For 70 years, the small brown-and-gray songbirds stashed in a drawer at the Smithsonian were a mystery that no one thought to question. Their labels read White-crowned Tapaculos, a species native to mountain forests across equatorial South America. But as scientists recently discovered, the birds are actually an entirely unique species. This species, which is named the Perijá Tapaculo, after the mountain range in which it lives, is the newest member of a group of tropical, New World songbirds that forage for insects near the ground. It’s a perilous practice (“tapaculo” essentially means “cover your ass” in Spanish) that leaves them vulnerable to predation. A few species sport bright colors and patterns, but the majority are somber in shade—hence the ambiguity. Of the 50 known species of tapaculos, 10 have been discovered within the last 20 years, thanks to DNA analysis and vocalizations. “The recognition of the new tapaculo in the Perijás is welcome and exciting...