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Reflected light leading to animal deaths

Reflected light leading to animal deaths

Increasing instances of man-made light sources disrupting natural light cycles and consequently impacting animals that rely on light cues to find mates, determine migration paths and so on are coming to ‘light’.

The most well-known example is that of baby turtles that normally depend on the stars and the moonlight reflected off the surface of the water to find their path from the beach to the sea. Strong artificial lights (street lamps, buildings, etc.) in the vicinity result in the baby turtles heading in the wrong direction towards the brighter lights. Some insects also mistake buildings and man-made structures such as asphalt roads or plastic sheets and oil spills for water surfaces because they appear smooth and dark at night. The primary source of horizontal polarised light (light reflected off surfaces) in nature is water and this is used by animals to locate waterbodies at night. For creatures such as dragonflies, which lay their eggs in waterbodies, this can be fatal. Darker and smoother surfaces reflect light that is more strongly polarised than that reflected by water thereby attracting the animals towards it. It often results in the animal being incapable of leaving the surface as the force of attraction is so great and ultimately leads to injury and even death.

Human-induced polarised light can be offset by undertaking simple measures such as painting white lines on a tar road or hanging white curtains in the windows of dark buildings. “It’s yet another case where we’re faced with a choice between what’s more expensive or what’s better for biodiversity,” says Bruce Robertson, co-author of the study, published in the journal Frontiers in Ecology and the Environment. “Aquatic insects are the foundation of the food web, and what’s harmful to them is harmful to entire ecosystems and the services they provide.”


February 2009


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