AP Photo

Delmi Morales Nosa never imagined she'd need her family's bow and arrow for anything other than hunting. But when construction started last year on a highway set to bisect her homeland, Bolivia's second-largest national park (known here as Tipnis), she reconsidered. "The road will ruin our way of life, and we will defend ourselves by any means necessary," said the indigenous Yuracaré mother of two, as she shoved wood into her outdoor adobe oven. Having survived centuries of incursion by the Spanish, rubber traders, and loggers, the park's residents say the road -- which environmental impact studies predict could contaminate the Isiboro and Sécure rivers and push 11 endangered species toward extinction -- represents the gravest threat yet. Surveying the remote...