Disruptive effects of light pollution on sleep in free-living birds: Season and/or light intensity-dependent?

Abstract

Light pollution or artificial light at night (ALAN) is an increasing anthropogenic environmental pollutant posing an important potential threat for wildlife. Evidence of its effects on animal physiology and behaviour is accumulating. However, in order to effectively mitigate light pollution it is important to determine which factors contribute to the severity of effects of ALAN. In this experimental study we explored whether there are seasonal-dependent effects of ALAN on sleep in free-living great tits (Parus major), an important model species. Additionally, we looked at whether light intensity determined the severity of effects of ALAN on sleep. We therefore exposed animals to artificial light inside the nest box (3lx) in December (winter) and February (pre-breeding season). Results from February were compared with the results from a previous study in February, using a lower light intensity (1.6lx). We found little evidence for a season-dependent response. Effects of ALAN hardly differed between high and low light intensity. ALAN disrupted sleep with as main effect a decrease in sleep duration (≈-40min) as animals woke up earlier (≈-24min). However, compared to a natural dark situation sleep onset was delayed by high but not by low light intensity of ALAN. Our study underlines earlier found disruptive effects of ALAN on sleep of free-living animals. While we found no conclusive evidence for seasonal or light intensity-dependent effects of ALAN, additional experimental work using lower light intensities might show such differences. Examining potential management options is crucial in mitigating disruptive effects of light pollution, which will be an important focus for future studies.

Cavities shield birds from effects of artificial light at night on sleep

“…From a power analysis, it seems that, for example, for awakening time, we would need about double the sample size to obtain an 80% power to detect a 20 min difference in the light treated group. This is an effect size similar to our experimental studies with ALAN inside the nest box (Raap et al., ). We, therefore, recommend experiments with larger sample sizes to validate our results.…”

“…We conclude that our light treatment, in which we experimentally exposed the entrance of the nest box to ALAN (1.6 lux white LED), independent of the rest of the environment, had no effect on great tit sleep, while direct exposure to ALAN does disrupt sleep (Raap et al., ; ). We therefore hypothesize that artificial light at night resulting from street lights may have a limited direct effect on sleep of birds inside cavities during winter.…”

“…Experimental ALAN inside a nest box affected nestling physiology (Raap, Casasole, Pinxten, & Eens, ), but ambient light pollution at the nest box was unrelated to nestling physiology (Raap, Pinxten, Casasole, Dehnhard, & Eens, ). Whether ambient light pollution leads to altered sleep behavior of birds inside nest boxes (cavities), similar to what has been found in experiments with ALAN inside a nest box using free‐living blue and great tits (Raap et al., , , ; Sun et al., ), needs to be examined.…”

“…Light pollution disrupts natural light cycles and potentially poses an important threat for wildlife, biodiversity, and humans (Duffy, Bennie, Duran, & Gaston, 2015;Gaston, Bennie, Davies, & Hopkins, 2013;Hölker, Wolter, Perkin, & Tockner, 2010;Kyba & Hölker, 2013;Navara & Nelson, 2007;Rich & Longcore, 2005), since it results in a wide range of physiological and behavioral responses (see, e.g., Da Silva & Kempenaers, 2017;Dominoni, Quetting, & Partecke, 2013). For example, in two cavitynesting songbird species, blue tits (Cyanistes caeruleus) and great tits (Parus major), sleep behavior was disrupted by experimental light inside the nest box (Raap, Pinxten, & Eens, 2015, 2016cRaap, Sun, Pinxten, & Eens, 2017c;Sun, Raap, Pinxten, & Eens, 2017). Sleep is an important animal behavior with multiple possible functions, enabling animals to recover from daily stress (Siegel, 2009;Weljie et al, 2015), to consolidate memory and to conserve energy (Gobes, Zandbergen, & Bolhuis, 2010; Roth II, Rattenborg, & Pravosudov, 2010;Vorster & Born, 2015).…”

Impacts of artificial light at night on sleep: A review and prospectus

“…Assuming this to be true, birds woke earlier when exposed to higher intensities of light at night. Subsequent studies used LED lights inside nest boxes to experimentally manipulate light at night, and record the effects on sleep behavior using the same definition (Raap, Pinxten, & Eens, ; ; Raap, Sun, Pinxten, & Eens, ; Sun, Raap, Pinxten, & Eens, ). Interestingly, exposure to light at night decreased the duration of night‐time sleep behavior in great tits, but not blue tits (Sun et al., ), and the effects on female great tits were much greater during the nestling period (Raap, Pinxten, & Eens, ).…”