Wildlife confused by polarised light pollution

Catherine Brahic in New Scientist: What do sky scrapers have in common with ponds? The way they polarise light acts as a magnet to some animals, say researchers. This unwanted side effect from some industrial materials – including road surfaces and automobiles – is called polarised light pollution, and Bruce Robertson of Michigan State University says the phenomenon is widespread enough that it is disrupting ecosystems.

When light bounces off smooth, dark surfaces it becomes polarised – meaning the light wave is aligned in one plane. In natural environments, this most commonly happens around water, but humans excel at making smooth surfaces. "Cars, asphalt, oil pools, and windows polarise light more strongly than water," says Robertson.

To animals tuned to distinguish polarised light and use it as an environmental cue, "these objects look more like water than water," he says. "Even when given the choice between water and human-made surfaces, some insects prefer to lay their eggs on – and settle near – the latter."

…The team say at least 300 aquatic insects are likely to be affected by polarised light. Male dragonflies, for example, often perch on car antennas, attracted to the reflective car paint. Female aquatic insects have been found to lay their eggs on car bonnets, cement floors, and roads – where they have no chance of hatching.

A large Yellow-winged Darter (Sympetrum flaveolum) from the side, shot by André Karwath aka Aka, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 2.5 License.