The recent death of one extremely rare Hawaiian forest bird appears to have ended any hope of saving the critically endangered species. The only po'ouli in captivity died Friday at the Maui Bird Conservation Center.

Although two po'ouli are believed to remain in the wild, neither has been seen for almost a year.

"We may not have lost just a bird, but one of the last remaining vestiges of a species," said Alan Lieberman, avian conservation coordinator for the Zoological Society of San Diego's Center for Reproduction of Endangered Species, which operates the conservation center. "It is difficult to realize that our last efforts to save this species rely on just two birds."

A small black and gray songbird with a black mask, the po'ouli, which means black head in Hawaiian, is part of the Hawaiian honeycreeper family.

The species was only first discovered in 1973 and was listed under the Endangered Species Act the following year.

The decline - and probable extinction of the po'ouli - is largely the result of habitat loss and introduced species such as feral pigs, rats, cats and mongoose.

University of Hawaii students discovered the po'ouli 31 years ago while conducting research in the Hana rainforest. (Photo by Paul Baker courtesy U.S. Fish and Wildlife Service)

Officials said they are not yet certain what killed the captive male, but it had recently contracted avian malaria - a mosquito-borne disease not native to the Hawaiian Islands.

The bird had been at the conservation center since September, when it was captured as part of an effort to bring all three remaining po'ouli into a captive breeding program.

The captive bird was known to be at least eight years old - considered advanced for the species - and was missing one eye.

Scientists originally suspected it was a female, but definitive DNA testing revealed the bird was a male.

Catching the bird proven a long and arduous task for the Maui Forest Bird Recovery Team, which is made up of a team of ornithologists supported by the U.S. Fish and Wildlife Service and the Hawaii State Department of Land and Natural Resources.

The team first began efforts to catch the birds in February 2003, but struggled to capture the elusive po'ouli.

Biologists aim to continue efforts to locate the remaining birds, which are believed to be a male and a female.

"Although we have not seen or heard them for many months, it may be that they have shifted their home ranges," said Eric VanderWerf, Hawaiian bird recovery coordinator for the U.S. Fish and Wildlife Service. "All of the birds are old for forest birds, but birds have been resighted after long absences in the past, and we are not willing to give up all hope yet."

Biologists fear the little masked bird could be gone forever. (Photo courtesy Hawaiian Division of Forestry and Wildlife)

Thirty-two bird species that breed primarily on islands in the Hawaiian chain are listed on the global IUCN Red List of threatened species, several of which have not been seen in decades and may already be extinct.

More than 20 Hawaiian bird species have gone extinct since 1500 due the combination of habitat loss, non-native predators and introduced diseases.

"Hawaii's bird extinction crisis is a global tragedy that is largely being ignored," said Dr. George Fenwick, president of American Bird Conservancy. "That the world's wealthiest nation is allowing bird extinctions to continue, largely unchecked, in its own back yard is unconscionable."

There is growing evidence that conservation measures within the United States - and the world - are failing.

The world faces a wave of extinctions prompted by unfettered human growth and development. Scientists estimate the current extinction rate is 100 to 1,000 times the natural level.

The most recent Red List released late last month by IUCN - The World Conservation Union indicates that 12 percent of all bird species, 23 percent of all mammal species, and one-third of all amphibian species are threatened with extinction.

The Nature Conservancy warns that some 550 species have gone extinct in the United States in the past 200 years and 4,000 known U.S. species face the danger of extinction.

A report released in October by the National Audubon Society found one-third of U.S. birds are in "statistically significant decline."