How Animals and Nature React to an Eclipse

March 25, 2024 10:07 AM EDT

Of all of the animals worth observing during a total solar eclipse, some of the most intriguing are humans. They stop what they’re doing; they stare skyward; they lower their voices to a hush. Some may gather their young close. Some may even shed tears. If you’ve ever witnessed a solar eclipse yourself, none of this comes as a surprise; indeed, you’ve surely exhibited some of these behaviors too. Other species of animals display other kinds of behavioral changes, as the weather and lighting and nature itself seem to turn on their axes. So what should you expect to experience on April 8, as a total eclipse crosses the U.S. from the southwestern edge of Texas to the northern tip of New England?

Some of the greatest changes will occur far above us, in the ionosphere, the band of atmosphere that ranges from an altitude of 60 to 300 km (37 to 190 mi.). Defined by the abundant presence of electrically charged particles, or ions, the ionosphere is denser during the day, turbocharged by incoming radiation from the sun.

As NASA explains, that means that during an eclipse, the overall concentration of ions in the ionosphere falls. This reduction can lead to a cooling of the upper atmosphere, which in turn can cause local depletions known as “ionospheric holes.” That has an impact on populations on the ground as those cavities may disrupt the transmission of radio signals and lead to anomalies in GPS navigation systems. As researchers at Embry-Riddle University and Clemson University determined after the 2017 total eclipse, however, in most cases the GPS disruption is transitory and too mild for users to notice.

Other natural changes are more universally detectable, not least the steady dimming of sunlight. The arc of totality across North America measures just 185-km (115 mi.) wide. In this band, a sort of deep dusk descends, with a much subtler darkening the farther you move from that central point. In 2017, a team from TIME traveled to Casper, Wyo. to record and report that year’s eclipse from a hillside overlooking the bowl of the city. Streetlights and headlights flicked on as the sunlight rapidly retreated.

If you’re outside during totality, it may pay to have a sweater or a jacket with you. Temperatures can drop by anywhere from 2.8°C to 8.4°C (5°F to 15° F) as the sunlight retreats, according to the Weather Channel. Falling temperatures near the earth’s surface also may cause what’s known as an “eclipse wind,” or a slowing of the winds. That’s the result of low-level air becoming cooler than the higher level air above it—what’s known as a temperature inversion—which makes it harder for that more-elevated atmosphere to mix with the air closer to the ground, eliminating the temperature and density differences that lead to breezes and gusts. As totality ends, the winds pick back up.

Another effect falling temperatures may have will be the appearance of a fleeting thunderstorm, as cooler air closer to the ground pushes warmer more humid air upward, where moisture then condenses and rains out. The process is similar to the way ocean breezes can cause brief storms in the summer.

All of this affects non-human animals in multiple ways. Insects, bats, and birds that feed at night emerge as the sky darkens, sometimes in sufficient numbers to be detectable on radar, says the Weather Channel. Birdsong tends to grow quieter as darkness descends, rising back up as the light reappears. Crows, gulls, and sparrows that are in flight have been observed alighting on trees or on the ground and silencing any chirps, calls, or caws. Dogs may cower or exhibit other fearful behavior. Bees may return to their hives and domestic horses and cows may move to their stables, reports Liz Aguilar, a PhD candidate in biology in the University of Indiana's evolution, ecology, and behavior program. In wild herds or in distant paddocks away from their barns, horses may also cluster and begin shaking their heads and tails—though it’s not entirely clear why they engage in these movements. Head-shaking and tail-swishing are far more common as an agitated response to flies, or to resistance to or discomfort from being ridden. So-called “photic head-shaking” actually occurs when horses are exposed to bright sunlight—precisely the opposite to what happens during an eclipse.

In a 2020 paper in the journal Animals, researchers observed both domesticated and zoo animals and recorded a range of eclipse-related behaviors. The cowering and other expressions of anxiety seen in dogs were also observed in baboons, gorillas, giraffes, and flamingos, as well as in parrots and other species of lorikeets. Tortoises, Komodo dragons, and other forms of reptiles, which already may be lying largely unmoving in the sun, grow more stationary still.

Perhaps most striking though, was the behavior of a captive troop of chimpanzees at the Yerkes Primate Research Center on the campus of Emory University in Georgia, during an annular eclipse on May 30, 1984. As researchers reported in the American Journal of Primatology, the animals moved to the highest point of a climbing structure in their enclosure and turned their faces upward in the direction of the sun and the moon. One juvenile gestured toward the slowly vanishing sun. The chimps remained that way until the skies began to brighten, when they descended from the structure. No one can ever say with certainty how they were experiencing what they were seeing—whether they felt their own form of curiosity or wonder or even reverence. Clearly, though, they were captivated by it all. It is a reaction that is very much of a piece with what humans feel—one we may share with untold numbers of other species as the great solar sky show unfolds.

More Must-Reads from TIME