Artificial light has long been known to affect animals, plants, and microorganisms. However, most studies have focused on individual species. Now, a new analysis has collected data on avian behavior across more than 500 species, providing confirmation of the broad repercussions of this type of pollution.
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Nighttime light sources can affect plant growth, the way dung beetles navigate, and even human creativity. More than 80% of the world’s population now live in light polluted skies, a figure that rises to 99% in more densely populated regions like Europe. Bird species are exquisitely attuned to changing light patterns, especially during the breeding season.
Now, a new study of more than 500 species offers definitive evidence that birds that are active during the day sing later into the night when they are in proximity to significant light pollution – known as Artificial Light at Night (ALAN).
While the effect has previously been recognized in individual species, two American scientists have now assembled a comprehensive synthesis of ALAN effects across species, space, and season. Brent S. Pease, Assistant Professor in Forestry and Horticulture at Southern Illinois University and Biologist Neil A. Gilbert of Oklahoma State University assessed the impact of light pollution on bird calls using a global acoustic dataset of more than 60 million detections, representing 583 diurnal bird species. They analyzed data gathered from around the world, comparing more than 180 million bird vocalizations in a single year with global satellite imagery.
“We were shocked by our findings: Under the brightest night skies, a bird’s day is extended by nearly an hour,” Pease said in a statement.
Their findings, published last week in the journal Science, found that, on average, light pollution prolonged vocal activity by 50 minutes. However, the impact varied depending on the specific characteristics of the species. Light pollution responses were strongest for species with large eyes, as well as those that nest in the open. Additionally, migratory birds and those with large ranges during the breeding season were more affected.
“Light pollution disrupts light–dark cues that organisms use as timetables for life,” according to Sacha Vignieri from Science’s editorial team. “This situation has the potential to widely affect a variety of species because most living organisms have evolved to respond, in one way or another, to the circadian light-dark cycle.”
The project originated from Pease’s effort to engage undergraduates about birds. Two years ago, he installed a computer with an attached microphone to broadcast birdsong in the main campus’ Agriculture Building eight miles north, where his department and others are housed. He then employed BirdWeather, which makes sophisticated recording devices with Wi-Fi, GPS and sensors connected to the BirdNET database and its machine learning from the Cornell Lab of Ornithology and the Chemnitz University of Technology. BirdWeather’s dashboard provided a better visualization of what bird species were in the area.
“We started seeing – in real time – which birds were at Touch of Nature, right in our Agriculture Building,” Pease continued. “I realized that I stumbled upon something really important for wildlife research. All of a sudden, we not only know where species are but how they are behaving 24/7.”
Further study is required to determine whether the impact is positive, negative or neutral on birds. While they might have more time to forage and mate, they may suffer from the ill effects of fatigue.
Wide-Ranging Issue
The past decade has brought further appreciation of light pollution’s range of impacts on biodiversity and human health, but many details are not yet fully understood. The precision of further studies is additionally hampered by changing conditions: from 2012 to 2016, Earth’s artificially lit outdoor area grew by 2.2% per year, with a total radiance growth of 1.8% per year.
However, the growing number of investigations into the topic – over 5,500, with 547 new references added last year – will make further meta-studies possible, providing illumination not only on the impact of this phenomenon but also on possible ways to address it.
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