vulture

A vulture is a bald-headed bird that feeds on dead animals. It circles, waits, and comes down when nothing is moving.

The bare head is an adaptation, since feathers would clog when feeding inside a carcass. They are genuinely essential, because they clear disease from a landscape faster than anything else, and their collapse in South Asia caused a public health crisis. The figurative use is entirely negative, so calling somebody a vulture means they profit from other people's disasters, and vulture funds buy distressed debt.