This is 99% invisible. I'm Roman Mars.

This past fall, 200 people gathered at the Explorers Club in New York City.

The building was once a clubhouse to famed naturalists and explorers.

Now it's an archive of ephemera and rarities from pioneering expeditions,

from treks to the world's tallest mountains, the North Pole, and the Moon.

Woolly mammoth tusks frame a fireplace, a menacing polar bear towers near the landing with claws at the ready.

And a cheetah rumored to have been shot by Teddy Roosevelt sits on a plinth just upstairs.

The gathering was an honor of a new expedition. One in search, not of a single animal, but of thousands.

Best reporter, Caitlin Swaljay.

The club was hosting a biological census. An ecological survey so difficult,

so complicated, so taxing, that it had never been attempted before, and may never be attempted again.

It is a really big project. Like, I don't think we've ever been involved in a project of this

scope in our lives. It's like moving a little, a small little armory around.

This is Jamie Allen. The census was his idea. And when he started, it was a small operation.

But now Jamie is merely the tip of a vast pyramid of census-related personnel,

including a logistics chief, a chief cartographer, a veterinarian, an epidemiologist,

a specialist from the Fish and Wildlife Service, and of course, a web team.

And that's just the core staff. Below them are the foot soldiers,

the volunteers who must go out into the field and do the actual counting.

300 plus volunteers counting 700 hectares, 100 meter by 100 meter, and 3,000 plus sheets of paper

that we have to... it's... yeah. A vast filing system, multiple offices, and a team of hundreds,

all for the sake of answering one question.

...