Birds, bees and even plants might act weird during the solar eclipse

A total eclipse isn’t just a spectacle in the sky. When the moon consumes the sun on April 8, day will plunge into twilight, the temperature will drop — and nature will take notice.

Reports abound of unusual animal and plant behavior during eclipses. A swarm of ants carrying food froze until the sun reemerged during an 1851 eclipse in Sweden. A pantry in Massachusetts was “greatly infested” with cockroaches just after totality in 1932. Sap flowed more slowly in a 75-year-old beech tree in Belgium in 1999. Orb-weaving spiders started tearing down their webs and North American side-blotched lizards closed their eyes during an eclipse in Mexico in 1991.

Plenty of scientists see eclipses as rare opportunities to bolster anecdotal reports by studying how nature responds — or doesn’t — to a few minutes of dusk in the middle of the day. That’s why teams across the country produced a swarm of studies about plant and animal behavior during the last total eclipse to cut across the United States in 2017.

Some of these scientists found that when the sun vanished, insects, birds and plants seemed to enter into something approaching a nocturnal pattern. Case in point: Scientists in multiple states reported that fireflies started flashing, and a team in Idaho captured two species of voles that are normally active at night.

Bat researchers in Georgia, on the other hand, weren’t convinced that the eclipse had any effect on behavior, though they noticed slightly more bat activity on the night after the eclipse than on previous or subsequent nights. Beetles flew around as normal in South Carolina.

Understanding how eclipses affect nature writ large is nearly impossible. That’s because eclipses don’t follow one of the most basic rules of science: replication. They don’t happen with regularity in the same spot. They vary in length. They happen at different times of day, during different seasons.

“A lot of the things we found in the literature were exactly that — a curiosity. It happens once every so often, so it’s curious, but not generally informative of animal behavior,” said Olav Rueppell, a scientist who studies honeybee biology at the University of Alberta in Canada.

And while an eclipse is an incredible time to observe the natural world, there’s also a potential observer effect: People who might normally be at school, at work or simply distracted are looking and listening closely, and what they see as responses to the eclipse could just be normal behaviors that escape notice on a typical day.

Adam Hartstone-Rose, a professor of biological sciences at North Carolina State University, led a study of how animals reacted to the 2017 eclipse at the Riverbanks Zoo in Columbia, S.C.

“At any given point on Earth, a total eclipse occurs once every 375 years. So it’s not like you’re learning something now you can use again in the future, and that’s certainly true for animals,” Hartstone-Rose said.

“But it’s a unifying event. All of us have this experience together,” he said, adding that during the April eclipse, “we’re all going to be communing with animals and thinking about how they experience it.”

Studies of animal behavior during an eclipse tend to fall into two categories. Some biologists who are near the path of totality will design a study to see how the eclipse affects their favorite organism, whether it be honeybees or chimpanzees. Others try to activate members of the public to take data and make observations all across the path, which the scientists can use to discern broad patterns.

The NASA-backed Eclipse Soundscapes project, for example, will collect audio data and observations from hundreds of people during the April eclipse to repeat, with a bit more rigor, a citizen-science study of animal responses to a 1932 eclipse.

In his team’s 2017 study of zoo animals, Hartstone-Rose had researchers systematically observe 17 species, including baboons, flamingos and Galapagos tortoises.

Most responded to the eerie darkness in some way — whether by starting their bedtime routines, acting anxious or mating. Giraffes that had been munching on lettuce and chewing their cud huddled near their barn or galloped through their exhibit. A Komodo dragon that hadn’t moved in a day raced around its enclosure and climbed up the wall.

Hartstone-Rose is repeating the observations this year at the Fort Worth Zoo in Texas, and he is drafting more than a thousand volunteers across the country to collect records of animal behavior through a project called Solar Eclipse Safari. He’s as interested in the anomalous behavior of animals as he is in learning how observing animals and trying to understand their experience affects humans, perhaps widening their sense of wonder and awe.

One common report is that birds go to roost and go quiet during an eclipse. But when a team of ornithologists from Cornell University made recordings along an old logging road near the town of Corinna, Maine, for the 1963 eclipse, they heard the per-chic-o-ree of a goldfinch in the middle of totality, along with a hermit thrush, a Swainson’s thrush and a veery.

“Perhaps no two lists of birds heard before, during, and after the eclipse would be anywhere near similar,” they wrote in their summary of the observations.

In the 50 minutes before and after totality in 2017, researchers monitoring flying insects and birds via the weather radar network found that the skies went eerily quiet, but there was an intriguing uptick of activity right at totality. The researchers speculated that it might be some kind of insect reacting to the sudden darkness, while the birds possibly grew still due to confusion.

“Some previous research shows that insects react much more immediately to light cues, while birds are more like, ‘What’s going on?’” said Cecilia Nilsson, a biologist at Lund University in Sweden. “Totality only lasts a few minutes, so by the time you’re figuring it out, it’s over.”

For bird lovers, the many uncontrollable variables of an eclipse can be scientific opportunities, too.

One exciting aspect of the 2024 eclipse is that it is happening during the spring, whereas the North American eclipse of 2017 took place very early in the fall migration season, Nilsson said. Many birds, she noted, migrate at night and are often more motivated during the spring migration, so it’s possible that abrupt darkness will have a different effect this time around.

Rueppell, the honeybee scientist, was based in North Carolina during the total eclipse in 2017. He decided with collaborators to try to bring some rigor to previous observations of honeybee behavior.

A crowdsourced compilation of observations from a 1932 total eclipse, for example, included reports of a swarm of 200 bees showing “apprehensiveness” in the minutes before totality. Another observer reported that “as darkness increased the outgoing bees diminished in numbers and the return battalions grew larger.”

Rueppell and colleagues at Clemson University in South Carolina enlisted observers to watch the entrances of hives, counting how many honeybees were exiting and how many were returning from foraging trips before, during and after totality. They made some hives hungrier than others by taking the bees’ honey away before the eclipse, to see if that changed their willingness to forage.

The researchers found that the environmental cues overrode bees’ own internal circadian clocks, with darkness causing them to return to the hive and hunker down. Those findings square with another study that found bees stopped buzzing around flowers during totality. But hives that were stressed by hunger shut down less completely than those that weren’t.

They also conducted a second experiment, putting fluorescent powder on bees and releasing them away from their hives, then measuring how quickly they returned.

Right before totality, they found the bees were returning faster, almost as if they were panicked.

Daniel Beverly, a plant ecophysiologist at Indiana University, studied how sagebrush in Wyoming reacted during the 2017 eclipse. A total eclipse last passed over Wyoming in 1918, though it traversed different parts of the state.

“These plants are 60 to 100 years old, and they’ve never seen this midday darkness,” he said. The scientists found that photosynthesis plummeted during totality, then took hours to recover from the shock of the sun reemerging minutes later.

This year Beverly will be measuring ecological responses to the eclipse at a forest in Indiana that is part of a long-term project monitoring carbon, water and energy flux through the ecosystem. Because the Morgan-Monroe State Forest is already the subject of intense scientific scrutiny, scientists can take advantage of existing instruments to measure factors such as carbon flux and water movement in white oak, tulip poplars, sassafras and sugar maples.

Beverly noted that he’s excited to get as much of the data collection automated as possible so he and his team can fully appreciate the brief but wondrous moment of totality.

“It is pretty awesome and life-changing,” Beverly said. “Just the spectacle of it. I don’t know what it does to the human brain.”