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The Mariana fruit-dove—unmistakable with puffs of vibrant colors across its chest and crest—today lives mostly in zoos and on four small Pacific islands. The pigeon disappeared from Guam, along with nine other native birds, eliminated by voracious brown tree snakes that likely arrived on ships after World War II. Scientists are starting to piece together the effects of their loss—among them the possibility of a thinning forest canopy increasingly riddled with holes, like Swiss cheese. They hypothesize that without birds to disperse seeds, fast-growing “pioneer” plants—like papaya and sumac trees—won’t fill the gaps.

To test their theory, they’re clearing small patches in Guam’s canopy and those of other bird-rich islands nearby, then tracking how quickly pioneer plants fill in the blank spots. Without a
full canopy, the forest may
be heating up, threatening wildlife and trees that thrive in cooler temperatures. “It’s very important to understand the implications of those [bird] declines,” says Rice University ecologist Amy Dunham. “The situation on Guam—which is tragic—provides us with
a unique opportunity to
see what happens when
all seed-dispersal services provided by animals are lost from an entire ecosystem.” And to help build a case for preventing such losses elsewhere.

This story originally ran in the July-August 2013 issue as "Missing Pigeons."