ABR data reveal declines of Hawaiian Petrels and Newell’s Shearwaters on Kaua’i

A new paper co-authored by ABR Senior Scientists Brian A. Cooper and Robert H. Day illustrates conservation issues being faced by seabirds in the Hawaiian Islands. Populations of Hawaiian Petrels (Pterodroma sandwichensis) and Newell’s Shearwaters (Puffinus newlli) have been declining over the past 25 years, based on counts of both species on ornithological radar and on recoveries of newly fledged shearwaters in the island-wide “Save Our Shearwaters” (SOS) program.

These species are nocturnal and nest in inaccessible colonies high in the inland mountains, which made them difficult to detect and monitor until ABR brought radar and night-vision technology to Kaua’i. ABR conducted the first radar surveys on Kaua’i just after Hurricane Iniki hit in 1992–1993, providing an important baseline for monitoring survey. We added to the timeline in 1999–2001. The radar was used to count the birds as they flew between at-sea feeding areas and inland nesting areas. The night-vision data revealed that the two species moved at different times of the night.

André Raine and others at the State of Hawaii resurveyed our sites in 2004–2010 and 2012–2013. They also analyzed data from the SOS program from its inception in 1978 through 2015, tracking recoveries of fledglings that end up on the ground, mostly around lighted areas, during their maiden flight to the sea from inland nesting colonies. Both the long-term radar data and the SOS data indicate the same thing: the number of birds visiting the inland colonies has declined 78% and the number of young being produced has declined 94% since our original surveys in 1992.

Why are populations of both species declining? There are a variety of reasons, but the biggest change indicates a decline beginning as a result of Hurricane Iniki. That massive storm went right over the island just as young were fledging in the fall of 1992, causing massive property damage and, presumably, damage to mountainous nesting habitat of both species. (Winds were so strong that they blew the leaves off of most trees in many areas.) Add damage caused by predatory Barn Owls, rats, pigs, feral cats, and dogs that now could get into nesting colonies more easily; powerline collisions; and light attraction, and you see that these birds face a serious set of threats that will make population recovery difficult.

Radar surveys, pioneered by ABR scientists 25 years ago, have become the primary population-monitoring tool to determine whether conservation efforts can reverse the population declines of both species on Kauai. We continue to conduct radar surveys throughout the Hawaiian Islands and elsewhere to assist with development, management, and conservation of birds. For more information on our bird movement and ecology services, please visit http://www.abrinc.com/services/wildlife_and_fisheries/

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