In 2017, scientists watched the sky go dark during a Solar Eclipse, and across 17 species. Animals suddenly behaved differently, from giraffes running to tortoises mating, revealing a surprising response to the disappearance of daylight

When daylight disappeared over Columbia, South Carolina, on August 21, 2017, the change lasted only a few minutes. But inside a local zoo, the brief darkness produced striking reactions across a range of animals. Giraffes suddenly ran, Galápagos tortoises began mating, gibbons produced unusual vocalizations and gorillas started their bedtime routines. Researchers observing 17 species found that 13 changed their behavior during the eclipse. The surprising part was not simply that the animals reacted. It was how they interpreted the sudden disappearance of daylight.

The findings were published in March 2020 in the peer-reviewed journal Animals by Adam Hartstone-Rose, Edwin Dickinson, Lisa M. Paciulli, Kaitlyn Leonard and colleagues at North Carolina State University, together with Ashley Deutsch of the University of Florida, Leon Tran of the University of Hawaii and Grace Jones of the University of South Carolina. The study was titled “Total Eclipse of the Zoo: Animal Behavior during a Total Solar Eclipse.”

What did the animals do during the eclipse?

The total solar eclipse began at approximately 2:41 p.m. local time in Columbia, South Carolina, with near-total darkness lasting about two minutes and 36 seconds.

Researchers had already observed the animals during the days before the eclipse, giving them a baseline for how the species normally behaved during an August afternoon.

When totality arrived, the difference was striking. The Galápagos tortoises, which had been sitting in the sunlight, began mating. Siamang gibbons started producing extended vocalizations associated with unusual times of day, including sounds the researchers had not recorded from those individuals during their earlier observations.

The gorillas gathered together and began behaviors normally associated with settling down for the night. Hamadryas baboons ran and paced in groups while clustering around their young. Flamingos moved toward the center of their enclosure and vocalized, while rainbow and coconut lorikeets became louder.

Then there were the giraffes. The normally calm animals briefly began running. Lead author Dr. Adam Hartstone-Rose later explained that giraffes are “kind of delicate” and that when they run, it is generally because they are escaping a predator.

There was no predator during the eclipse. There was only an abrupt period of darkness in the middle of the afternoon.

Why did scientists expect something different?

Before the eclipse, the researchers had divided possible animal reactions into four categories. One category represented normal behavior. Another covered evening or nighttime behavior. A third was reserved for novel behavior, meaning actions that did not appear to correspond with the animals’ usual routines. The fourth covered apparent anxiety, including movements, vocalizations or clustering associated with fear.

The researchers had expected novel behavior to be prominent. A total solar eclipse is an extraordinarily unusual environmental event. Total eclipses over any particular location are separated by an average of roughly 375 years, meaning animals have not evolved with regular exposure to such an event.

The researchers therefore expected the animals might respond to the eclipse as something completely unfamiliar.

Instead, that was not the dominant response.

Of the 17 species observed, 13 changed their behaviour, or roughly 75 percent of the sample. The most common response was evening behaviour. Eight species displayed some form of their normal dusk or bedtime routine, even though the eclipse occurred roughly nine hours before the usual transition into night.

Novel behaviour was the least common category.

Were the animals responding to the eclipse itself?

The findings suggested that the animals were not responding because they understood that an eclipse was taking place.

Instead, they appeared to be reacting to the environmental signals produced by the event.

As the sunlight disappeared, the temperature dropped and the light faded. Those are cues animals can use to recognize the approach of dusk.

Inside the zoo, the surrounding environment was familiar and the animals were not facing an obvious external threat. Their response, in many cases, was therefore similar to what would normally happen when evening arrived.

The gorillas settled down. Other animals gathered together or produced vocalizations associated with later parts of the day. The Galápagos tortoises even began mating.

The behavior suggested that the animals were responding to the conditions around them rather than recognizing the astronomical event itself.

Did wild animals react in the same way?

Not necessarily. A separate study examined flying animals during the same 2017 solar eclipse. Published in Biology Letters in November 2018, the research was conducted by Cecilia Nilsson, Kyle G. Horton, Adriaan M. Dokter, Benjamin M. Van Doren and Andrew Farnsworth of the Cornell Lab of Ornithology and the University of Oxford.

The study, titled “Aeroecology of a solar eclipse,” used data from 143 weather radar stations across the United States, including eight located within the path of totality.

The researchers examined birds, bats and flying insects and found that daytime activity dropped sharply as totality approached.

But nighttime activity did not increase.

In other words, the flying animals did not appear to respond to the eclipse simply as though dusk had arrived. Instead, they largely stopped their daytime activity.

Cecilia Nilsson suggested that the combination of rapidly falling light and temperature may have resembled deteriorating weather to flying animals more than a normal transition into night. The Cornell Chronicle also reported on the study in November 2018.

Why did the same eclipse produce different reactions?

Taken together, the two studies point to an important difference between animals living in different environments. Inside the zoo, the sudden darkness could resemble an early evening signal. The animals were in familiar surroundings and had no immediate reason to flee.

For animals flying in the wild, however, the same environmental changes could signal something closer to bad weather. Their response was different because the surrounding circumstances were different.

The eclipse itself was therefore not necessarily the signal the animals were reacting to.

They were responding to the changes they could detect: fading light, falling temperatures and other environmental cues.

That helps explain why such different behaviors appeared during the same brief period.

The zoo animals did not need to understand what had caused the darkness. Their internal systems simply responded to the conditions around them.

The wild flying animals likewise did not need to identify the moon moving across the sun. Their behavior reflected the environmental signals those animals associate with changing conditions.

The 2017 eclipse therefore offered researchers an unusual opportunity to watch animals respond to an environmental change that arrived suddenly and disappeared just as quickly.

For many of the zoo animals, daylight vanishing in the middle of the afternoon looked enough like evening to trigger familiar routines. For flying animals in the wild, the same change appeared to produce a different response.

The result was a reminder that animal behaviour can depend not only on what happens in the environment, but also on how an animal's surroundings shape the meaning of those signals.

The animals were not watching the eclipse and reacting to it as an astronomical event. They were responding to what their senses were telling them was happening around them.

FAQs

How did animals react to the eclipse?
Many behaved as if evening had arrived.

Which animals behaved unusually?
Giraffes ran, while tortoises began mating.