MO'OMOMI, Moloka'i — A loose dog killed 50 adult wedge-tailed shearwaters Wednesday at a breeding colony at The Nature Conservancy's Mo'omomi Beach Preserve.

The dog was captured roaming the dunes with a shearwater in its mouth, according to the organization.

"We're all devastated," said Ed Misaki, the Conservancy's Moloka'i program director, in a news release. "These were all adult birds trying to establish their nests. This will affect the ability of this thriving seabird colony to continue to grow."

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 and nest at the same site each year. They nest in shallow sand burrows, 3 to 6 feet in length.

According to state wildlife biologist Fern Duvall all 50 of the birds were sexually mature adults and at least 7 years of age. They had recently begun arriving at the preserve to establish their nests for the breeding season, which extends from March through December.

"It's a real tragedy," said Duvall, who has been conducting annual nest counts of the shearwater population at Mo'omomi since 2000. "These are long-term mono- gamous birds that require seven years before they become sexually mature adults. So we have lost a good portion of the breeding population here."

The Mo'omomi Preserve is a rare, intact coastal sand dune ecosystem on Moloka'i's northwest coast. When the conservancy first established the preserve in 1988, shearwaters and other ground-nesting sea birds had all but disappeared. In 1999, three burrows were discovered and a year-round monitoring and predator control program was implemented to protect the birds from rodents, cats, mongooses and dogs.

The organization said the program was so successful that last year the nest count had grown to 418, with a further increase expected this year before the dog attack.