A slice of old Hawaii has returned to the north shore of Molokai in the form of rare coastal sand dunes and the native seabirds that nest there.

The emergence of the once-common Hawaii coastal dune ecosystem is the result of an 18-year campaign by the Nature Conservancy of Hawaii and its volunteers to restore and protect what has become one of the largest wedge-tailed shearwater colonies in the main Hawaiian Islands.

The comeback started in 1999, when a volunteer discovered a couple of shearwater nests near the shore of the 923-acre Mo‘omomi Preserve, apparently the first such nests to be found there in decades.

Now, following years of work clearing tough weeds and battling predatory critters, there are nearly 1,500 active nests and more than 3,200 birds.

And there’s no sign of the colony slowing its growth.

“The birds are a key indicator that something good is happening,” said Wailana Moses, the conservancy’s shearwater coordinator.

The preserve was established in 1988 to safeguard a natural area that has almost two dozen native plant species and is a nesting site for the green sea turtle. There was a time when the Mo‘omomi area was home to at least 30 bird species, but many of those are now extinct, according to the environmental nonprofit.

The dune ecosystem once dominated the West Molokai landscape and nearly disappeared from the main Hawaiian Islands altogether. Today, it thrives at Mo‘omomi, with dunes a mile long and hundreds of feet wide, harboring an array of rare coastal species.

While the shearwater isn’t considered rare in Hawaii, it has disappeared from most areas in the main Hawaiian Islands. Coastal development and predators have exiled the seabirds — known in the Hawaiian language as ‘ua‘u kani — to remote offshore islets and the far-flung Northwest Hawaiian islands.

Ed Misaki, the Conservancy’s Molokai program director, said the 1999 nest discovery was evidence that the shearwaters were trying to establish a colony. The decision was made to start managing the area to encourage its growth.

The nonprofit expanded the available nesting habitat by removing 19 acres of invasive kiawe and launched predator control programs to keep rats, mongoose, cats, dogs and axis deer out of the preserve.

By 2003, there were 98 nests. By 2008, the number had ballooned to 432.

A few years back, a 1.5-mile-long fence was constructed to further isolate the preserve and keep out the high-bounding deer.

“It is a lot of hard work, but it’s worth it,” said Moses, who has overseen weed control at Mo‘omomi for more than a decade.

An ongoing campaign to attach identification bands to the birds twice a year was started in 2005 and is led by Jay Penniman, project manager of the Maui Nui Seabird Recovery Project, and state wildlife biologist Fern Duvall.

Each band is numbered, and data about each shearwater is entered into an international database. The effort aims to track the movement, population and health of the species.

Moses said the banding of adult birds occurs on one night in the spring, when the shearwaters return for breeding. The nesting is monitored in the fall, and banding of the chicks takes place in late October. This year volunteers put bands on 239 new chicks.

New generations of banded birds are returning to the preserve every four to five years, Moses said.

“We will need more and more space,” she said.

The shearwaters live most of their lives at sea, coming ashore only to breed at the same nest site each year. When they do return, their droppings offer nutrients that help plants grow and bring the dune ecosystem to life, scientists said.

Moses said local fishermen know wedge-tail shearwaters as the “aku” bird. When the fishermen see the dark-brown wedge-tails feeding out on the ocean, they know that akule reef fish are down below.

She added that Mo‘omomi is a success because of the help and support from volunteers and partners like the state’s Department of Land and Natural Resources and the Maui Nui Seabird Recovery Project, which helps with the banding.

“We didn’t do it alone, and we will be forever grateful to everyone who helped us ensure that Mo‘omomi will always be a safe haven. It is definitely a biological treasure,” Moses said.