Yellowstone’s reintroduction of wolves in 1995 is one of the best-known instances of a trophic cascade – a single change in a food chain that transforms an entire ecosystem. The return of the wolves rejuvenated wildlife in the park from top to bottom, even changing the area’s physical geography as native animals and plants reasserted themselves. Narrated by George Monbiot, How Wolves Change Rivers chronicles how Yellowstone’s extraordinary success in rewilding stems from a decrease in invasive and overpopulated species such as coyote and deer thanks to just 66 wolves returning after a 70-year absence from the park.