In the 1940s, a few snakes arrived in Guam hidden in military cargo; decades later, nine of the island’s 11 native forest bird species were gone

An island that had evolved without native snakes suddenly faced a predator its wildlife had never encountered before. In the late 1940s, brown treesnakes are believed to have reached Guam aboard military cargo ships or aircraft following World War II operations, as per the Archive for the U.S. Department of State, Diario AS, and U.S. Geological Survey.

The consequences unfolded over decades. The nocturnal, tree-dwelling snakes found an island where native birds had developed without snake predators and had few defenses against them. As the snakes spread, they preyed on birds and their eggs, eventually being linked to the disappearance of nine of Guam’s 11 native bird species.