When the Moon Obscures the Sun, How Does Life on Earth Respond?

From fish to flamingos, here’s what scientists know — and what they hope to find out — about how plants and animals react to a total solar eclipse

People have long been fascinated with how solar eclipses affect life on earth. This image of an eclipse in 1846 was included in the Annual Report of the Smithsonian’s Board of Regents of that same year. Smithsonian Libraries

If the sky briefly went dark during the middle of the day in ancient Greece, people took this to mean that the gods must be angry. Around the world and throughout history, an unexpected dark sky brought fear, amazement, and wonder. People have come up with countless variations to explain this puzzling phenomenon: the sun must be furious, or the sun is sick, or the sun has dropped its torch.

Now, humans know that a sudden darkening of the sky can be due to a meteorological event called a solar eclipse, which occurs when the moon passes between the Earth and the Sun.

On April 8, 2024, large swaths of North America will experience a total solar eclipse, during which the sun’s light will be completely blocked from certain perspectives on Earth for about three to four minutes. During this temporary outage of solar light, people will gather to watch the sky, don “eclipse glasses” to protect their eyes and uncover long-abandoned digital cameras.

But humans won’t be the only species in the eclipse’s path to respond in unusual ways. Here’s what we know so far about how animals will react to a total eclipse, and what questions scientists are hoping to answer during the April 8 event.

Swapped Sleep Schedules
During a solar eclipse, some spiders begin to deconstruct their webs. Feininger and Andreas, Smithsonian Institution

Humans have a sleep cycle — or circadian rhythm — that is largely internal. Anyone who has experienced jet lag is familiar with the frustrating feeling of one’s body being out of calibration with the local time.

But for some organisms, waking and sleeping cycles are almost entirely dependent on the sun. This means that the darkness caused by an eclipse can trigger the responses that are typical of night.

Fish, for instance, respond to decreased light intensity during a solar eclipse the way they would respond to dusk. During a 1998 total eclipse in the Galapagos, diurnal fish rapidly adopted nighttime behavior, while nocturnal fish gradually left the cover of their daytime habitats. Similarly, foraging bees ceased flying during the totality of the 2017 eclipse, instead returning to their hives. Spiders that typically took down their webs at dusk began dismantling them during a total eclipse in 1991.

Large mammals also took a bedtime cue from the eclipse. A pair of African elephants approached the entrance of their barn during totality at the Riverbanks Zoo in Columbia, South Carolina, in 2017, as if they were headed to sleep. This zoo also had a group of gorillas enter their enclosures during the dark spell as they did every evening.

Chaos and Commotion
This photograph from 1910 shows European flamingos at the National Zoological Park. During a solar eclipse, flamingos flock together and show apparent anxiety. Smithsonian Institution

Unlike the creatures that simply start their nighttime routine early, some species have a frenzied response to the eclipse. Flamingos, for instance, exhibited restlessness and anxiety during the 2017 totality. The birds flocked together and vocalized loudly, and in some cases paced around their enclosure and swarmed together at the onset of the eclipse at both the Riverbanks Zoo and the Nashville Zoo.

Giraffes also moved more during the unusual darkness. Some giraffes even began to gallop for several minutes during totality and pace around their enclosure following the event. Meanwhile, a pair of tortoises at the Riverbanks Zoo began mating just before the eclipse, while other tortoises became more active and moved rapidly. After the eclipse, the tortoises gazed up at the sky.

Researchers at zoos across the path of this month’s total solar eclipse are planning to study animal behavior during totality. This will include zoos everywhere from Fort Worth, Texas, to Indianapolis, Indiana.

Paused Productivity
This photo of sagebrush in the Columbia river basin was taken in 1909. During a solar eclipse, sagebrush is not able to photosynthesize as much as usual. Asahel Curtis, Wikimedia Commons

Though there may be less vocalizing and movement amongst plants than members of the animal kingdom, the effect of a solar eclipse on these organisms is still profound. With lower temperatures, lower vapor pressures and less light available during a solar eclipse, plants have a limited ability to photosynthesize during the eclipse.

One study from the 2017 eclipse estimated a 14% reduction in photosynthesis over the whole day in a sagebrush area in the Western U.S. According to the study’s authors, this can be especially harmful if the plant is already experiencing drought conditions. Another study conducted during a total solar eclipse in Chile found that shade-intolerant trees were more susceptible to a solar eclipse than shade-tolerant trees were.

Mangled Migrations
Bird migration may be affected by a solar eclipse, as new studies on April 8 will test. Wikimedia Commons

For many organisms, the sun is not only a cue for when to go to sleep, but also when to migrate. Solar eclipses have been shown to impact the mass movement of organisms from one location to another.

The world’s largest migration event is the daily upwelling of zooplankton in the world’s oceans  from the depths to shallower water in response to signals from the sun. This daily movement, called Diel Vertical Migration or DVM, occurs at sunrise and sunset. During the 2017 eclipse, scientists found that this mass migration event occurred during the eclipse as it would at dusk off the coast of Oregon. The zooplankton migrated up as the sky darkened then returned to the deep ocean as the sun reappeared from behind the moon.

Bird migration may also be impacted by decreased light levels during the solar eclipse. Some birds are diurnal migrants that travel mainly during the day, while others are nocturnal migrants that prefer to migrate at night. In a 2017 paper on migration during a solar eclipse, researchers found that the total eclipse provided a cue for diurnal migrants to cease flying but did not cause nocturnal migrants to start flying.

The Cornell Lab of Ornithology and the NASA Eclipse Soundscapes Project both plan to further investigate migratory behavior during the eclipse. Because this month’s eclipse takes place during the spring migration season, it will be an opportune time to research how migratory birds respond to a total solar eclipse.

Unbothered and Unfazed
A group of people observe a solar eclipse in Kawar, India in 1980 with a team of Canadian and US scientists. François LOCHON/Gamma-Rapho via Getty Images

There is also a category of organisms that do not let solar eclipses throw off their typical routines. Household pets like cats and dogs tend to be unfazed by an eclipse. Domesticated farm animals like dairy cattle also show little responce to a solar eclipse. And even our closest relatives, chimpanzees, react only by looking up at the sky.

Although humans understand what an eclipse is and how best to react (don’t look at the sun without safety glasses!), we still know very little about how plants and animals on earth will react. With several intriguing scientific studies slated for April 8, we may get a better understanding than ever of how a solar eclipse affects sleep, anxiety, migration and other behaviors throughout the animal kingdom. 

Related Stories
A Brief History of Eclipse Chasers
Five Fascinating Science Projects Using the Total Solar Eclipse to Illuminate New Discoveries
Turning Off Your Lights Could Save Millions of Birds Each Year from Deadly Building Collisions
Peer Through the Glare to Glimpse the Night Sky in New Smithsonian Exhibition
What Does an Eclipse Sound Like?