Declines of ≥90% occurred rapidly, averaging just 8.9 years along three roadside survey routes combined and 1.6 years at a 100-ha forested study site. Twelve species were likely extirpated as breeding residents on the main island, 8 others experienced declines of ≥90% throughout the island or at least in the north, and 2 were kept at reduced population levels during all or much of the study. Our results indicate that 22 species, including 17 of 18 native species, were severely affected by snakes. We analyzed two sets of survey data gathered in northern Guam between 19 and reviewed unpublished sources to provide a comprehensive account of the impact of brown tree snakes on the island's birds. Past studies have provided qualitative descriptions of the decline of native forest birds but have not considered all species or presented quantitative analyses. Predation by brown tree snakes (Boiga irregularis ) devastated the avifauna of Guam in the Mariana Islands during the last half of the twentieth century, causing the extirpation or serious reduction of most of the island's 25 resident bird species. Pacific Science 61:307–324.Impacts of the Brown Tree Snake: Patterns of Decline and Species Persistence in Guam's Avifauna Boiga irregularis, the brown tree snake (Reptilia: Colubridae). Biology and impacts of Pacific island invasive species. A snake in paradise: disturbance of plant reproduction following extirpation of bird flower-visitors on Guam. The study offers one of the clearest illustrations yet of how far-reaching the effects of an invasive species can be, and how difficult it is to get a genie back into its bottle. If these species are to survive, humans may have to step in to pollinate and replant the trees by hand. The few flowers that lizards or honeybees manage to fertilize simply aren’t enough to replace the trees, the researchers report.Īt least six more native bird- or bat-pollinated plants face the same problems, according to the article. Mature trees-established before birds vanished-are equally common on the two islands’ study plots, but Guam has fewer seedlings by a factor of about 50. Lizards showed the most promise, but even they tended to drink nectar more often than pick up pollen.Ī survey of tree saplings and seedlings showed the price the tree species are paying for the lost pollinators. Rats just gnawed at the flowers beetles favored older blooms that were past their prime. Most of the insects were too small to graze the flowers’ anthers. Worse, none of the visitors showed much aptitude for collecting pollen. On Guam, the same two trees hosted a parade of beetles, ants, butterflies, honeybees, crabs, rats, praying mantises, and lizards, but not a single bird. ![]() On Saipan, birds made 95 percent of the visits to the two tree species (most commonly, Bridled and Golden white-eyes and the Micronesian Myzomela). The two islands have similar growing seasons, plant species, and-until recently-bird populations. ![]() The authors watched two species of bird-pollinated trees-one a mangrove that grows in tidal flats, the other a thorny tree of forests and woodlots-on Guam and on nearby, snake-free Saipan. Brown tree snake electrocutions (the snakes climb power poles as well as trees) cause power outages every other day on average.Īlthough introduced animals still provide plenty for the snakes to eat, they fall short of native species when it comes to other ecological duties-a toll detailed in a recent article in Biological Conservation. With few native species left to eat, the snakes have moved on to eating rats and chickens. Today, hundreds of thousands of the venomous snakes cover the island, hunting everywhere from rocky shores to forest canopies.ĭuring the last five decades, the snake has eaten its way through 13 native bird species and two of the island’s bats. Twenty-two species of birds and three bats lived on Guam until 1949, when a pregnant brown tree snake slithered ashore from a cargo ship. Guam-a 200-square-mile island about 1,500 miles south of Tokyo-offers one of the most severe examples anywhere of extinction caused by an introduced predator. ![]() In the last five decades, a single introduced species has devastated the island’s fragile wildlife community-and now some native trees are feeling the repercussions as flowers open in vain and seeds never sprout. ![]() Snakes don’t eat plants, but on the Pacific island of Guam it’s starting to seem as if they do.
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