Fear of humans is driving animals into the darkness — and nocturnal life

Animals who can't avoid humans during the daytime take to the night-life
To avoid humans, animals are becoming less active during the day — when humans are out and about — and more active during the night. (Laurent Geslin)
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It may come as a surprise that many animals, including some apex predators, are terrified of humans. According to scientists, it's because we're big and loud and 'novel' to them. And so to protect themselves, they try to avoid us as much as possible.

But as we continue to push the boundaries of our existence and encroach on animals' natural habitats, it becomes inevitable that we will encounter them. To counter this, researchers have found, animals are changing their behaviour and are becoming less active during the day — when humans are out and about — and more active at night.  

We thought animals would be most scared by really threatening activities like hunting, but animals responded to all forms of human disturbance whether or not we posed a threat.- Kaitlyn Gaynor

Animals are joining the ranks of night owls

Kaitlyn Gaynor, a wildlife ecologist and a PhD candidate at the University of California Berkeley, has been studying this phenomenon, and thinks this shift to nighttime activity could hurt some animals.  

"My collaborators and I noticed that animals seem to be more active at night when they're around people," says Gaynor."Once this idea was on our radar, we began to see it throughout the published scientific literature as well, and it seems to be a fairly common global phenomenon."

The sun bear, a native species of Southeast Asia, is exclusively diurnal under natural circumstances, but flipped to nocturnal after encountering human researchers. (Connormah, cc-by-sa-2.0)

To study this, she dug into 76 studies looking at 62 species of mammals from six continents and their response to human activities. The animals ranged from medium-sized mammals like the common opossum all the way up to the African elephant, and spanned every continent except Antarctica.

She looked at the degree of disturbance the animals were exposed to, including high levels of disturbance like urban development or hunting, or low levels like hikers in wilderness areas.  Surprisingly she found that the level of disturbance didn't matter.

"They're scared of us no matter what," says Gaynor. "We thought animals would be most scared by really threatening activities like hunting, but animals responded to all forms of human disturbance whether or not we posed a threat."

One example she points to is the sun bear of the Sumatran rainforest. The human disturbance in this instance was, ironically, researchers who were trying to study the animal. But their presence led to a dramatic shift in the bears' behaviour.

"They were almost exclusively diurnal which flipped to become almost exclusively nocturnal around people," says Gaynor.

How nocturnality affects animals

Across all the case studies, she found 83 per cent of them documented some shift towards nocturnality. Overall, animals became 1.36 times more nocturnal in areas of human activity as compared to more natural conditions. That means if an animal typically splits its activity 50/50 between day and night, it would increase its night time activity to 68 per cent around people, and spend only 32 percent of its time active during the day.

We may see natural selection select for traits that enable wildlife to be more successful at night if that's becoming their dominant behaviour.- Kaitlin Gaynor

This dramatic shift will likely cost animals who are ill-adapted to the dark, says Gaynor, by making it harder for them to find food, mate, and avoid predators. But for species who are better adapted to nocturnal activity - tigers would be one example - it could be a positive for both humans and animals.

"Tigers are becoming more strictly nocturnal around people," explains Gaynor. If they're able to thrive in the nighttime and carry out their activities as usual, this could make it safer for both parties and lead to a happy coexistence.

European beaver in the city center of a big town in France. (Laurent Geslin)

For species that do not adjust well, Gaynor says we may have to get creative about giving them space by restricting human activities to certain times of the day.

In the grand scheme of things, this could also lead to major changes in the evolution of animals, adds Gaynor. "We may see natural selection select for traits that enable wildlife to be more successful at night if that's becoming their dominant behaviour."