July 9th, 2013 by

About 1,700 years ago, humans first arrived on the scene on the island of Hawai’i. Since then, the island’s biodiversity has steadily declined. This is due to several factors: deforestation, humans repurposing land for agriculture and, possibly most detrimental, the introduction of non-native species. And it’s a non-native species that has put a Hawai’ian bird on the brink of extinction.

Non-native plants and animals have been brought to the Big Island of Hawai’i for a wide variety of reasons. First, Polynesians, who were the first inhabitants of Hawai’i, brought animals and plants for food. In the 18th century, Europeans brought over more livestock and other plants that would go on to out-compete native species. Then, in the 1920s, two devastating invasives were introduced: the banana poka, an ornamental vine that has taken over tens of thousands of acres of forest, and the Japanese white-eye (Zosterops japonicus), a bird introduced to shrink insect populations. It is doubtful that people realized in 1929, when the bird was introduced, that it would also be responsible for shrinking the population of something else, a native honeycreeper.

Japanese white-eye

Japanese white-eye
Credit: Toshihiro Gamo

In a new study released last week in the journal PLOS ONE, researchers from the University of Hawai’i at Monoa reveal that the endangered Hawai’i creeper (Oreomystis mana) population at Hakalau Forest National Wildlife Refuge has shrunk by 63 percent in the last decade, most likely from food limitation associated with increased numbers of the Japanese white-eye. For the last 80 years, the creeper and white-eye have been forced to share food sources on the confined island, and the white-eye has been winning the foraging battle, as its population increased while the creeper’s declined. Beyond the population numbers, though, the study’s authors document that the surviving young creepers have lower body mass, shorter bills and shorter legs than past generations of creepers, and overall, the species is showing signs of malnutrition.

From 1992 to 1996, American Forests planted more than 150,650 trees in Hakalau Forest National Wildlife Refuge to help reestablish nesting ground for Hawai’ian birds. The tree most commonly planted was the acacia koa, a hardwood tree that provides a habitat for birds like the creeper. It is important that these trees be replanted because half of the island’s native forests have disappeared.

These birds have surely seen better days — before humans disrupted their natural ecosystem. Scientists and volunteers on the island are hard at work trying to save both the native forests and native wildlife from the threat of invasive species. For more on this fight and struggle to protect Hawai’i’s native species, check out our Spring/Summer 2013 magazine feature “Islands in the Balance.”