Restless roosts: Light pollution affects behavior, sleep, and physiology in a free‐living songbird

Abstract

The natural nighttime environment is increasingly polluted by artificial light. Several studies have linked artificial light at night to negative impacts on human health. In free-living animals, light pollution is associated with changes in circadian, reproductive, and social behavior, but whether these animals also suffer from physiologic costs remains unknown. To fill this gap, we made use of a unique network of field sites which are either completely unlit (control), or are artificially illuminated with white, green, or red light. We monitored nighttime activity of adult great tits, Parus major, and related this activity to within-individual changes in physiologic indices. Because altered nighttime activity as a result of light pollution may affect health and well-being, we measured oxalic acid concentrations as a biomarker for sleep restriction, acute phase protein concentrations and malaria infection as indices of immune function, and telomere lengths as an overall measure of metabolic costs. Compared to other treatments, individuals roosting in the white light were much more active at night. In these individuals, oxalic acid decreased over the course of the study. We also found that individuals roosting in the white light treatment had a higher probability of malaria infection. Our results indicate that white light at night increases nighttime activity levels and sleep debt and affects disease dynamics in a free-living songbird. Our study offers the first evidence of detrimental effects of light pollution on the health of free-ranging wild animals.

Two sides of a coin: ecological and chronobiological perspectives of timing in the wild

“…A potential measure that can be taken to reduce the impact of light at night, other than simply reducing the amount of light, is to modify the spectrum of the light. For example, blue tits (Cyanistes caeruleus) exposed to green light at night shifted their activity patterns less than those exposed to white light [194]. Lunar cycles are also affected by artificial light at night.…”

The dark side of light: how artificial lighting is harming the natural world

“…Songbirds roosting around the white light were restless through the night, slept less and had metabolic changes that could indicate poorer health 8 . The project also looked at how light affects bats, which have had mixed fortunes under the explosion of artificial illumination.…”

What type of rigorous experiments are needed to investigate the impact of artificial light at night on individuals and populations?

“…In our recent paper on how artificial light at night (ALAN) affects within-individual changes in physiology, we used a unique experimental setup of colored LED lights to show effects on nighttime activity levels and physiology in free-living great tits, Parus major (Ouyang et al, 2017). Raap, Pinxten, and Eens (2017) response, entitled: "Rigorous field experiments are essential to understand the genuine severity of light pollution and to identify possible solutions" lists issues with our analyses.…”

“…Controlling individual light exposure in the field is difficult. In our setup, we solve this problem by including Whether this effect is direct or indirect still needs to be tested, especially if it is used as a proxy for sleep deprivation (de Jong et al, 2016;Ouyang et al, 2017). Currently, there is a paucity of true-to-life field studies, especially ones that measure direct light exposure for free-living animals (Ouyang et al, in review), but there are exceptions (Dominoni, Goymann, Helm, & Partecke, 2013;Knop et al, 2017;Robert, Lesku, Partecke, & Chambers, 2015).…”

“…Workarounds, such as placing light sources inside of nest boxes (Raap, Pinxten, & Eens,, 2015), may result in unrealistic situations that are difficult to interpret. Intraindividual changes in oxalic acid during a period which was preceded by increased nighttime activity is an interesting phenomenon, which we have discussed previously (Ouyang et al, 2017). In our setup, we solve this problem by including Whether this effect is direct or indirect still needs to be tested, especially if it is used as a proxy for sleep deprivation (de Jong et al, 2016;Ouyang et al, 2017).…”