WAILUKU, Maui - The critically endangered Maui parrotbill is apparently doing quite well, perhaps even thriving, in the The Nature Conservancy of Hawaii's Waikamoi Preserve, according a report issued this week.

Nature Conservancy scientists estimated there are about 20 of the chunky yellowish, insect-eating birds per square kilometer in the windward preserve near the summit of Haleakala. That means the estimated population of about 500 is holding steady or possibly even increasing, said Nature Conservancy of Hawaii spokesman Grady Timmons on Friday.

"It was very encouraging because they only have a natural habitat of about 19 square miles, all located in East Maui," Timmons said.

How much the parrotbill population increased is difficult to say, the scientists said, since the last survey was not as extensive. But they said they are certain that the numbers are as good or getting better.

The bird, which is a member of the Native Hawaiian honeycreeper species, has been relegated to the higher elevations since its natural habitat has been damaged over the years by agriculture and development, he said. Avian flu, malaria and rats that eat the birds' eggs also have taken a toll, Timmons said.

Ornithologist Dusti Becker, who is project coordinator for the Maui Forest Bird Recovery Project, said she was surprised by the results of the population survey, which she led.

"I didn't expect that there would be that many birds there," she said.

A previous study had placed the density of the bird population at about half of what the most recent survey found. However, scientists cautioned that the findings were limited to a two-week survey done in September.

Still, the survey area is 400 acres between the Waikamoi Stream and Koolau Gap, and the two-person teams reported hearing or seeing dozens of parrotbills, including juvenile birds.

"We can say with confidence that Waikamoi hosts a breeding population," said Nature Conservancy Maui Director Mark White.

The scientists hypothesized that Nature Conservancy efforts in recent years to fence off the preserve from wild pigs and goats and remove invasive plants and replace them with native species likely contributed to the parrotbill population hike. For instance, native shrub cover in Waikamoi has tripled in the past 15 years.

And the parrotbills mostly eat grubs found in the shrubs' fruit, according to the report.

The Waikamoi Preserve is 5,230 acres. The Nature Conservancy of Hawaii has been managing the property, which is owned by Haleakala Ranch, since the nonprofit received a permanent conservation easement from the ranch in 1983.

About 25 percent of the parrotbill population is found in Waikamoi and most of the rest is in the Hanawi Natural Area Reserve in East Maui, also on the slopes of Haleakala.

The birds were once found throughout Maui and Molokai. The parrotbill is only 5 to 6 inches long and gets its name from the parrot shape of its bill. The birds are olive green on top and have a yellowish belly and distinctive yellow stripe over their eyes.

The bills, which Timmons compared to can openers, are incredibly strong and able to pry open bark to reach insects and grubs.

"The typical story line with endangered forest birds is one of decline," said Sam Gon, The Nature Conservancy's senior scientist and cultural adviser. "To have an endangered bird maintain its population and perhaps even show signs of increasing is very encouraging and cause for celebration."

Nature Conservancy scientists noted that the po'ouli bird, which lived in the same preserve, may be extinct. The last pair of po'ouli birds was last seen in 2004.

For more information, go online to mauiforestbirds.org.