Blue and white light pollution is disastrous for Cory's shearwater fledglings Free

Perfecting the blue LED in 1993, Shuji Nakamura, Isamu Akasaki and Hiroshi Amano, paved the way for a revolution in low-energy street lighting: blue LEDs produce intense white light when partially coated with a phosphor layer. But as humans extinguish the nocturnal darkness with light pollution, wildlife is paying a price. ‘Seabirds are among the most threatened avian species’, says Elizabeth Atchoi from the University of the Azores, Portugal, and some of the most impacted creatures are burrow-nesting shearwater fledglings as they embark on their maiden voyage out to sea. ‘At the end of the breeding season, thousands of burrow-nesting seabird fledglings fall to the ground in urban areas after encountering light-polluted areas’, says Atchoi. The fledglings appear to become trapped, unable to escape the bright light. But how does the colour of nocturnal light pollution impact the youngsters? Are some shades, including blue light, more dangerous for fledgling shearwaters than others? Atchoi and colleagues from Lithuania, Spain, France and the Azores, investigated how white, blue and red light affected the choices of recently grounded fledgling and adult Cory's shearwaters.

Fortunately for beleaguered shearwater youngsters on the Azores island of Faial, SOS Cagarro volunteers – a conservation campaign group – have been on hand every year since the 1990s to scoop up fallen fledglings and deliver them to the organisation's operational centre to recover before sending them safely back out to sea. However, in October and November 2020 and 2021, just before the fledglings resumed their flights, Atchoi and colleagues set 131 of the birds a small test at the top of the cliff from which they were due to depart. Placing each bird in a dark box against the back wall of a small enclosed rectangular arena, the researchers offered the birds a choice between the two sides of the arena when they raised the box. On some occasions one side of the arena was bathed in white light while the other side was completely dark, but on other occasions the fledglings chose between a side illuminated with red light while the other was bathed in blue light. The fledgling then decided which side it preferred to occupy, before walking through and exiting the arena to the cliff edge, ready to resume its journey. In addition, Atchoi tested the preferences of adult shearwaters, briefly removing them from their nests at night before allowing them to wander back to their chicks.

Comparing the fledglings’ and adults’ choices, it was clear that the youngsters much preferred the dark side of the arena; only 6 ventured into the light side, while 20 crossed into the darkness. However, once within the brightly lit side of the arena, the fledglings struggled to leave. ‘They become apparently disoriented by the brightness of the white light’, says Atchoi. In contrast, the fledglings in the dark side exited the arena, ready to resume their departure out to sea. The team also noticed that although the fledglings were keener than the adult birds to move around the arena, it took them longer to decide which side of the arena to move into, possibly because they were bewildered. And when offered the choice between red and blue light, the majority of the fledglings avoided the blue side; only 9 entered the blue half of the arena while 28 fledglings headed to the red side.

Blue light, a significant component of artificial white light, has a naturally disturbing effect on Cory's shearwater youngsters. So, although LEDs have revolutionised street lighting, the whiter light with more blue tones is playing havoc with shearwater fledglings as they venture for the first time from their burrow nests.