Birds Went Silent during the Great North American Eclipse—Here’s What Researchers Discovered
When a total solar eclipse plunged North America into darkness on the afternoon of April 8, 2024, the songbirds of Bloomington, Indiana, suddenly fell silent. In the middle of the forest, the only sounds biologist Kimberly Rosvall could hear were the croaking of nocturnal frogs and the distant howl of a coyote. But when the sunlight returned after four minutes of “night,” so did the songs, as hundreds of birds greeted “morning” in unison with the joyous chorus of dawn.
“It was so amazing,” Rosvall says.
With his team at Indiana University in Bloomington, Rosvall worked with hundreds of people to gather information on how the solar eclipse changed the birds’ biorhythmic behavior. The results, published today in Sciencerepresent the largest effort ever to study such effects and provide important information for developing conservation strategies against ecological threats such as light pollution, the authors say.
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“Our research shows how sensitive organisms are to these changes in light in their natural environment,” says Rosvall. “Even a four-minute interruption is enough to reset their day. »
Few studies have analyzed in detail how certain bird species respond to solar eclipses, which occur when the moon is aligned so as to momentarily obscure the sun. Some sighting reports suggest that birds sing as if dawn has returned when sunlight returns, while others show an increase in bird sounds during darkness – a discrepancy that could be because some birds are more active at night and others more active during the day.
To help distinguish these species-based differences, Rosvall’s team created a smartphone app called SolarBird, and it was downloaded by volunteers along the eclipse’s path across North America, from Canada to Mexico. The app guided users to observe a bird for 30 seconds and tap icons describing its behavior, from singing to flying to feeding. Users did this three times: before, during and after the eclipse.
“Focal observation,” or observing an animal for a specific length of time, “is the gold standard for quantitative behavioral science,” says Rosvall. “It gives you an unbiased view of behavior.”
The team promoted the app to schools, local media and birding groups. But they were not prepared for what came next. In total, they received nearly 7,000 usable observations. “We were speechless,” Rosvall says.
To supplement the crowdsourced data, researchers deployed autonomous recording units at 14 sites around Bloomington. These microphones captured nearly 100,000 bird vocalizations before, during and after the eclipse. The sounds were then analyzed using BirdNET, an artificial intelligence platform developed by the Cornell Lab of Ornithology and Chemnitz University of Technology in Germany that can identify thousands of species from sound alone.
During the four minutes of totality of the eclipse – the period when the moon completely blocks the sun in the sky – bird vocalizations increased, while other activities such as flying, feeding and roosting decreased. After totality ended, many species changed their vocalization rates. In total, 29 of the 52 species analyzed via BirdNET showed changes in their song during at least one of three periods – before, during or after the eclipse – suggesting widespread but species-specific light sensitivity. Many species that naturally sing a chorus at dawn produced an increased number of vocalizations shortly after totality.
Some birds that sing most often when it is still dark, such as the American robin and the barred owl, showed an overall increase in the number of calls during the study. American robins, ubiquitous songbirds known for their loud predawn calls, experienced the largest increase in their vocalizations during the afternoon of the eclipse of any species studied: they increased their vocalizations more than fivefold. Barred Owls, usually active at night, were calling four times more than usual. Birds without a pronounced morning routine, such as house sparrows, showed little change.
The new study is an “incredible natural experiment” that provides a “rich and unique new data set” to challenge what scientists think they know about how birds of different species respond to drastic changes in light, said ornithologist Andrew Farnsworth of Cornell University. “There could be other types of behavior that are probably buried in their recordings that the authors are going to be able to analyze in more depth,” says Farnsworth, who was not involved in the new study. “There will be additional questions that need to be answered with their data.”
Rosvall’s first idea, for example, is that the 29 species showing drastic changes in their singing behavior should be flagged on a list of birds considered extremely sensitive to changes in light, she says. This could be useful for planning conservation strategies to limit light pollution, for example in and around natural bird habitats.
Only recently have scientists become more interested in studying the effects of eclipses on animals, says biologist Adam Hartstone-Rose of North Carolina State University. This is not for lack of curiosity, he adds, but because total solar eclipses are extremely rare events that almost never occur multiple times in the same location, complicating plans for in-depth studies of the site.
The next opportunities to conduct research of this type will arise in August 2026, when the total solar eclipse will plunge parts of Iceland and Spain into darkness, and in August 2027, when another eclipse will cover part of North Africa.
Rosvall’s study is an example of how these phenomena present an “incredible opportunity” to engage communities in the development of science, says Hartstone-Rose, who also studies how eclipses influence humans’ connection with the natural world.
In addition to being a rare phenomenon, the 2024 eclipse occurred during North America’s bird migration season, providing what could be a unique chance for professional and amateur scientists to perform an experiment of this type. “So many things lined up,” Rosvall says. “The next total solar eclipse in North America, at a particularly interesting time for birds, will be beyond my lifetime.”
