Wolves returned to Yellowstone

And rerouted the rivers.

When 14 wolves were reintroduced in 1995, they thinned the elk herds that had overgrazed the valleys. Willow and aspen grew back. Beavers returned. Songbirds returned. The regenerated forests stabilised the riverbanks — and the rivers themselves changed course. Ecologists call it a "trophic cascade." Poets might call it something else.

Editor's Note