that there’s great intelligence there and that they’re worth it — they have a basic right to exist,” Sartore said.

“Beyond that, [the studio setting] is a great equalizer. A mouse is every bit as impressive and large as an elephant.”

Sartore focuses on animals in zoos and wildlife refuges to make these studio-style portraits possible.

His goal: to show the world what biodiversity looks like, and get people to care about saving species while there’s still time. Roughly half of the world’s species could go extinct by 2100, Sartore said.

“If we doom half of everything else to extinction and expect humans to be just fine, it’s not going to work,” Sartore said.

The inspiration for the "Photo Ark" project came to Sartore back in 2005, when his wife, Kathy, was diagnosed with breast cancer.

Wildlife photographer Joel Sartore is pictured.

His career as a National Geographic photographer came to a halt as he spent a year at home with his family, while his wife successfully underwent treatment.

“During that year at home, I had the chance to stop and think about my life,” Sartore said.

The magazine stories he shot for National Geographic came and went, and he wondered what he could do that would really make a difference in the world of conservation.

“What can I do right this moment to try to get people to pay attention to the extinction crisis that’s coming?” Sartore asked himself. “As a photojournalist, this is my best solution for that. ... I hope it’s just not a record of what we squandered.”

Sartore’s photographic quest is the focus of a three-part series called “RARE — Creatures of the Photo Ark” airing on PBS starting tonight and streaming on PBS.org.

This is Raja, a white-crowned hornbill with a ferocious beak that Joel Sartore photographed for the "Photo Ark." Credit: © 2016 Joel Sartore Photography Inc.

Listen above to host Marco Werman’s interview with Joel Sartore to hear him talk about his most dangerous moments in the field, from being chased by a mama grizzly to being exposed to the deadly Marburg virus.