Bright and early: artificial light affects arrival time, but not group size or vigilance in Little Penguins (Eudyptula minor)

Abstract

Coastal developments are ever-expanding and increasing the use of artificial lights within marine environments. Yet there is conflicting research on the impact of artificial lights on seabirds. Here, we experimentally investigated the impacts of artificial white lights on the behaviours (arrival time, group size, number of groups and vigilance) of breeding Little Penguins Eudyptula minor. Little Penguins are central-place foragers that spend daylight hours foraging at sea and return to their breeding colony after sunset to attend to their chicks or relieve their incubating partners. We exposed Little Penguins returning to their colony at night to either (1) a self-sustaining white LED floodlight or (2) a control system with a decoy light turned ‘off’. We used two different landing sites (site 1, site 2) that differed in landscape characteristics to assess whether behavioural responses to light were site-specific. Little Penguins arrived in larger groups at the landing site 2. Regardless of site, we observed fewer groups that arrived earlier when the light was ‘on’. The effects of artificial light (or ‘lack of artificial light’) on the vigilance of Little Penguins were site-specific, with Little Penguins spending proportionally more time in vigilance when the light was ‘off’ at site 2 compared with site 1. Our results support the idea that artificial lights produced from coastal developments can alter penguin behaviours, but that the effects of artificial lights can be context-dependent and need to be assessed on a case-by-case basis.