Solar eclipse reveals that darkness resets birds’ biological clocks

On April 8, 2024, day briefly turned into night. Across North America, birds stopped, sang, and stirred as the Moon’s shadow swept from Mazatlán to Newfoundland.

For four minutes and fifteen seconds over Bloomington, Indiana, darkness replaced daylight. This rare celestial event gave scientists a unique chance to study how sudden darkness affects wild birds.

Eclipse sparks unexpected bird songs

A team led by Ph.D. student Liz Aguilar in Kimberly Rosvall’s lab at Indiana University, seized the moment. Their study revealed that even a few minutes of darkness can disrupt the natural rhythms that guide bird behavior.

Researchers from the Luddy School of Informatics, Computing, and Engineering joined forces to explore these fleeting shifts using both artificial intelligence and citizen science.

When night arrived unexpectedly, many birds sang as though it were dawn. This “false dawn chorus” showed how deeply birds rely on light to regulate their behavior.

The eclipse caused more than half of the observed species to alter their activity patterns, from vocal bursts to sudden silences.

Community and science unite

The project began when Jo Anne Tracy, assistant dean for research and director for Science Outreach, gathered educators to plan public engagement for the eclipse.

That meeting linked Aguilar with Paul Macklin, a professor at the Luddy School. Together, they envisioned a project that would merge public enthusiasm with rigorous science.

The team’s vision became SolarBird, a smartphone app built to involve people in real-time data collection.

“Scientists can’t be in a thousand places at once,” Aguilar said. “The app gets around this problem by leveraging the public as scientists.”

Participants observed birds for 30 seconds before, during, and after totality, documenting actions like singing, flying, or eating. The app recorded GPS coordinates and calculated how much of the Sun was covered by the Moon.

“A main theme was how we could make data collection easy for newcomers, and minimize any distractions from the day’s event,” Macklin said.

Birds recorded by thousands of people

SolarBird generated nearly 11,000 observations from over 1,700 users across the continent. “It was important to us to publish their names in our paper,” Aguilar said.

“The app worked. And as we looked at the database that night, we saw the community had also worked its magic,” Macklin said.

Meanwhile, Rosvall’s team used autonomous recorders around Bloomington to capture the soundscape before, during, and after the eclipse.

Dustin Reichard, now at Ohio Wesleyan University, helped deploy these recorders and analyze nearly 100,000 bird vocalizations using the AI system BirdNET.

Eclipse darkness changes birds’ voices

The recordings revealed dramatic behavioral shifts. During the eclipse, 12 bird species changed their singing patterns, with some going quiet while others grew more active.

After totality, 19 species increased their vocalization rates, mirroring a dawn chorus. Robins sang six times more often, while barred owls called four times as frequently as usual.

According to the new analysis, birds that usually sing at dawn were most likely to react. Researchers found that even four minutes of darkness could reset biological rhythms.

Aguilar’s team discovered that dawn singers began new morning songs as soon as sunlight returned, showing how precisely birds respond to light cues.

A false night, real effects

The study’s theoretical foundation connects to circadian biology. Birds, like most organisms, use light-dark cycles to synchronize their daily and seasonal activities. The sudden interruption of light during an eclipse acted as a massive natural experiment in resetting these bird internal clocks.

The researchers compared this to the opposite effect of artificial light at night, which disrupts biological rhythms and affects ecosystems worldwide.

The experiment demonstrated that light, not just time, drives behavioral rhythms. Even a brief “false night” was enough to trigger large-scale changes across species.

The team emphasized that such responses show how sensitive animals are to rapid light variation, independent of other factors like temperature or weather.

Linking AI and solar eclipse

Rosvall’s team noted that this study was distinct from traditional lab research. Unlike artificial experiments using constant light or darkness, the eclipse offered a real-world, large-scale test free from human manipulation.

By pairing AI-based analysis with citizen science, they revealed how the return of light acts as one of the most powerful cues in nature.

“You can turn off the Sun, even briefly, and birds’ physiology is so tuned to those changes that they act like it’s morning,” Rosvall said.

The findings hold broader relevance, offering clues about how urbanization and artificial lighting reshape ecosystems and animal behavior.

Shared wonder, shared knowledge

Rosvall believes this combination of technology and community involvement marks a shift in modern ecology.

“It was clear that engaging in this research project enhanced people’s joy in this experience,” she said. “It did for me and those who reached out.”

For Aguilar, it remains her proudest project. “It shows that sometimes a creative idea and a willingness to go all in is what you need to accomplish high-impact work,” Rosvall said.

The study received support from the Indiana Space Grant Consortium and the National Science Foundation.

By combining artificial intelligence, public participation, and an event that occurs once in centuries, this research proved that when the Sun disappears, science shines brightest.

The study is published in the journal Science.

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