Accidental introduction of an alien species to Guam created a laboratory for understanding what happens when a species—in this case birds—disappear from an environment. H.S. Rogers, Ph.D., Huxley faculty fellow at Rice University, presented her discoveries at the Environmental Society of America annual meeting August 8 in Portland, OR. In the 1940’s, the brown tree snake, native to Northern Australia and New Guinea, hitchhiked aboard U.S. military planes supplying Guam airbases. By the 1980’s, the tree snakes had virtually eliminated the forest birds of Guam. However, nearby Marianas Islands, without the brown tree snake, still have forest birds. This contrast created a perfect laboratory for Rogers’ investigation of what happens when birds disappear. The effects are both cultural and ecological.
The birds remain an important indigenous cultural resource in the Marianas, the Chamorro on Guam miss the birds for many reasons. An entire generation has grown up without tasting the traditional foods or seeing a native forest bird, the chichirika, (Rufus Fantail) that appears often in Chamorro stories. “The younger generation has given the name Chichirika to the non-native Eurasian Tree Sparrow,” says Rogers. In addition, Guam residents never hear forest birdsong.
Rogers’ study has also investigated the ecological role of forest birds as seed dispersers and as consumers of pests. Although the pest research is still underway, Rogers’ spider counts show population growth of 2 to 40 times the number in comparable locations on islands with birds. Her working hypothesis is that the spiders may be replacing birds as top predators. However, nothing has replaced birds as seed dispersers. Birds eating fruit seeds deposit them far away from the “mother tree.” In addition, birds’ digestive action makes seeds 2 to 4 times more likely to germinate. Loss of the birds has caused two tree species to have a lower number of germinating seeds.
Cautionary tale for U.S. economy
Rogers’ study presents a cautionary tale. Asian Carp are eradicating native species in Midwestern waterways, pythons are changing the Everglades, and the same Styela clava (sea squirt) that has devastated the Australian and English shellfish industry is threatening U.S. East Coast shellfish beds. The tree snakes cannot be eradicated, so the forest birds will never return to Guam. The question is whether the U.S. can stop the spread of non-native species that threaten important economic icons.