Lights, Action!

European blue tit, a relative of our American chickadee.

While toxins and noise are often cited for their detrimental effects on wildlife, recent research suggests that light pollution is negatively affecting forest-breeding wildlife as well.

“In comparison to chemical and noise pollution, light pollution is more subtle, and its effects have perhaps not received the attention they deserve,” said Bart Kempenaers of the Max Planck Institute for Ornithology in Germany. “Our findings show clearly that light pollution influences the timing of breeding behavior, with unknown consequences for bird populations.”

By studying forest-nesting birds whose territories are adjacent to illuminated street lights and comparing them to birds breeding in the forest interior, Kempenaers and his colleagues found that males of four out of five common species started singing earlier in the morning when they had a territory near a street lamp. “The [European] robin, for example, is the earliest singing bird in that forest, and the light affected the birds so that they started singing almost an hour and a half earlier on average than they would normally do in the dark part of the forest,” Kempenaers said.

While that may not sound harmful to the birds, the researchers believe that earlier singing may mean the birds get less sleep and therefore are at greater risk of predation.

Over a seven year period, the researchers also found that female blue tits – a species closely related to the chickadee in the U.S. – who made nests near street lights laid their eggs a day and a half earlier than those who nested further from artificial lights. And males near lights were twice as successful at siring offspring with females other than their primary partners. It is believed that females engage in this “extra-pair copulation” with high quality males to increase the quality of their offspring, and the females may use early singing as a cue to indicate male quality. “Light pollution may disrupt the link between the cue – early singing – and male quality, so that females would end up having their offspring sired by lower quality males,” said Kempenaers.

The affects of light pollution on animals has not been well documented, although numerous studies have demonstrated how artificial lights can confuse birds that migrate at night, resulting in many migrants flying into lighted towers. The death of 3,000 re-winged blackbirds this past New Year’s eve in Arkansas, after they became disoriented by nighttime fireworks and collided with buildings and each other, is just a recent example. Kempenaers believes that the effects of street lights on the timing of breeding is not restricted to birds. He also speculates that this effect may increase as birds and other wildlife breed earlier in response to warming spring temperatures. The consequences of such a shift, however, will ultimately depend on whether it creates a mismatch between breeding and the peak availability of food.

Asked whether his research would be applicable to birds in the U.S., he said: “Our findings about the effects on singing behavior are probably generally applicable to all birds that have early morning singing. The effects of timing of laying is also an effect that I suspect to be rather general. The effects on extra-pair mating may be unique to blue tits, however; it would depend on the specific biology of a particular species.”


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