A tiny, 200 square-mile island nestled low in the crescent of the Mariana Trench in the western Pacific Ocean, Guam is a United States territory first discovered by seafaring Indonesians around 2,000 BC. Populated mainly by Chamorros, the indigenous people of the Mariana Islands, Guam has long been a tropical paradise for birds, primarily because the island has no indigenous snake population.
But in the mid-1940s, that all changed. Shortly after World War II, the brown tree snake -- a infamously invasive species -- was accidentally introduced to Guam, probably as a stowaway on a cargo vessel. Since then, it has feasted royally, predator-free, gorging its way through the extinction of 10 of the island's 12 forest bird species. The two surviving species remain in tiny numbers in controlled areas. Guam's once cacophonous forests now lie silent. But besides the loss of birdsong, there are other effects caused by the absence of birds.
Biologist Haldre Rogers from the University of Washington is studying one possible outcome -- the loss of trees. Specifically, she's comparing the forest seed dispersal in bird-free Guam with that of nearby Saipan, whose forest has birds aplenty. In Guam, the trees drop their seeds directly on the ground below the tree. But in Saipan, birds feed on the trees' fruit, then fly to new locations, defecating seeds far from their original source.
Other research has shown that seeds that fall directly under their parent tree have a higher mortality rate than those carried elsewhere by birds. So for now, thanks to a hungry stowaway snake, the future of Guam's birdless -- and birdsongless -- forests look a bit grim.
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