Tracking Flights to Investigate Seabird Mortality Induced by Artificial Lights

Abstract

Light pollution causes attraction and/or disorientation of seabirds, leading to mortality events due to multiple threats. This is a poorly understood phenomenon, largely because of the challenge to track seabirds at night from their nests to the grounding light-polluted locations. New tracking technologies can inform about this phenomenon. Here, we used GPS transmitters with remote download to track the flights of Cory’s shearwater Calonectris borealis fledglings from an inland experimental releasing site to the ocean. We released birds assigned to three experimental groups: GPS tagged, tape-labelled, and control birds. We assessed how both intrinsic (such as body mass, body condition, body size, and down abundance) and extrinsic (i.e., flight descriptors, such as distance, straightness, and flight duration, wind speed, or moon luminance) factors influenced light-induced groundings by using two datasets: one including the three groups and another including just the GPS tagged birds (as GPS devices provide unique information). We tested whether the probability of being grounded by artificial lights was related to intrinsic factors. With the use of the whole dataset, we found that birds with a higher down abundance had a higher probability of being grounded. GPS data revealed that the probability of being grounded was positively related to the tortuosity of flights and the overflown light pollution levels. Also, birds with slower flights were more likely to be grounded than birds with fast flights. Tortuosity increased with light pollution levels but decreased with the ambient light of the moon. GPSs with remote data download provided information on birds reaching the ocean, this being a substantial improvement to previous studies requiring recapture of the individuals to retrieve the data. GPS tracks of birds reaching the ocean allowed us to know that some birds overflew coastal urban areas so light-polluted as the landing sites of grounded birds. We provide novel scientific-based information to manage seabird mortality induced by artificial lights.

Moonlight diminishes seabird attraction to artificial light

“…Experimentally released birds flew straighter over light-polluted areas during full moon and were able to reach the ocean successfully (Rodríguez et al, 2022). Yet, during nights with low moonlight, birds were more attracted to lighted areas and were grounded in higher numbers (see the flights of birds NX07393 and NX07402 in animations of Rodríguez et al, 2022). Consequently, there is no support to the hypothesis that inclinations of birds to fledge are reduced during the full moon.…”

Impacts of artificial light at night in marine ecosystems—A review

“…Thus, determining distances at which individuals are safe is crucial for managing breeding colonies and corridors between colonies and the ocean for inland breeding species. GPS tracking has revealed that most of Cory's shearwater Calonectris borealis fledglings are grounded on areas distant <16 km from their nests (Rodríguez et al, 2015(Rodríguez et al, , 2022.…”

A path forward in the investigation of seabird strandings attributed to light attraction

“…This hypothesis originated from observations of fledgling shearwaters, petrels, and puffins wandering lighted areas or flying into buildings in coastal towns and cities after leaving their colonies for the first time (Hadley, 1961 cited in Reed et al, 1985; Swales, 1965; Sincock & Swedberg, 1969; Imber, 1975; Harris, 1982). Individuals have also been observed circling artificial lights (Montevecchi, 2006), and Global Positioning System (GPS) tracks of Cory's shearwater ( Calonectris diomedea ) fledglings have shown them flying to areas of increased light emittance instead of out to sea (Rodríguez et al, 2015; Rodríguez et al, 2022). Modeling has suggested that patterns of fallout of Newell's shearwater ( Puffinus newelli ) fledglings on Kauai, Hawaii (from rescue program data) were related to regional patterns of overall light intensity (Troy et al, 2013).…”

“…How do fledging behavior and stranding behavior differ between species that nest inland versus coastally? Some researchers have begun addressing these questions using GPS tracking technology (Rodríguez et al, 2015; Rodríguez et al, 2022), manual observation augmented by visible markers (Syposz, Padget, Wynn, et al, 2021), and thermal imagery (but so far only in adults; Syposz, Padget, Willis, et al, 2021). We suggest more widespread uptake of these methods as well as radar and night vision technology to study fledging and stranding behavior of nocturnally fledging seabirds.…”