Scientists have long documented the drastic decline of Hawaii’s only two endemic seabirds, the Newell’s shearwater and Hawaiian petrel.

From 1993 to 2013, the shearwater population plummeted 94 percent and the petrel population fell 78 percent. Now critically endangered, they are almost exclusively found on Kauai.

The two species hadn’t been found on Oahu since the late 1700s, just before Europeans arrived. But that may be changing.

In a study published Tuesday in the journal The Condor: Ornithological Applications, researchers with Pacific Rim Conservation detailed their discovery of Newell’s shearwaters on the leeward slopes of Mount Kaala in the Waianae Mountains and at Poamoho in the Koolau Mountains. They also detected Hawaiian petrels on the windward slope of Mount Kaala.

Led by Lindsay Young and Eric VanderWerf of Pacific Rim Conservation, based in Honolulu, the team first determined what habitat on Oahu might be suitable for these seabirds by looking at survey data from Kauai and Maui.

The team set up acoustic recording devices at 16 sites on Oahu in 2016 and 2017. Petrels, or ‘ua’u in Hawaiian, were heard at one site and shearwaters, or ‘a’o, at two sites.

“We were doing a statewide survey for these species for the U.S. Fish and Wildlife Service as part of recovery action planning, but Oahu was not initially included as one of the sites to survey, since evidence suggested they weren’t there,” Young said.

“Since we’re Oahu-based, we thought we would at least put a few recording units out to see if there was anything,” she said. “And we were surprised, to say the least, that we not only had calls detected, but detected both species across two years.”

The scientists aren’t sure yet if the seabirds they detected are survivors from past populations that lived on Oahu or if they are young birds from other islands looking for new mates and breeding sites.

“Either way, it gives us hope that we will be able to use social attraction — that is, using calls and decoys — to attract them to nest on an island where they were once abundant,” Young said.

With the seabirds facing myriad threats, from hurricanes and lost habitat to artificial lights and invasive animals, the scientists said having a population of petrels and shearwaters on Oahu would provide insurance for the species’ survival.

Read the full study below.