(CN) – Biologists are hopeful about the future of two endemic and endangered Hawaiian seabird species after a survey team found evidence of their existence on Oahu, where the birds were thought to have disappeared.
Newell's shearwaters and Hawaiian petrels nest in colonies on steep mountainous slopes where they burrow in ferns and tree roots or nest in lava or rock crevices. The species have been the focus of major conservation efforts in an attempt to keep them from going extinct, as many other species unique to Hawaii have. Habitat destruction from development and invasive predators that hopped a ride to the islands with explorers and colonists have taken their toll.
A study published Tuesday in The Condor: Ornithological Applications offers hope of previously undetected colonies of these birds on the island of Oahu. Shearwaters and petrels are known to breed predominantly on the islands of Kauai and Maui with some evidence of nesting also on Hawaii, Molokai and Lehua. But both were believed to have extirpated from Oahu prior to European contact in 1778, and between 1993 and 2013 their overall populations plummeted 94 percent and 78 percent, respectively.
Pacific Rim Conservation researchers used spatial modeling to identify potential suitable breeding habitat for both species in order to conduct a statewide survey for the federal government. They then deployed automated acoustic recording units to 16 sites to listen for the birds' calls in 2016 and 2017, accessing remote mountain locations via helicopter.
Despite the longstanding belief that Oahu would yield nothing, surveyors placed a few devices anyway. To their surprise, they detected 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," according to Lindsay Young of Pacific Rim. "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."
Prior to this recorded evidence biologists believed that occasional records from the island involved birds that were thrown off-course at night by city lights or bad weather. Scientists acknowledge these too could be young birds from other islands that are searching for mates and breeding sites, or could be the last survivors of remnant breeding populations on Oahu.
"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.
The Oahu birds could help boost connectivity between individual island populations. Scientists say they also could provide extra insurance in case an island's seabird population is wiped out by a major weather event such as a hurricane.
Despite petrel and shearwater numbers continuing to decline overall, news of breeding on Oahu gives bird biologists a boost of optimism where there had been little to be found in recent years.
Hawaiian folklore tells of shearwaters in such numbers that they darkened the skies in flight. Fossil artifacts point to Hawaiian petrels breeding in sizeable colonies on seven of eight islands.
Adult Newell's shearwaters are dark sooty brown on top with white throat and underparts, and have a hooked tip on a dark bill. They fly direct, fast and low over water, beating their wings rapidly and gliding until they dive into the water to feed on fish. They also swim using their partly folded wings for propulsion.
Hawaiian petrels are uniformly dark grayish black above with contrasting white below and on their throat, forehead and cheeks. They feed on fish or squid by dipping for them while sitting on or flapping just above the water’s surface.
Both species’ parents incubate eggs, brood and feed nestlings.
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