By Naomi Sodetani

For the first time in decades, wedge-tailed shearwaters are establishing a new colony on Moloka'i at The Nature Conservancy’s Mo’omomi preserve.

The shearwaters' return, says state wildlife biologist Fern Duvall, is due to the Conservancy’s weed and predator control efforts, which are creating a hospitable refuge where the birds can now safely nest and rear their young.

“They’re definitely increasing, no doubt about it,” said Ed Misaki, director of the Conservancy’s Moloka‘i program. “Back in 1999 when the birds first started arriving, there were three nests. This year we counted 307.”

Safe Nesting Grounds

Wedge-tailed shearwaters — or ‘ua‘u kani — are large, dark-brown migratory birds with a black-tipped dark-gray bill. The birds live all their lives at sea and come ashore only to breed. Returning to the same nest site each year, wedge-tails nest in shallow sand burrows, one to two meters in length.

Seabirds like shearwaters travel great distances across oceans, bringing vital marine nutrients back to the land. But shoreline development and predation by non-native species like rodents, cats, mongoose and dogs have deprived them of their natural coastal nesting grounds throughout Hawai‘i.

“Shearwaters are all but gone from the main Hawaiian Islands,” says Duvall. "They can only breed on predator-free islands."

The Conservancy's Mo‘omomi preserve is a rare, intact coastal sand dune ecosystem that in earlier times hosted a wide variety of sea and land bird species. But ground nesting had all but disappeared by the time the Conservancy began managing the area in 1988. Then, in 1999, Moloka‘i staff discovered three sand burrows and began implementing year-round monitoring and protection strategies.

Weed, Predator Control 'Crucial'

Duvall has helped the Conservancy take these annual nest counts since 2000, and also bands chicks as they mature. Each band is numbered, and the data is entered in an international database to track species demographics.

These annual nest counts show the new colony is clearly thriving: from the initial three in 1999 to 17 nests in 2000, to more than 100 nests by 2004. In 2005, 254 nests were counted.

According to Duvall, the weed and predator control efforts were the “crucial step.” Large stands of kiawe have been removed, allowing for natural regeneration of the native plants in the area. Predator monitoring and control efforts prevent feral cats, rats and mongoose from preying on eggs, chicks and adults. And trails have been re-routed away from nesting areas to minimize human disturbance and the risk of crushed burrows.

When the shearwater protection project began, Misaki thought, “Wow, so many cats! As we cleared away the brush, we found lots of bird bones and realized that the cats had used the trees as staging areas for their attacks.”

Feral cat predation of native fauna is a growing ecological problem, especially on islands. Arising from stray or abandoned unsterilized pets, feral cat colonies multiply rapidly in the wild and prey easily on smaller animals that had not evolved survival responses to evade these introduced predators. 

Colony Benefits Ecosystem 

Misaki noted that the dramatic, exponential growth in the shearwater population indicates the earlier populations must be recruiting new adults to the safe haven that Mo'omomi now provides. "They're growing much faster than if it was dependent on the eggs laid by the first birds," he said.

"Colony-nesting and the activity of a thriving colony can bring in other birds, including other native or endangered species that have been lost,” Duvall said. “There’s no reason albatrosses couldn’t be repopulated here.”

In October, the biologist will return to Mo‘omomi to band the new generation of fledglings before they take wing for their first foray to sea. The hope is that they will return next year to raise their young.

When they do, they will bring back important marine nutrients to the land. Duvall explained that seabirds literally fertilize their birthing grounds with nitrogen-phosphate-rich guano (feces), fish and squid fed to chicks, and their very bodies when they die.

“Seabirds benefit the greater health of the coastal system as a whole,” Duvall said. With their presence, “plants become far more vigorous, reinstating ecosystem function that has been lost." 

Future Looks Bright 

At night, during the breeding season, which spans from March to December, a pair will sit head-to-head vocalizing with two-part wailing duets. This poignant cry inspired their Hawaiian name, ‘ua‘u kani, which means, “calling or moaning petrel.”

The outlook for the swelling ranks of wedgies and the habitat they have reclaimed is anything but mournful, however.

“It’s great to see to see this special place successfully restored,” Duvall said. “And so important, getting seabirds back where they belong.”

Nature picture credits (top to bottom, left to right): © Dewitt Jones (sand dunes of Mo'omomi; sand burrow); © Kathy Tachibana/TNC (wedge-tailed shearwater chick in burrow).