Wednesday, December 16, 2009

Rare native forest bird holding its own; maybe recovering

The Maui Parrotbill, a critically endangered insect-eating forest bird, appears to be holding its own within The Nature Conservancy's actively managed Waikamoi Preserve in the forested uplands of East Maui.

(Image: Maui parrotbill. Source: The Nature Conservancy.)

Scientists are quick to caution that the information is limited to a two-week survey conducted in September of this year, but results suggest that the chunky yellowish bird's numbers are as strong or even stronger than in previous counts.

“The typical storyline with endangered forest birds is one of decline. To have an endangered bird maintain its population and perhaps even show signs of increasing is very encouraging and cause for celebration,” said Dr. Sam Gon, the Conservancy's senior scientist and cultural advisor.

It is a big deal in a world in which the primary direction of many Hawaiian native forest birds is toward extinction. The rarest of them, the po‘ouli, may be extinct. Its last two members have not been seen since 2004 (Maui Forest Bird Recovery Project).

“For populations of an endangered forest bird to remain somewhat stable for nearly 30 years is encouraging,” said the Conservancy’s Maui program director Mark White.

The rare bird survey was led by Dr. Dusti Becker, an ornithologist and project coordinator for the Maui Forest Bird Recovery Project. Her team estimated that there are about 20 parrotbills per square kilometer of forest between Waikamoi Stream and the Ko‘olau Gap, on the windward slope of Haleakalā.

“I didn't expect that there would be that many birds there,” Becker said. A previous survey had placed the density at less than half that number.

The 5 to 6-inch long birds are olive green on top, yellowish beneath and have a distinctive yellow stripe over their eyes. Their name comes from their short, powerful beaks, which they use to pry open bark and twigs to reach insects and grubs. They are now found at elevations about a mile above sea level, and the U.S. Fish and Wildlife Service estimates that only around 500 individual birds survive.

The birds, once more widespread on Maui and also on Moloka‘i, are now only found on Maui, and only within a range of 19 square miles on the high windward slopes of Haleakalā. More than a quarter of the known habitat for the parrotbills is within Waikamoi Preserve. Much of the rest is within the state's Hanawi Natural Area Reserve, where parrotbills occur at a density of about 40 per square kilometer.

The iconic crested honeycreeper, which is also endangered but is more numerous than the parrotbill, was also frequently seen during the bird population study at Waikamoi, Becker said.

In the survey, two-person teams walked numerous trails over a two-week period, stopping at regular intervals to watch for birds and listen for their calls within the 400-acre survey area. They saw or heard dozens of parrotbills, including at least three juveniles.

“We can say with confidence that Waikamoi hosts a breeding population,” White said.

The latest survey suggests a density double that of an earlier count, but the paper warned that the previous count was limited in scope, and may not have accurately represented the actual population. Still, it is possible that removal of pigs and improvement of the understory vegetation growth—which parrotbills use for feeding habitat—has increased population size at Waikamoi.

The Nature Conservancy has been actively managing the 5,230-acre Waikamoi Preserve since acquiring a permanent conservation easement to the property in 1983, from Haleakalā Ranch.

Since that time, the Conservancy has fenced out pigs, removed alien plants and increased native plants that forest birds and other species depend on. A recent vegetation survey in another portion of the preserve found a three-fold increase in native shrub cover over the past 15 years.

That's a good thing for parrotbills, for whom more native shrubs means more food. Their main feeding technique is prying insects and grubs out of dead branches and fruit and the bark of native shrubs and trees.

Becker said their preferred food sources appear to be grubs from the fruit of the native shrub kanawao, and insects and grubs from the dead branches of ‘ōhelo and ‘ākala. They also pull insects and grubs from the bark of ‘ōhi‘a and koa trees, lichen and any woody, rotting surface.

“At Waikamoi, my sense is that it's a growing population, fundamentally because of forest recovery,” Becker said.

If the population is growing, there is some hope of continued increase, since the recovery of the Waikamoi undergrowth is not complete. The forest understory is still more open than in the prime parrotbill habitat at Hanawi.

For more information:

The Nature Conservancy's Waikamoi Preserve:

On the Maui Forest Bird Recovery Project:

© The Nature Conservancy

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