Why are some creatures, like robins, so common, while others, like the maned wolf, so rare? Surprisingly, human activity isn't to blame in most cases. Rarity, it turns out, is very common in nature, and of the estimated 15 million species on Earth, most are very few in number. One wildlife biologist is tracking the planet's rarest animals in hopes of understanding why they’re scarce and what it means for other species. We explore his research, and how technology is helping catalog the world's biodiversity.