Two native seabird species on Kauai appear to be on a collision course with extinction unless conservation efforts can help to reverse a downward spiral in their populations, a new study suggests.
Scientists already know from earlier studies about the substantial decline of the Newell’s shearwater, or ao, and the Hawaiian petrel, or uau, due to a variety of factors, including power line collisions, a perilous attraction to light and predators such as feral cats.
But this new study, to be published Wednesday in the Condor scientific journal, indicates the endangered birds are in worse shape than previously believed.
The study, led by Andre Raine, director of the Kaua‘i Endangered Seabird Recovery Project, shows that populations of the Newell’s shearwater declined by 94 percent and those of the Hawaiian petrel by 78 percent between 1993 and 2013.
Kauai is home to 90 percent of the world’s population of Newell’s shearwaters, listed as endangered on the IUCN Red List of threatened species, and a significant proportion of the Hawaiian petrel, which is listed on the U.S. endangered species list.
The alarming slides in populations were documented in an analysis of radar studies over two decades, in conjunction with 36 years of data from the Save Our Shearwaters (SOS) rescue program, in which volunteers save young seabirds that are attracted to ground-based lighting and crash to earth.
The study also suggests that the damaging power of Hurricane Iniki in 1992 may have a played a role in helping to undermine seabird numbers.
Despite the bad news, Raine said he still thinks the downward trajectory of the seabird populations can be turned around.
“Recent conservation initiatives on the island from a wide range of different organizations, land-owners and entities have shown that people are becoming more and more aware of the perilous state of these birds,” Raine said in a news release. “This gives me hope that we can reverse these spiraling trends.”
Key to the study were results from radar surveys that were started in 1993 by paper co-authors Robert Day and Brian Cooper of Alaska-based ABR Inc. and were continued by the Kaua‘i Endangered Seabird Recovery Project in 2006.
A common tool in the study of birds, radar allows observers to detect the birds in the dark as they fly to and from their breeding colonies and the ocean each summer. With truck-mounted radars parked around the island, operators are able to identify different species by speed, direction and time.
Raine and colleagues examined the radar data between 1993 and 2013 and compared it with the annual islandwide counts of ao fledglings retrieved after being grounded by light attraction from 1979 to 2015.
With the decline in radar-based counts mirroring the numbers recovered by the SOS program, the scientists figure the population has declined 94 percent over the 20 years at an average rate of 13 percent per year.
The SOS data also suggest the decline may have accelerated after Hurricane Iniki smashed into Kauai in 1992.
While it is unlikely that the hurricane itself killed any adults — it slammed into the island during the day while they were out at sea — it could have had “knock-on effects,” according to the study. The powerful storm, for example, likely changed the landscape to open seabird habitat to predators and knocked down trees to expose power lines for new collision opportunities, among other things.
In the 1980s the SOS project was processing on average 1,495 fledglings each year, with a high of 2,235 fledglings in 1987 alone. That number, however, has declined dramatically since then, with an average of only 146 fledglings processed per year since 2010.
Some believe the reason the SOS data is seeing fewer Newell’s shearwater fledglings over time is because of reduced light pollution.
But while some businesses and Kauai County itself have cut back on light pollution, recent analyses of light levels on the island continue to show high levels of artificial light in coastal areas, the study says.
For the Hawaiian petrels, the scientists considered radar counts alone, indicating a 78 percent decline in overall numbers on Kauai.
The study said the large-scale declines are not surprising, considering the significant threats facing both species on Kauai.
And despite several conservation projects benefiting both species, including control of feral cats and power line- and light-minimization projects, significant threats still exist, according to the study.
“With the majority of our radar sites showing massive decreases in numbers of these birds over the years, populations of the birds are in a rapid downward trajectory — particularly in the south and east of the island,” Raine said. “The study highlights just how critical recent conservation initiatives for the species on Kaua‘i are if we are to have a hope of reversing the situation.”
Radar work will continue on Kauai until the middle of July.
The Kaua‘i Endangered Seabird Recovery Project is a joint initiative between the Department of Land and Natural Resources and the University of Hawaii. Radar surveys are funded by a state wildlife grant from the U.S. Fish and Wildlife Service.
