Artificial light is extending the waking hours of birds around the world changing not just their daily routines, but potentially their long-term health and behavior. A groundbreaking global study now confirms that light pollution is significantly altering avian activity, with birds in the brightest areas singing nearly an hour longer than those in natural darkness.

Cities That Never Sleep Disrupt Natural Rhythms

Streetlights, billboards, and urban glow have made darkness a rarity in many cities. While this benefits human convenience and commerce, the growing brightness has unintended consequences for wildlife. Birds, in particular, are highly sensitive to light cues that regulate their daily behaviors—including singing, foraging, and rest.

A new study led by Brent Pease of Southern Illinois University and Neil Gilbert of Oklahoma State University reveals how widespread artificial lighting is lengthening the active hours of birds across the globe. Their findings are based on an analysis of more than 180 million bird vocalizations paired with satellite imagery of nighttime light exposure.

Birdsong Extended by Nearly One Hour

“We were shocked by our findings: Under the brightest night skies, a bird’s day is extended by nearly an hour,” said Pease.

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Birds exposed to high levels of artificial night light began singing earlier in the morning and continued later into the evening, significantly stretching their typical daily vocal activity.

But not all species responded the same way.

Eye Size Matters: Some Birds Are More Affected Than Others

To understand what makes some birds more sensitive to light pollution than others, the researchers explored a novel hypothesis: eye size.

Their analysis found that species with larger eyes relative to body size showed stronger responses to artificial light at night, likely due to their greater light sensitivity. These birds were more likely to remain active after dark, compared to species with smaller eyes.

The implications are significant species-specific vulnerabilities mean that light pollution could reshape ecosystems by affecting predator-prey interactions, breeding patterns, and competition for resources.

Noisy Nights: Sound Pollution Adds Complexity

The study also explored the influence of noise pollution, often a byproduct of urban light. Birds living near roads or highways behaved differently than those in quieter settings, suggesting that noise may play a secondary role in shaping avian behavior. However, the most consistent behavioral changes were tied to light, not sound.

Interestingly, nocturnal birds responded in the opposite way. In brightly lit environments, they became less vocal and shortened their nighttime activity, reducing their calls by up to 30%. The presence of moonlight also impacted behavior, with bird activity rising or falling depending on lunar phase.

A Classroom Project Turned Global Breakthrough

Pease originally launched the project as a creative undergraduate initiative, installing a microphone at Touch of Nature Outdoor Education Center and streaming live birdsong into the university's agriculture building. This classroom tool quickly evolved into a global conservation study.

By using BirdWeather devices and data from BirdNET, a machine learning platform co-developed by the Cornell Lab of Ornithology, the team was able to track avian behavior 24/7 across thousands of locations and over 6,000 bird species. Spectrograms helped identify and compare vocalizations at scale, unlocking new insights into behavioral shifts.

BirdNET and Citizen Science: A New Era for Conservation

“This is citizen science at its best,” Pease said. “A tool designed for people to track birds in their own backyards has collected over 1.4 billion bird vocalizations from more than 11,000 global locations since 2021.”

Thanks to machine learning and public participation, the project is ushering in what Pease calls a “golden age of avian conservation.”

The implications are vast not only can researchers study where birds are, but also how they behave across seasons, geographies, and environmental changes.

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What’s Next: More Research, More Responsibility

Whether longer activity windows benefit or harm birds remains unclear. On one hand, more singing time could help birds attract mates or find food. On the other, less rest could increase stress, reduce fitness, and disrupt breeding cycles.

Pease and Gilbert plan to continue their work, using the vast BirdWeather dataset to study how climate change, urbanization, and other stressors are reshaping bird life globally.

In the meantime, their research sends a clear signal: Light pollution is not just a human issue. It’s a global ecological force—one that’s reshaping life song by song, hour by hour.

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