Light Pollution

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Rationale

Following our initial research (2011 - 2015) quantifying Wedge-tailed Shearwater fallout along the southeastern shore of Oahu, we have undertaken a 4-year study to compare seabird mortality along a coastal highway, before and after the switch from yellow sodium bulbs to while LEDs.

It is our hope that these outreach efforts will increase public awareness about shearwater fallout and possible mitigation efforts aimed at reducing mortality.

A Wedge-tailed Shearwater chick, grounded along the Kalaniana'ole Highway, in Waimanalo town, rescued during a road survey.

Approach

In 2011, we initiated a multi-year study of Wedge-tailed Shearwater fallout and road mortality along the southeastern shore of Oahu, working with the U.S. Fish and Wildlife Service and with matching funds from the State of Hawaii DOFAW. Our overarching goal is to document the timing and location of shearwater fallout during the chick fledging season, and to use this this information to educate the public about the threats faced by fledging wedge-tailed shearwaters.

In 2016, we obtained funding to undertake a study to determine whether shearwater fallout changed after the switch of the highway lights from yellow sodium bulbs to white LEDs. To this end, in 2016 and 2017, we completed the following activities:

(i) surveyed a 16-km section of the Kalaniana'ole Highway, from Hawaii Kai to Olomana Golf Course, using standardized methods to map shearwater fallout during the fledging season (Nov. 1 - Dec. 21),

(ii) marked and resighted randomly-selected carcasses at daily intervals to quantify potential biases in the road surveys due to carcass loss by scavenging and washout, and

(iii) disseminated the study results via our project web-site, our facebook site, scientific presentations and public seminars.

Figure 1. The 16-km survey, spanning from the Olomana Golf Course (north), through Waimanalo town, to Hawaii Kai (south). The map shows the location of the Manana shearwater colony and of the Sea Life Park rehabilitation center.

Results

In 2016, we documented 46 downed shearwaters during the fledging season (Figure 2). There was a negative relationship between shearwater fallout and moon phase: with more grounded shearwaters during nights with lower moon illumination (Pearson correlation, r = -0.44).

Figure 2. Wedge-tailed shearwater fallout (relative number of downed birds) encountered during standardized surveys of the study area in 2016. The blue line depicts the degree of lunar illumination, quantified as the mean percent of the lunar disk that was illuminated during the three nights before the road survey.

 

In 2017, we documented 16 downed shearwaters during the fledging season (Figure 3). There was no relationship between shearwater fallout and moon phase (Pearson correlation, r = -0.04).

Figure 3 . Wedge-tailed shearwater fallout (relative number of downed birds) encountered during standardized surveys of the study area in 2017. The blue line depicts the degree of lunar illumination, quantified as the mean percent of the lunar disk that was illuminated during the three nights before the road survey.

 

Overall, after two years of surveys following the shift from yellow sodium lights to white LEDs, we cannot detect a significant change in the magnitude of wedge-tailed shearwater fallout in our study area. Yet, because there is substantial inter-annual variability, an in-depth statistical analysis is needed to assess the influence of the highway lights, in the context of other potential environmental drivers, like the moon cycle and the intensity and direction of the prevailing winds during the shearwater fledging season.

Figure 4.  Abundance of downed wedge-tailed shearwaters documented in the study area, depicted using boxplots (25%, 50%, 75% and 95% of the distributions) and outliers (circles) from 17 annual surveys, spanning November 1 to December 21.

 

Pelagicos Contact

David Hyrenbach

 

Other Pelagicos People

Sarah Donahue, Jenn Urmston

 

Partners

Keith Swindle

US Fish and Wildlife Service
Office of Law Enforcement
3375 Koapaka St., Ste. B-296, Honolulu, HI 96819

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