Pristine white-tailed tropic birds, koa'e kea, nest on high inland cliffs. Slate-backed Newell's shearwaters, ‘a'o, nest in burrows on wooded hillsides.

And now there's the find of a large population of Hawaiian petrels, ‘ua'u, in the small central forest of Lana'i.

These birds had historically been known from the island, but they were believed to be gone due to loss of habitat and predators. But during surveys of areas where landowner Castle & Cooke had been promoting watershed protection, researchers found large numbers of these native seabirds.

In fact, it may be the largest ‘ua'u nesting site on any island.

Wildlife biologists from the state Department of Land and Natural Resources, the U.S. Fish and Wildlife Service and the University of Hawai'i, working with Castle & Cooke, are studying the colony and controlling predators. The burrow-nesting birds are particularly susceptible to cats, rats, mongooses and barn owls.

"We assumed there would be few, if any, birds remaining on Lana'i, but once we started the surveys we immediately realized that we had found something special," said Scott Fretz, wildlife program manager for DLNR, in a press release. "We don't yet know the total number of birds on Lana'i but there appear to be hundreds, if not more, which would make this one of the biggest populations known in the state.

"This discovery indicates that the population there has grown significantly in the last 20 years."

DLNR interim chairman Allan Smith said the state will work with Castle & Cooke to expand areas being protected.

"Castle & Cooke's work to protect the watershed is a great benefit not just for the water resources it provides to the community but clearly for Hawaiian wildlife as well," Smith said.

The discovery poses a clear challenge in the design and maintenance of a major windfarm proposed by Castle & Cooke for Lana'i. The company is working on plans for a $750 million field of wind generators that would ship power to O'ahu via undersea cable. Conventional windmills are cited by opponents of such structures as a threat to migrating birds.

It is not clear yet whether it would be possible to site wind generators out of petrel flight paths, or perhaps to manage the windfarm in a way that warns the birds away from danger. On Kaua'i, researchers use radar to identify flight paths of ‘a'o.