It has been recently estimated that at mid-high latitudes more than 23% of land surfaces are exposed to artificial light at night (ALAN) ( Falchi et al., 2016). The alteration of natural light levels in the outdoor environment due to artificial light sources, defined as light pollution ( Cinzano et al., 2000), is a globally expanding phenomenon with an estimated increase of 6% per annum ( Hölker et al., 2010). This result shows that there can be positive, indirect effects of ALAN for breeding song birds which may balance against the negative direct effects shown in previous studies. This difference strongly suggests that the lower DEE under white and green ALAN sites is a consequence of higher food availability in these treatments. However, food availability under white and green light was much higher compared to red light and the dark control.
Differences in chick provisioning activity did not explain this result, as neither visit rates nor daily activity timing was affected by light treatment.
Contrary to our expectations, birds feeding their offspring under white and green ALAN showed lower DEE compared to birds in the control dark treatment. We measured DEE of our focal species, the great tit ( Parus major), using a novel doubly labeled water technique that uses breath rather than blood samples. This setup was replicated in eight locations across the Netherlands. We tested the hypothesis that ALAN increases DEE using an experimental setup where four previously unlit transects were illuminated with either white, green, or red LED light, or left dark as a control treatment. Other factors regulating DEE, such as provisioning behavior and food availability, might also respond to ALAN and thus indirectly affect DEE. Previous work has suggested that birds exposed to ALAN show higher levels of provisioning and nocturnal activity, suggesting that white ALAN increases DEE. DEE is a potent mediator of life-history trade-offs and fitness and thus an important aspect to consider when examining the potential long-term ecological effects of ALAN. In birds, effects of ALAN on activity levels are reported for several species and, hence, their daily energy expenditure (DEE) may be affected. Yet, we have limited knowledge on the impact of ALAN on wild species, and on the potential to mitigate any negative effects by using different light sources and colors. The ecological impact of artificial light at night (ALAN) is an increasingly recognized process that accompanies expanding urbanization. 3Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, United Kingdom.2Department of Biology, University of Nevada at Reno, Reno, NV, United States.1Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, Netherlands.
Visser 1, Kamiel Spoelstra 1 and Davide M.
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