Visitors to Guam’s forests find them quiet–eerily so: No chirping of birds can be heard overhead. But slithering in the shadows on the ground are snakes, each some six feet long. Brown tree snakes made their debut on Guam, the southernmost island in the Mariana Archipelago, when islanders were rebuilding after World War II. Most likely, they were stowaways in lumber shipments heading north through the Pacific Ocean from New Guinea. They quickly began feasting on the birds and small lizards they discovered in Guam’s dense forests, and–free to slither through the mountainous terrain without predators of their own–they completed an invasion of the island at a pace of one mile per year. By the late 1940s, the forests had largely fallen silent, and now, all of Guam’s native bird species are history.