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Human activity is causing more and more animals to embrace the night

As humans encroach more and more on wildlife habitats, animals are finding that the best way to survive isn’t to pack up and move—it’s to embrace the night life. That’s the conclusion of a new study, which shows that a variety of previously diurnal animals such as foxes, deer, and boars have become nocturnal to avoid human activity out of fear. But this nighttime switch comes with its own risks.

To conduct the work, researchers analyzed 76 studies that looked at how 62 species of mammals on six continents—from opossums to elephants—changed their behavior in response to human activities such as hunting, farming, and development. The studies utilized various technologies to follow the animals, from GPS trackers to motion-activated cameras.

Once night falls, the animals surveyed became far more active than they were before humans arrived, hunting and foraging in the dark. For example, mammals that used to split their activity evenly between day and night typically increased their nighttime activity to 68%, the team reports today in Science.  

The team also found the animals responded similarly to these human encroachments, regardless of whether human activity directly impacted them. So, a deer might become more active at night simply because it sees humans hiking nearby, not because it’s being hunted.

The researchers believe these nocturnal behaviors not only allow humans and animals to coexist more peacefully, they may be able to give us hints as to how to plan conservation efforts accordingly, such as restricting human activity during times when a specific species is more active. But moving to the nightlife could also have downsides for these animals. A nocturnal lifestyle can decrease an animal’s ability to hunt and forage successfully and can even impact its ability to find a mate. Switching to a nocturnal lifestyle can affect natural patterns of life even if these animals are doing so to reduce their interaction with humans. So, just because animals are becoming more active at night doesn’t mean they’ve escaped the impact of humans.