Researchers have found previously unknown colonies of two native Hawaiian bird species on the island of Oahu. The discovery of Newell’s Shearwaters and Hawaiian Petrels comes as a welcome surprise to conservationists after habitat loss and other threats have dramatically driven down the numbers of these two populations.
Between 1993 and 2013, Newell’s Shearwaters declined by 94 percent and Hawaiian Petrels declined by 78 percent. Both bird species were thought to have disappeared entirely from Oahu in the late 1700s.
A team led by Lindsay Young of the Pacific Rim Conservation used a spatial model based on elevation, forest cover, and illumination to identify potential suitable breeding habitat for both bird species on Oahu. In 2016 and 2017, the researchers deployed acoustic recording units across the island to listen for bird calls at 16 different sites. They were surprised to detect the presence of petrels at one site and shearwaters 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,” said Young. “Since we’re Oahu-based, we thought we would at least put a few recording units out to see if there was anything. And we were surprised, to say the least, that we not only had calls detected, but detected both species across two years.”
According to the researchers, the birds may be the last survivors of remnant breeding populations on Oahu, or young birds from other islands searching for 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 nest on an island where they were once abundant,” said Young.
The study is published in The Condor: Ornithological Applications.