A nonnative bird brought to Hawaii to control bugs is threatening endangered native bird species on the Big Island, University of Hawaii at Manoa researchers warn.

The population growth of the Japanese white-eye is limiting the food source of native bird species in the Hakalau Forest National Wildlife Refuge, according to a report by two UH professors published online last month in the journal Current Biology.

Rebecca Cann, a UH genetics professor, said the young of three native and endangered species—akiapolaau, Hawaii creeper and Hawaii akepa—are stunted because they are not getting enough food, making them more susceptible to disease and parasites and less likely to survive.

Fewer than 1,000 akiapolaau and 20,000 of creepers and akepa each remain on the Big Island, the only place in the world where they live, Cann said. The study was completed in a tiny portion of the 40,000-acre refuge on the slope of Mauna Kea, created in the 1980s to conserve endangered forest birds and their habitats. It is managed by the U.S. Fish and Wildlife Service.

Cann and her husband, Leonard Freed, have been studying native birds in the wildlife refuge for more than 20 years. About 10 years ago, they noticed the average size of individual birds had shrunk.

“;It's hard data to get,”; Cann said. “;If we hadn't been working there for so long, it's such a subtle change we might not have noticed what was going on.”;

Cann added, “;It coincided with the number of Japanese white-eyes in the forest.”; The white-eye was brought to Hawaii in the late 1920s as biocontrol agents for bugs. Before the white-eye population increased, the native species had been stable.

The akepa saw the biggest decline, about 15 percent a year, after the white-eye population grew by about 30 percent in the old-growth forest, said Freed, a UH zoology professor.

He suspects the white-eyes are multiplying at a higher elevation in former pastureland where forest management is replanting koa trees. The birds then migrate to the older forest and eat the food of the native species.

Meanwhile, akepa don't live in the reforested area because they prefer hundred-year-old ohia trees that have cavities large enough to nest in.

The akepa are further harmed by the loss of females, Freed said. Akepa mothers can choose the sex of their offspring and usually have males early in the breeding season when food is more plentiful, allowing the young to grow to full size. Smaller females are born later in the season when there is less food.

By the time females are born, however, there isn't enough food for them to survive, he said.

Freed said the solution is to convince the U.S. Fish and Wildlife Service that there is a concern and to control the white-eye population, allowing young individuals of native species to have normal growth and improve their chance for survival.

“;We don't have to take out every white-eye, we just have to knock the number down,”; Cann said.

“;This is not a healthy population,”; she said of the native population. “;It's not a healthy individual level and it's not healthy in long-term odds of persistence.”;