Something weird is happening to these Alpine goats. Scientists say it’s an ominous sign.

Climate change and other human impacts are turning some animals nocturnal.

A day in the life of a goat in the Alps is, perhaps, as idyllic as it sounds. Wake up when the sun rises. Eat some grass and wildflowers. Rest. Go to sleep when the sun sets, high up on the mountain, among protective rocks.

For thousands of years, this has more or less been the life of Alpine ibexes, a type of mountain goat in the European Alps with almost comically large horns.

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But life for these goats — however quaint it once was — is rapidly changing. As our cars and factories continue warming the Earth with a blanket of greenhouse gases, Alpine ibexes are becoming increasingly nocturnal, new research in the Proceedings of the Royal Society B has found. Following exceptionally hot weather, these goats switch up their routine and spend more time foraging at night, according to the study, led by the University of Sassari and the University of Ferrara in Italy.

“Ibex cope with warmer temperatures by becoming more nocturnal,” the authors wrote. (The Alps are expected to be several degrees hotter, on average, by the end of the century, compared to the late 20th century.)

By turning into a night owl (or, night goat), these animals are, in a sense, adapting to life on a warmer planet. But such changes likely come with troubling consequences. For one, wolves — the main predator of ibexes in this region, the authors say — typically hunt under the cover of darkness. Plus, these goats don’t see well in the dark and live in highly treacherous terrain.

This research is just one example of how humans are altering the daily lives of animals, often making them more nocturnal as a result. A 2018 study, led by the University of California Berkeley, found that a range of human activities, such as hiking or hunting, is causing mammals of all kinds to be more active at night, from the US and South America to Africa and Asia.

“We have already seen how mammals around the world are becoming more nocturnal near people, as they try to avoid us during the day,” said Kaitlyn Gaynor, lead author of the 2018 paper, who was not affiliated with the new research. “This [new] study highlights how warming climates may also drive animals into the night.”

Scientists are still learning how these changes will affect wildlife populations — whether, for example, more ibex will get eaten by wolves or have trouble foraging for food in the dark. What’s already clear, however, is that rising temperatures are throwing carefully balanced ecosystems, millennia in the making, out of whack, essentially overnight.

Many animals are becoming night owls

Millions of years ago, most mammals were likely nocturnal, research suggests. One reason? Dinosaurs. Many of these oversized lizards were daytime predators. The only way for mammals to survive was to evolve to become active at night.

Things changed once dinosaurs went extinct, some 65 million years ago. With fewer predators from 9 to 5, mammals were able to colonize the daylight hours, scientists hypothesize, evolving into many of the creatures we know today.

In the centuries since, being active in the daytime — known as diurnal — has been a successful strategy for many species, including the Alpine ibex and humans. Most mammals can see more easily with light. It’s also warmer.

Our actions, however — from farming in ancient grasslands to motorbiking on back-country trails — have begun to change this evolutionary calculus, “driving a global increase in nocturnal activity across numerous mammal species,” the authors of the new study write.

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These shifts are often straightforward. In the mountains of western Colorado, for example, lynx were more nocturnal in areas where people would ski and use snowmobiles during the day. Coyotes and pumas in California’s Santa Cruz Mountains show similar responses where people hike, bike, and walk their dogs.

Yet there are also less obvious forces driving wildlife into the night — namely, climate change. And that, unfortunately, may be a bad thing.

The cost of going out at night

Wild animals, though vulnerable, are incredibly resilient. The fact that many species are becoming more nocturnal suggests that they’re adaptable; they’re finding ways to live, even as we farm, build, drive, and recreate in their homelands. Sure, it’d be better for them if we could simply coexist in our preferred hours of activity, yet that’s not the reality.

For many species that have evolved to be diurnal, however, a nocturnal lifestyle may come at a cost, said Francesca Brivio, the study’s lead author and researcher at University of Sassari. In low light, these animals might have trouble finding food and mates, and avoiding predators, and that could ultimately shrink their populations. If nothing else, these night-shifted creatures “will be outperformed by nocturnal animals that possess sensory adaptations in vision, hearing, and smell for sensing an environment under low light condition,” scientists wrote in a 2018 paper.

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The new study, which tracked ibexes in two national parks, found that the animals would become more active at night, following hot days. In the cool of darkness, these animals are likely able to forage more easily without overheating. But there are certainly drawbacks to this shift. One is that it leaves the goats more exposed to wolves, their main predator. Another is that they can’t see very well, which could impact both their ability to find food and, again, avoid predators.

“For this species, to be nocturnal is a problem — it’s a big problem,” said Stefano Grignolio, another author on the new study and assistant professor at the University of Ferrara.

Nonetheless, foraging at night is apparently still worth it for this species, the study indicates. It seems to be more important that the ibexes roam around when it’s not too hot than that they avoid nighttime activity. (In fact, the researchers compared the activity of ibexes in sites with and without wolves. They found that the goats were more active at night when there were wolves present, indicating that temperature is a more important limiting factor than avoiding the risk posed by predators.)

In other parts of the world, it’s riskier to become nocturnal in response to rising temperatures. A similar study, published in 2020, found that many mid-sized mammals, like zebras, would spend more time foraging at night if there weren’t lions around. In the presence of big cats, they’d be more active during the day, exposing them to a higher degree of heat stress. This means, the authors wrote, that “carnivores limit the capacity of their ungulate prey to adapt to warmer conditions.”

Research like this shows that human activity alters not only the landscape but also what some scientists call the “timescape.” Time, like space, is an ecological resource, during which animals forage, mate, and sleep. And like space, it offers gradients in climate, from the colder hours of the night to the warmer hours of the day. Climate change certainly makes some spaces uninhabitable — by, say, melting ice in the Arctic that polar bears need. Importantly, it is increasingly making certain times of day uninhabitable, too.