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Radar reveals steep declines in Kauai’s seabird populations

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Credit: A. Raine

The island of Kauai is home to two endangered seabirds, the Hawaiian Petrel and the Newell's Shearwater. Monitoring these birds, which are nocturnal and nest in hard-to-access areas, is challenging, but observing the movements of birds via radar offers a solution. A new study from The Condor: Ornithological Applications takes a fresh look at two decades of radar data–and comes to worrying conclusions about the status of both species.

To assess the population trends and distribution of the birds in recent decades, Andr√© Raine of the Kauai Endangered Seabird Recovery Project and his colleagues examined past and contemporary radar surveys as well as data on the numbers of shearwater fledglings rescued after being attracted to artificial lights. Their results shows continuing population declines in both species over the last twenty years–a 78% reduction in radar detections for Hawaiian Petrels and a 94% reduction for Newell's Shearwaters, with the shearwater decline mirrored in decreasing numbers of recovered fledglings over time.

For shearwaters, this is consistent with previously published work, but past analyses of petrel radar data suggested their population was stable or potentially increasing. The researchers attribute the difference to the fact that for this new study, they carefully standardized the data based on sunset times, which ensured that the time periods (and thus bird movement periods) under consideration remained constant from the beginning to the end of the survey period. They believe that the steep declines may have commenced in earnest in the aftermath of Hurricane Iniki in 1992, which led to permanent ecological changes such as the opening of new routes for invasion by exotic predators and plants, as well as significant infrastructure changes across the island.

"These seabirds face a wide range of threats," says Raine. "Conservation effort needs to be focused on reducing power line collisions, fall-out related to artificial lights, the control of introduced predators, and the overall protection of their breeding habitats. Many of these efforts are now underway on Kauai, and I am hopeful that these will continue and expand over the next few years. Ultimately, the conservation of the breeding grounds of endangered seabirds on Kauai is actually the conservation of our native forests and watersheds, with far-reaching benefits for other native plants and birds that rely on these habitats, as well as–ultimately–ourselves."

"It is important to publish this information so that everyone can better understand the severity of the declines in these species and the threats they face," agrees Pacific Rim Conservation's Eric VanderWerf, an expert on Hawaiian seabirds. "We need to consider these data in order to make informed decisions about the best conservation measures."

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"Declining population trends of Hawaiian Petrel and Newell's Shearwater on the island of Kaua'i, Hawaii, USA" will be available June 7, 2017, at http://americanornithologypubs.org/doi/abs/10.1650/CONDOR-16-223.1 (issue URL http://americanornithologypubs.org/toc/cond/119/3).

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists' Union in 2016 to become the American Ornithological Society.

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http://americanornithologypubs.org/

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