For a few precious minutes on August 21, darkness will descend across the United States as a historic total solar eclipse crosses the continent from coast to coast.
Millions of people already live under the path of totality, and tens of millions more will make the trek to see the moon blot out the sun. Astronomers already expect that this eclipse will be the most witnessed sky-watching event in human history. (See our map of the best places to watch the solar eclipse.)
But according to biologists and long-time eclipse chasers, humans won’t be the only ones reacting to the dramatic changes in the sky.
During a total eclipse, the sky darkens to twilight levels and air temperatures drop. Over the centuries, people who have witnessed these effects have also noted that a variety of animals seem to change their behaviours in response.
Learn more about how solar eclipses happen, the four types of eclipses, and how to view the sun safely if you're within the path of totality.
DAY TURNS TO NIGHT
Reports of unusual animal reactions to solar eclipses date back centuries. One of the earliest stories comes from Italian monk Ristoro d'Arezzo, who described what happened during a total eclipse on June 3, 1239.
As the sun disappeared and the sky turned dark, “all the animals and birds were terrified; and the wild beasts could easily be caught,” he wrote.
During an eclipse seen in Portugal on August 21, 1560, astronomer Christoph Clavius wrote that during totality, “stars appeared in the sky and (marvellous to behold) the birds fell down from the sky to the ground in terror of such horrid darkness.”
While it’s hard to confirm such colourful anecdotes from history, modern astronomers and eclipse chasers have also reported wild and domestic animals noticeably reacting to eclipses: Dairy cows return to the barn, crickets begin chirping, birds either go to roost or become more active, and whales breach in the seas. (Take our solar eclipse quiz.)
Veteran eclipse-chaser Peter den Hartog travelled to Hungary in 1999 to experience totality, and he remembers seeing various species of birds and bats suddenly appear during totality.
“[Was it because of] the light intensity, or the flies and mosquitoes that came out … I'm not sure, but I‘ve definitely experienced more activity during eclipses,” Hartog says.
Eclipse-chaser and author Dave Balch was in Kona, Hawaii, for the 1991 total eclipse and noticed excited activity among the birds along the pier during the partial phases before and after totality.
“We could hardly hear each other talk! Then came totality – not a sound. It was deathly quiet. The difference between the noise levels before and during totality was stunning.”
And eclipse-chaser Tora Greve was on an expedition to Zambia in 2001 when she noticed that, just as the sun disappeared, frogs began making sounds and raptors stopped circling, possibly due to the change in thermals as the air cooled.
Around the water hole where she was standing, she says, giraffes “started running about during the whole totality. When the sun came back, they stopped and began grazing the trees again.”
However, collecting scientifically meaningful data on animal reactions to total solar eclipses is tough business. The paths of eclipses are scattered around the world, and many are visible only from remote regions. That makes it hard to obtain anything more than a few data points per event.
“If you really want to study behaviour in a comprehensive way, you have to spend a lot of time in the field observing and have rigorous protocols in place,” says ecologist Rebecca Johnson at the California Academy of Sciences.
“If you are an animal behaviour ecologist setting up to just study effects of solar eclipses, it can be near impossible.”
To improve the scientific record, Johnson helped create the Life Responds project, which runs on a dedicated smartphone app called iNaturalist. Her team of biologists and astronomers will use the app to collect data from the millions of people who will witness the eclipse on August 21.
“We created this project that very simply asks people wherever they are—whether they are under totality or partial eclipse—to spend some time outside looking at animals and observing their behaviour before, during, and after the eclipse,” she says.
Watch for orb-weaving spiders to destroy their webs during an eclipse.
PHOTOGRAPH BY ALEX SABERI, NATIONAL GEOGRAPHIC CREATIVE
The Life Responds team recommends that people who want to take part scout out in advance where they will be watching the eclipse and think about which animals will be around them. For instance, if you happen to be in a suburban backyard or city park, you may be best able to report on urban invertebrates such as ants and spiders.
Anecdotal evidence suggests that orb-weaving spiders destroy their webs during an eclipse, so Johnson recommends finding a web to watch.
“That might be something particularly easy for people to observe,” she says, “because [spiders] don’t move very far like flying birds, and so there is a higher likelihood of recording slower invertebrate behaviour.”
The hope is that the Life Responds app will create a meaningful clearinghouse for animal behaviour during eclipses that scientists can use to advance their research.
“The collection of observations and looking for patterns is where science begins, and we hope to bring scientists to the data to spur their research moving forward,” Johnson says.
“Hopefully we’ll end up documenting something that no one has ever seen before.”