Clara Leutgeb

Does light pollution affect wild birds?

An experiment on blue tits (Cyanistes caeruleus) in the Viennese Forest

In the last decades it has been found out that artificial light does not only bring comfort but that there might also be a toll to pay and the term “light pollution” was coined. Birds are especially vulnerable to light pollution because their whole life cycle heavily depends on a fine-tuned synchronisation with seasonal events. So far mostly correlative evidence has been gathered on how their behavior is altered under the influence of artificial light, but what we still do not know is how severe the indirect impact of light is and whether it also translates into the next generation, which is of great conservational relevance. This study sought elucidating these pressing questions using a nest box population of the blue tit (Cyanistes caeruleus) in the Viennese Forest, Austria. Breeding phenology and fitness parameters are compared between birds breeding near streetlamps, experimental LED lamps or without manipulation. To our knowledge, this is the first experimental study to investigate the effects of light at night on reproductive decisions, breeding success and offspring quality at the same time. Artificial light did neither lead to an earlier onset of egg laying nor to a reduced number of eggs, hatchlings, hatching success or fledglings. Also an invasive test (PHA-challenge) for indirect immunocompetence of offspring did not reveal significant differences. Condition, however, was significantly lower in nestlings growing under the influence of LED lamps. Although the effect is minor, this study shows that negative consequences are detectable at close inspection. Nevertheless, the blue tit is less affected by light pollution than expected, probably due to a combination of certain traits: it is a cavity-nesting bird, rather late riser in the morning, and well urbanized. These factors render the species very adaptive which is why I suggest to compare the findings with another less hemerobic bird species in order to thoroughly investigate the subtle and time-delayed effects of light pollution on breeding behavior and reproductive success.

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