Biologist Adam Hartstone-Rose had one big question on his mind heading into this month's solar eclipse: Why are animals so stressed out during totality?
On April 8, as the moon crossed in front of the afternoon sun and plunged the area into sudden darkness, he and a team of researchers, zookeepers and high school students observed nearly three dozen different species at the Fort Worth Zoo in Texas. Hartstone-Rose says the animals were considerably less stressed than those he observed during a solar eclipse seven years ago — and thanks to "groundbreaking" preliminary data, he has an explanation.
'Quite dramatic behavior'
In 2017, Hartstone-Rose, a biology professor at North Carolina State University, organized a study of animal behavior during the total solar eclipse at Riverbanks Zoo & Garden in Columbia, South Carolina. He says he was not enthusiastic about eclipses until he discovered how little researchers knew about animal behavior during them. Scientists had not attempted a study of this scale since 1932.
Hartstone-Rose says his team observed "quite dramatic behavior" during totality in 2017. Giraffes stampeded. Galapagos tortoises began mating. Gibbons made an unusual calling sound. What intrigued him most was not the eccentric behaviors themselves, but why they were occurring.
"A huge number of animals actually responded as if they became really upset and stressed out. And we weren't sure why they behaved that way," he says.
That observation guided this month's study, which involved an array of species including bonobos, owls, coyotes and crocodiles. Hartstone-Rose says the data illuminated a nearly universal reaction across species — one that the team had noticed in 2017, but were able to confirm earlier this month: At the moment of totality, when the sky grew dark, animals began their regular evening routines as if nightfall had officially arrived. For nocturnal animals, this meant heightened activity. For diurnal animals, it meant napping, heading indoors or anticipating dinner.
Hartstone-Rose says the most extreme reaction his team witnessed earlier this month was from Aldabra giant tortoises.
"These giant tortoises that each weigh over 100 pounds wanted to get into their evening barn so badly that they reared up on their hind legs, which I didn't even know tortoises can do, and they pushed so hard against the door that they actually bent the door frame," he says.
Pierre Chastenay, a Canadian astronomer who helped lead a separate study of 12 species at Zoo de Granby in Quebec, Canada, echoed these findings. He was tasked with observing Japanese macaques, and recalled that at the moment of totality, they bowed their heads and prepared to go to sleep. A few minutes later, they became active again, and began foraging for food, grooming and chatting.
"They were talking to one another in their macaque language, probably saying something like, 'What the hell just happened? This is the shortest night I've ever had,'" Chastenay says.
Accounting for the human factor
Hartstone-Rose says animals experience a low degree of stress when their evening routine is disrupted, "like turning the stress dial up to a level one or two." On April 8, the species Hartstone-Rose and Chastenay separately observed never became stressed or erratic beyond that low level — unlike in 2017. The two researchers connected in the weeks leading up to the eclipse, having heard they were pursuing similar studies. As for why stress remained so low, they have a hypothesis: fewer screaming people.
"This is seemingly really strong evidence that animals that exhibit anxiety during an eclipse are anxious not because of the eclipse itself, but because of the human reaction to the eclipse," Hartstone-Rose says. "We think that the animals are just much more perceptive of our own emotionality during an eclipse than we previously sort of gave them credit for."
Hartstone-Rose recalls fireworks, cheering, and chaos where he was stationed along the path of totality in 2017. In contrast, during this month's solar eclipse, the Fort Worth Zoo had chosen to limit crowds for its watch party. They capped the event at roughly 2,200 people, which was modest compared to a typical weekend capacity of 8,000.
At Zoo de Granby, there were no cheers from visitors at all. The zoo was closed to the public that day, which is typical of weekdays in the off-season. Chastenay says during totality, the animals engaged in normal, instinctive evening behaviors with little interruption. Nocturnal animals were active, and diurnal animals were calm.
"I think that our study will be a landmark, so to speak, because from now on, if people want to conduct this kind of study in zoos during a total eclipse, they will have to take into account the presence or not of humans going crazy during totality," Chastenay says.
Hartstone-Rose says despite the findings of his study, he does not believe zoos need to restrict or eliminate visitors during future eclipses. Instead, he says, zoos are "a magical place to be" during such events, and the cost of momentary stress for animals is low.
"Zoo animals actually have it pretty good compared to their wild brethren," he says. "We should be aware of trying to reduce the stress in zoo animals, especially if they are habitually stressed. But allowing animals to become stressed on occasion is actually a very natural state for them."
Both scientists are looking ahead to future eclipse events. Hartstone-Rose hopes to translate research tools into other languages in order to determine if researchers on other continents observe similar animal behaviors. He also plans to survey animals in their wild environments, including during a total solar eclipse that will cross southern Africa in 2030.
"I think this is the beginning of a very fruitful collaboration," Chastenay says of his work with Hartstone-Rose.
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