In the late 1960s, while the world preoccupied itself with rock-'n'-roll and flower power and moon landings, a small bird far out in the Indian Ocean came within a hair's breadth of vanishing forever.

This early success gave the team the confidence to try reintroducing the species to other islands where it formerly lived. In 1994, they established a population on Cousin, a 70-acre island that had ...