“Cathartes aura. The purifier. Not the devourer, not the harbinger, but the one who cleanses. They arrive in the wake of death and leave the world measurably better than they found it. When vulture populations collapsed in India in the 1990s, human mortality rose sharply in the affected districts as waterborne disease spread through decaying carcasses. Half a million additional deaths, by some estimates, before anyone understood the connection. We rarely appreciate what they do until they are gone.”