Ecological Effects of Light Pollution: How Can We Improve Our Understanding Using Light Loggers on Individual Animals?
Light pollution has become an important theme of both scientific research and policy-making. Although in recent years we have seen a boost of research on this topic, there is still surprisingly little knowledge on the levels of artificial light at night that wild animals really experience. I made use of miniature light loggers attached to individual free-living European blackbirds (Turdus merula) to measure the light intensity to which these birds are exposed to in forest and urban areas. I have first shown that male blackbirds living in a city are indeed exposed to higher levels of light at night compared to forest conspecifics, but these levels are substantially lower to what can be measured underneath typical street lamps. Recently I have offered new perspectives by estimating the subjective day length to which urban and rural blackbirds are exposed to and by analysing the overall light intensity to which blackbirds are exposed daily. In a series of studies, I have interpreted these data in the context of daily patterns of activity as well as seasonal biology. European blackbirds which were exposed to a longer photoperiod than their rural counterparts extended their activity into the night and showed reduced levels of melatonin production in the early morning, suggesting that this could be the biophysical process underlying the early onset of daily activity, but also the advanced breeding season observed in many avian species that successfully colonize urban areas. Indeed, I found a remarkable similarity between the difference in the photoperiod experienced by rural and urban blackbirds and the difference in timing of reproduction and onset of daily activity between my two study populations. I will discuss these findings and underlie several outstanding questions that still remain unresolved.
KeywordsBirds Light at night Light loggers Light pollution Urbanisation
I first would like to thank Jesko Partecke and Barbara Helm for invaluable supervision and support throughout my years as a PhD student and young postdoc. I acknowledge the help, support and input originated from discussions with several people including Michaela Hau, Tim Greives, Catarina Miranda, Adam Fudickar, Till Roenneberg, Martin Wikelski, Bart Kranstauber, Marcel Visser, Kamiel Spoelstra and many others. Bruno Erne and Georg Heine have provided me with exceptional light loggers in a very brief time. Last but not least, I acknowledge that the initial idea of using light loggers on individual free-living birds is ownership of Prof. Eberhard Gwinner, whom I never met but whose legacy has profoundly influenced large part of my work.
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