Streetlights Disrupt Night-Time Sleep in Urban Black Swans

Abstract

Artificial light at night could have widespread and detrimental impacts on sleep. To reduce disruptive effects of artificial light on sleep in humans, most smartphones and computers now have software that reduces blue light emissions at night. Little is known about whether reducing blue light emissions from city lights could also benefit urban wildlife. We investigated the effects of blue-rich (white) and blue-reduced (amber) LED streetlights on accelerometry-defined rest, electrophysiologically-identified sleep, and plasma melatonin in a diurnal bird, the black swan (Cygnus atratus). Urban swans were exposed to 20 full nights of each lighting type in an outdoor, naturalistic environment. Contrary to our predictions, we found that night-time rest was similar during exposure to amber and white lights but decreased under amber lights compared with dark conditions. By recording brain activity in a subset of swans, we also demonstrated that resting birds were almost always asleep, so amber light also reduced sleep at night. We found no effect of light treatment on total (24 h) daily rest or plasma melatonin. Our study provides the first electrophysiologically-verified evidence for effects of streetlights on sleep in an urban animal, and furthermore suggests that reducing blue wavelengths of light might not mitigate these effects.

Light and noise pollution impacts specialist wildlife species disproportionately

“…Studies of sensory function during sleep in wildlife are sparse; however, new studies are suggestive of impacts from both noise and light given the important role of hearing as a crucial alerting function during sleep and because light exposure appears to influence multiple physiological systems. Light disrupts the intensity, continuity and length of sleep in birds (Aulsebrook et al 2020a,b) and noise appears to fragment and degrade sleep in birds much as it does in humans (Connelly et al 2020). Thus, additional work is necessary to understand whether the costs of noise and light exposure are greater for nocturnal or diurnal species.…”

Light, Sleep and Performance in Diurnal Birds

“…Some birds, such as great tits ( Parus major ), are too small to bear the weight of even the smallest EEG data loggers [ 43 ]. Others, such as water birds, live in environments where successfully deploying and retrieving data loggers is challenging [ 44 ]. Although advances in technology are gradually overcoming these issues, existing studies have often relied exclusively on behavior to characterize avian sleep.…”

“…The findings for geese were partially supported by a subsequent study [ 63 ], which found decreased non-REM sleep during a full moon in winter, but not in summer. In another study conducted during summer, Aulsebrook et al [ 44 ] also found no effect of the lunar phase on the total amount of sleep in black swans ( Cygnus atratus ). This latter study on swans used activity as a proxy for sleep (non-REM and REM sleep combined) after validation with recordings of the EEG, such that it was not possible to distinguish between non-REM and REM sleep.…”

“…However, during a full moon, sleep in geese did not vary with cloud cover, likely because the light from artificially illuminated clouds was similar to moonlight. Numerous studies also found that when exposed to artificial light at night, birds show increased activity [ 44 , 55 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ], delayed chirping behavior [ 74 ], increased vigilance [ 75 ] and reduced sleep behavior at night [ 43 , 76 , 77 , 78 , 79 ], but see [ 80 , 81 ]. There is some evidence that these changes in behavior are associated with reduced circulating oxalate [ 66 , 79 ], a biomarker of sleep debt in rats and humans [ 82 ].…”

“…However, pigeons in the same study showed no difference between the two types of light. Likewise, in captive black swans, blue-rich and blue-reduced lighting caused similar reductions in nighttime sleep [ 44 ]. Behavioral studies have produced similarly mixed findings.…”