Illuminating Avian Sleep: How Artificial Light at Night Disrupts Memory Consolidation

Abstract: Daily rhythms of light and dark regulate most biological processes and behaviours in animals. These rhythms synchronize internal physiology with the external environment, which is critical for survival. Artificial light at night (ALAN) has become a rapidly growing environmental pollutant, disrupting natural photoperiodic cues and thus interrupting these rhythms. This interruption of the light-dark cycle can adversely impact humans and wildlife, especially by disturbing the sleep-wake cycle. Only a few studies have focused on the impact of ALAN on sleep in wildlife. There is a significant gap in understanding ALAN’s effect on biological processes related to sleep, such as memory consolidation. Our research investigates the impact of ALAN on memory consolidation in black-capped chickadees (Poecile atricapillus), a passerine songbird that relies heavily on spatial memory for winter survival. Since memory consolidation in these birds depends on the hippocampus, we hypothesized that ALAN-induced sleep disruption would impair hippocampal-dependent memory performance. Birds were housed under either natural dark-night conditions (10L:14D) or were exposed to ALAN (10L:14dLAN; 6-7 lux). Birds were then tested on a spatial task (hippocampus-dependent) and a colour-cue task (hippocampus-independent). We found that birds exposed to ALAN performed significantly poorer in both tasks compared to controls, but that ALAN-exposed birds made more working memory errors on the hippocampus-dependent spatial task than on the colour-cue task. Nocturnal video data also revealed increased nocturnal activity and fragmented sleep in the ALAN group, indicating reduced sleep quality. These results suggest that ALAN broadly impairs cognitive function, not only disrupting hippocampal-dependent memory but also affecting other forms of learning. By demonstrating that low-intensity light pollution can degrade sleep and memory in a diurnal species, this study highlights the need to reevaluate how artificial lighting affects the cognition and behaviour of wildlife. Illuminating Avian Sleep: How Artificial Light at Night Disrupts Memory Consolidation DOI: Keywords: artificial light at night; sleep; memory consolidation. Aastha Saini, Gumin Jung, Scott MacDougall-Shackleton 11 2 Department of Biology, Western University; Advanced Facility for Avian Research, Western University, Canada Department of Psychology, Western University; Advanced Facility for Avian Research, Western University, Canada 1 2 Ecological and Biological Responses to Light Pollution 16 Corresponding Author: [email protected]