In today's increasingly urbanized world, the lights in many places are always on, and that's having a real impact on the mating life of forest-breeding songbirds, according to researchers.
Keeping the lights on when romance strikes is a definite mood-killer - when it comes to birds, says a new study.
In today's increasingly urbanized world, the lights in many places are always on, and that's having a real impact on the mating life of forest-breeding songbirds, according to researchers.
"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 behaviour, with unknown consequences for bird populations," Kempenaers added.
The researchers investigated the effects of artificial night lighting on dawn song in five common forest-breeding songbirds.
In four of those five species, males near street lights started singing significantly earlier in the morning than did males in other parts of the forest.
Further study of the effects of that behavioural shift on blue tits based on comparison of their reproductive behaviour with and without street lights over a 7-year period showed real consequences. Females near street lights laid their eggs on average a day and half earlier.
And males near lights at the forest's edges were more successful in attracting "extra-pair mates," meaning that they more often sired offspring with females other than their primary social partners.
That might sound like a bonus for those males, but Kempenaers said that doesn't mean it's good for the species, and it might not even be good for the males in question.
"Earlier singing during the morning may come at a cost to males," he said, noting that they may get less sleep and may be at higher risk of predation.
"Second, females are thought to engage in extra-pair copulations with high-quality sires to increase the quality of their offspring. These females may use early singing as a cue reflecting 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. These costs-if they exist-will be hard to measure," he added.
The report has been published online on September 16 in of Current Biology, a Cell Press publication.
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