Samoa guide. 34. Pest invaders are here

Another example is of an invasion that is still under way -- by introduced birds. The first bird introduced to American Samoa was, of course, the chicken (moa). Although these occasionally nest in the forests, they are not truly established as wild birds here, and are no threat to our native birdlife. However, we do have three introduced bird species on Tutuila. One of these is the manu palagi, or Red-vented Bulbul, the black bird with the crest that is common in nearly every village. This species became established here in the 1950's. The other two species both arrived in the 1980's and there seems to be no name for them in Samoan. These are the Common Myna and the Jungle Myna. They look almost the same -- both are blackish brown, with big white patches in the wings and tail when they fly. They are now abundant from Pago Pago to Leone and are spreading to the eastern and western ends of the island. None of these three introduced birds has made it to Manu'a, which is still home to only our native Samoan birds.

The lesson to learn from these examples is that we must be very, very careful when thinking about introducing a new plant or animal to Samoa. Even species that seem beneficial, like the predatory snail, can have bad and unforeseen effects. And once a new species is established, it is almost impossible to get rid of.
Wisely, the Territory has established strict laws against bringing in exotic animals and any plant that may become a noxious weed. Flowering plants, like Honolulu rose (Clerodendrum chinese), may look pretty in a garden but turn into major pests when they run wild.

Unfortunately, the story does not end there. In the hopes to control the giant snails, a predatory snail (Euglandina rosea) native to Florida was deliberately introduced here in 1980. The idea was that this new snail -- the one with the long pinkish shell -- would kill off all the giant snails. Instead, it has driven the native land snails of the Pacific islands to the edge of extinction. Most of the native snails of Tahiti are now extinct, and the Samoan snails, which used to be collected by the thousands to make ula, are almost gone. Meanwhile, the giant snail continues tothrive despite the new predator.

The first Samoans were also such lucky adventurers, making the perilous voyage here in their journeying canoes. But their arrival marked the beginning of a new way for plants and animals to reach our islands -- being carried here, either by accident or on purpose, by people. Ever since then, the environment of American Samoa has changed tremendously.

Some of these changes may have benefited some wildlife species. For example, the introduction several important food plants such as breadfruit and bananas provide a year-round source of food for some birds and fruit bats, rather than seasonally like some native plants that are eaten by wildlife. Other changes brought by the Polynesians were harmful to the environment -- for example, the introduction of rats (isumu). And since the arrival of Europeans and Americans, the rate of introduction of new plants and animals to American Samoa has increased tremendously. The results have often been disastrous.

Some plants brought by the Polynesians “escaped” to spread widely through the natural forest such as ifi and nonu trees. More recently, about 250 alien plant species (many of them weeds) have also become established in American Samoa and some of these threaten our native forest. One that is familiar to everyone is the “mile-a-minute” vine, or fuesaina (Mikania micrantha). This was introduced by accident, sometime before 1924. It is now a major pest in plantations and forests, and has spread tremendously following tropical cyclones in the early 1990s. The vine needs sunlight for its very fast growth, and so doesn't do well inside the shade of the mature forest. The cyclones, however, opened up the forests to sunlight by knocking down many trees and breaking off the tops of thousands more. Vines like these can form layers several feet thick that can choke the seedlings of native trees and slow the recovery of our forests from the damage of the cyclones.

Another well-known pest to agriculture is the giant African snail (sisi aferika, Achatina fulica). This was reportedly introduced to the Pacific when the governor of Tahiti imported them to satisfy the hunger of his mistress for escargot, or edible snails. Bad, bad idea -- not only were the snails not edible, but they quickly spread throughout Polynesia, and became a major pest of taro and other crops.

What's wrong with having new kinds of birds to live in our villages and gardens? In some parts of the world, including Hawaii, both bulbuls and mynas are serious pests on fruit crops such as guava. Second, they may spread the seeds of pest plants, like mile-a-minute vine and “Koster's curse” weed (Clidemia hirta), that native birds do not eat as readily. Third, they may drive out native birds, like the iao or Wattled Honeyeater. Although we don't know for sure that this is happening, there seem to be more iao around villages in Manu'a than on Tutuila where the introduced birds are common. Finally, the introduced birds may spread diseases that will attack our native birds. This has happened in Hawaii. In fact, on the main islands of Hawaii, the native birds have been almost completely exterminated. Every bird you seen in the lowlands of Hawaii is an introduced species; the native birds hang on only in isolated mountain forests. We don't want our Samoan birds to share this sad fate.