Study finds light pollution makes birds sing longer each day

By Stephen Beech

Light pollution makes birds sing for an average of 50 minutes longer each day, reveals new research.

Birds that are active during the day sing later into the night in places with significant light pollution, say American scientists.

They found that light pollution is causing birds around the world to prolong their vocalizations by an average of 50 minutes.

The analysis of more than 500 diurnal bird species showed that birds that are more exposed to light – whether through large eyes or open nests – are the most affected by light pollution.

Scientists know that light pollution, which impacts almost a quarter of the planet, is influencing activity patterns governed by the circadian light-dark cycle in individual species.

The new study, published in the journal Science, is the first to document the phenomenon in birds across species and space and seasons.

Dr. Brent Pease, an Assistant Professor at Southern Illinois University, and Dr. Neil Gilbert, an Assistant Professor at Oklahoma State University, analyzed data gathered from around the world, comparing more than 180 million bird vocalizations in a single year with global satellite imagery.

Dr. Pease said, “We were shocked by our findings.

"Under the brightest night skies, a bird’s day is extended by nearly an hour."

Dr. Pease installed a computer with an attached microphone at Touch of Nature Outdoor Education Centre two years ago to broadcast birdsong in the main campus’ Agriculture Building eight miles north, where his department and others are housed.

What resulted was a basic data dashboard on the Ag Buildings’ monitors.

Dr. Pease 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.

Dr. Pease said: “We started seeing - in real time - which birds were at Touch of Nature, right in our Agriculture Building.

“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.

“For decades, we have been steadily improving our ability to predict where species are and how many individuals there are.

"But BirdWeather unlocked behavioural research at large geographic and time scales.

"We could start to learn, at a scale never before, how birds were responding behaviourally to human forces.”

As trail cameras had revealed around-the-clock mammal behaviour about 25 years ago, he says BirdWeather, along with BirdNET, could now do for birds.

Dr. Pease said: “We are just now entering the golden age of avian conservation, all through machine learning and participatory science."

With BirdNET, the research team used machine learning to convert bird vocalizations to visualizations called spectrograms, with a distinct visual pattern for each bird species.

BirdNET then cross-checked the pattern with spectrograms of more than 6,000 species in its database.

Dr. Pease said: “The machine learning algorithm makes it possible to analyze 24/7 audio recordings, which would otherwise take lifetimes to listen to.

“Neil and I are the first, to our knowledge, to apply and analyze the BirdWeather data in this way.

"We have many research options, but first we focused on how birds are responding to global light pollution, which is a growing concern for humans and wildlife alike.”

Dr. Pease noted that birds staying up an hour past their normal bedtimes was an average, but actual times varied by species.

He said: “The next question was: why?

“What is driving this response by birds? We had the idea that maybe it was a species’ photoreceptor sensitivity – their eyesight. And this turned out to be a key factor.

"Species with large eyes relative to their body size had a disproportionately stronger response to artificial light at night.

"They were more sensitive to light at night than species with small eyes.”

He says whether the impact is positive, negative or neutral will require further study.

Dr. Pease said birds might have more time to forage for food and to mate, but an hour less sleep could be detrimental to their health.

He added, “This is citizen-science at its best.

“A technology designed for people to check out the species in their own backyards has acquired an unprecedented amount of data since 2021 – over 1.4 billion vocalizations from more than 11,000 locations across the globe.

"Neil and I are determined to continue to apply the technology for wildlife conservation.”