Hawaiian honeycreepers are a marvel of evolution. Millions of years ago, some finches arrived on the Hawaiian Islands and began to diversify. As the Pacific Plate moved over the Hawaiian hotspot and new islands formed and others shriveled away, these colorful songbirds evolved into more than 50 species that differed so much in what they ate, where they lived and how they looked that it took scientists quite a while to figure out that they were all related.
More than half of those species are now gone. “Many extinctions took place when the islands were first settled by Polynesian people,” notes Helen James, who, as curator of birds at Smithsonian’s National Museum of Natural History, has studied the birds’ evolutionary history. Then Westerners arrived and bird populations started to disappear more quickly due to a combination of threats, including habitat loss, introduction of invasive species and the arrival of diseases such as avian malaria.
Bird populations on Hawaii’s oldest island, Kauai, have been hit especially hard. Kauai lost at least eight species of honeycreepers — as well as several other “marvelous species” of birds, James notes — before people began keeping good records of the island’s fauna. And now a new study warns that the birds’ situation will get worse — and soon. The honeycreepers that are left on the island are declining fast, and some species could disappear in as little as a decade.
Eben Paxton of the U.S. Geological Survey Pacific Islands Ecosystems Research Center at Hawaii Volcanoes National Park and colleagues looked at population trends for seven species of native forest birds living on Kauai’s Alakai Plateau, the eroded crater of a long-extinct volcano. On other Hawaiian islands, only high-elevation areas have generally been cool enough to keep out the mosquitoes that spread avian diseases. But on lower-lying Kauai, its forests have tended to be cooler than similar-elevation regions on the other islands, so spots such as the Alakai Plateau have been disease-free refuges for native birds.
Or, they were. A 2014 study found that disease prevalence in birds had more than doubled there between 1994-1997 and 2007-2013. Climate change had warmed the plateau enough that disease-laden mosquitoes could spread.
In the new study, Paxton and his colleagues found that six of seven native forest birds surveyed (an eighth proved too wily for scientists to accurately count) are rapidly disappearing and their ranges contracting. All six are honeycreepers, and four are now found only in small, remote parts of the plateau. Fewer than 1,000 Akekee and fewer than 500 Akikiki remain, the team reports September 2 in Science Advances.
“If native species linearly decline at a rate similar to or greater than that of the past decade, then multiple extinctions are likely in the next decade,” the team writes.
James says that she hopes the new findings will be a call to action. “Their data show alarming declines in population and geographic ranges of endemic Hawaiian honeycreepers on the island of Kauai,” she says. The birds’ extinction “would be a tremendous loss.”
Even without avian diseases and climate change, the honeycreepers still face threats from habitat loss, introduced predators and competition with non-native birds (some of whom, such as the Japanese bush-warbler, are thriving on the plateau, the study finds). Reducing those threats could buy the honeycreepers some time to adapt to the growing threat of disease. Scientists can also help by developing genetically modified mosquitoes and figuring out why honeycreepers are so susceptible to avian malaria — and how to protect them from it, James notes.
“The Hawaiian honeycreepers are a classic example of adaptive radiation in animals, second only to Darwin’s finches,” she says. Losing Kauai’s endemic honeycreepers “would definitely cost us in terms of our opportunities to study, understand and appreciate nature.”