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Whether hunting or competing for limited space and resources, humans are the planet's superpredator(捕食者). As the human population expands, it's getting harder for other creatures to find somewhere to hide during the day. Now new findings indicate animals around the world have come up with another strategy: They are becoming nocturnal.

In a [paper](http://science. sciencemag. org/cgi/doi/10.1126/science. aar7121) published in Science, researchers analyzed 76 previous scientific studies about human impact on animal activity. They compared animals' activity during the day and night in areas of high human disturbance (from hunting or farming to hiking and other outdoor recreation) and low human disturbance (relatively natural conditions). The analysis showed animals are becoming an average of 1.36 times more nocturnal due to high human disturbance.

For example, in Poland wild boars go from 48% nocturnal in natural forests to 90% nocturnal in urban areas. Even activities people consider relatively innocuous, such as hiking and wildlife viewing, strongly affected animals' daily rhythms. "We think that we're leaving no trace often when we're outdoors, but we can be having lasting consequences on animal behavior," says Kaitlyn Gaynor, lead researcher for the study.

This is not the first time animals have had to live at night; during the time of dinosaurs, they were also nocturnal. "Dinosaurs were this ubiquitous(无处不在的), scary force, and only after their extinction did mammals(哺乳动物) emerge into the daylight," Gaynor says. "And now humans have taken over and are pushing other animals back into the night."

Scientists suspect becoming nocturnal may hurt those species highly adapted to the sun. They might not be able to live well at night, which would ultimately hurt their chances of survival and reproduction. Perhaps even more alarming effects could be in the wider ecosystem. In California's Santa Cruz Mountains, coyotes have been more nocturnal in response to hikers and have started to alter their diets from daytime prey, such as squirrels and birds, to nocturnal prey, such as rats and rabbits.

Exactly how ecological communities will change, and whether it will be for better or worse, requires further study. Some nighttime shifts may benefit both animals and humans, Gaynor notes. For instance, tigers in Nepal are avoiding potentially deadly conflicts with people as they become more nocturnal.

Studies like this one will eventually help conservation managers make better decisions about how to protect ecosystems. "We'll need to understand local dynamics to really understand how we should be changing management of wildlife populations or human activities," Gaynor notes, "One potential approach might be to manage the timing of human activities so that we leave some of the daylight for other animals."