Is This the World's Rarest Bird?

The po'ouli survives only in a few hundred acres of nearly impenetrable rain forest

  • Les Line
  • Dec 01, 1997
With 168 birds on the list of the world's most critically endangered creatures--and many of them from remote, inhospitable places--researchers cannot say for sure which species is the rarest. But that dubious distinction may belong to the po'ouli (pronounced "poh-oh-U-lee"). This Hawaiian honeycreeper, whose name means "black-faced," survives only in a few hundred acres of nearly impenetrable rain forest on the windward side of Maui's Haleakala Crater. At last count, the known po'ouli population was six. And with time running out, experts are scrambling to find a way to save the species from extinction.

If they do succeed, chances are good that Tonnie Casey will be the one who flies to the rescue--literally, at the controls of a Huey helicopter dropping poison bait to eliminate the rats that overrun po'ouli habitat. A biologist for Hawaii's largest private landowner, Kamehameha School's Bishop Estate, Casey has a vested interest in the po'ouli's survival: She was the bird specialist who discovered the species in 1973 while working with college students on an ecological study of what is now the state's Hanawi Natural Area Reserve. But when Casey returned to her native Hawaii after a couple of peripatetic decades that included a long stint of flying choppers for the U.S. Army, she found that the bird had virtually disappeared in her absence.

Black and Pacific rats, which arrived long ago in the Hawaiian Islands as stowaways, have been implicated along with mosquito-borne disease, habitat loss and forest degradation by feral pigs in the extinction of other endemic honeycreepers. At least 11 species have disappeared since the explorer Captain James Cook dropped anchor there in 1778, and another 16 are on the world threatened list, compiled by the IUCN-World Conservation Union.

Mostly forest birds, the honeycreepers evolved from an unidentified finch ancestor into dozens of species. All of them are defenseless against the nocturnal, tree-climbing rats, which raid nests and kill the adults.

"I believe that we can save the po'ouli if we follow New Zealand's example--and do it quickly," says Casey, who is also commander of the National Guard helicopter unit at Hilo, Hawaii. "They've had success using aerial drops of toxicants to create rat-free island sanctuaries for threatened native birds."

New Zealand's spectacular rescue of the Chatham Islands black robin, when only five individuals were left, offers another ray of hope for the po'ouli. Actually a flycatcher rather than a thrush like its American and European namesakes, the black robin was a common bird throughout the remote Chathams group until colonists arrived with cats and rats and cleared most of its scrub habitat. Researchers moved the last survivors to a safe island, manipulated the number of eggs that the black robins laid and enlisted related birds as foster parents. Robin numbers have grown to more than 200.

Biologists at the U.S. Interior Department's Pacific Island Ecosystems Science Center in Hawaii have favored a similar hands-on approach to saving the po'ouli. The plan is to find a nest and move the first clutch of eggs to the Peregrine Fund's new captive breeding facility on the island of Hawaii, where workers have reared and successfully released some common native forest birds and are now experimenting with a few endangered species that are not nearly as scarce as the po'ouli.

However, an intensive search for a po'ouli nest last spring came up empty-handed. Moreover, the Peregrine Fund itself is reluctant to accept po'ouli eggs. "We need more experience with other insectivorous honeycreepers before exposing po'ouli to the risks of egg transport, hand-rearing, imprinting and release," says William Burnham, the organization's president. "We can't afford even one mistake." Aggressive rat control, not captive breeding, is the best conservation strategy, he insists.

Wildlife workers currently use poison bait stations to kill rats, mongooses and other pred- ators in po'ouli habitat. But getting government approval for a helicopter broadcast of an effective rodenticide has been a slow process, in part because state officials fear a public backlash. Authorities want more studies. But, says Burnham, "We needed to do it months ago, before the start of this year's nesting season."

At the center of this tempest is the po'ouli, a stub-tailed bird about the size of a large chickadee and cryptically colored in shades of brown except for its black mask, which is unique in the honeycreeper clan. The po'ouli lives just below timberline on the 10,023-foot volcano in elfin forest, where the limbs of ohi'a lehua trees are wrapped in epiphytic mosses, lichens and ferns and the vegetation is saturated by as much as 550 inches of rain a year. Scientists hope that a few more po'ouli might survive in the lower and most inaccessible part of the Hanawi preserve.

Very little is known about po'ouli biology. Observers have watched the birds hop along tree limbs, tearing apart epiphytes and loose bark with their finchlike bills in search of snout beetles, spiders and other invertebrate prey. They also eat a lot of native land snails. The po'ouli nest is an open cup on a ohi'a lehua branch. The bird's clutch size apparently is two, although no one has ever seen intact eggs.

When Tonnie Casey made her startling discovery 24 years ago, the po'ouli population may have numbered in the hundreds. Although surveys in the mid-1980s indicated that the species was declining, state and federal biologists were stunned when they launched a belated search for the bird in 1994 and "realized the po'ouli wasn't there anymore," says Thane Pratt of the Pacific Island Ecosystems Science Center.

Pratt notes that the Hawaii Department of Land and Natural Resources has fenced most of the Hanawi reserve, a difficult and expensive task, and has removed many of the feral pigs that ravaged the forest understory. But the Interior Department scientist admits that efforts to save the species "should have started 10 years ago. I don't think the po'ouli will make it."

Casey, however, remains optimistic. "The birds still have a chance if we can get the toxicants out there and protect their nests from rats," she says. Adds the Peregrine Fund's William Burnham: "Millions of visitors come to Hawaii and mostly what they see are introduced plants and birds. We've lost more of the nation's biodiversity in Hawaii than in all of the rest of the states." Burham insists that "the po'ouli should not be allowed to just go quietly into oblivion, if we can prevent that end."

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