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The olona shrub is one of many forest plant species native to Oahu (a Hawaiian island) that are at risk of extinction. The survival of most of these species in the wild largely depends on birds eating their fruits and then dropping the seeds in different locations. Although Oahu's native fruit-eating birds have all gone extinct, the common waxbill and other fruit-eating bird species have been brought to the island and are now common there. Studies confirm that these non-native birds are spreading plant seeds on Oahu, suggesting that the birds ______