In our relatively short time at the top of the food chain, humans have left an impression that will literally last until the Sun swallows the Earth a few billion years from now. But how does our relentless activity impact the creatures we currently share the planet with? A new study has found that mammals across the globe are increasingly turning nocturnal, in a bid to avoid contact with us pesky humans.

Researchers from UC Berkeley and Boise State University set out to study the everyday effects that human activity has on wildlife around the world. To do so, the team conducted a meta-analysis of data on 62 species across six continents, gathered through motion-triggered cameras, GPS, radio collars, and direct observation. The research focused on both carnivorous and herbivorous mammals with body sizes of over 1 kg (2.2 lb), including the likes of deer, coyotes, tigers and wild boars.

"Catastrophic losses in wildlife populations and habitats as a result of human activity are well documented, but the subtler ways in which we affect animal behavior are more difficult to detect and quantify," says Kaitlyn Gaynor, lead author of the study.

The study was looking to see if there was a noticeable shift in the times of day when animals were going about their usual activity, and comparing it to the level of human disturbance in that area. Sure enough, the team found that in response to humans, mammals were on average 1.36 times more nocturnal than usual. In other words, an animal that would normally go about half of its business at night was now bumping that up to 68 percent.

While that might not sound like a huge increase, the consistency with which this occurred was striking. The same pattern can be seen all around the world, in both carnivores and herbivores, and in response to different levels of human disturbance. It wasn't just a matter of animals hiding to prevent being shot by hunters, but they tend to avoid us even during non-threatening activities like hiking or mountain biking, and just while living in residential or agricultural areas.

"While we expected to find a trend towards increased wildlife nocturnality around people, we were surprised by the consistency of the results around the world," says Gaynor. "Animals responded strongly to all types of human disturbance, regardless of whether people actually posed a direct threat, suggesting that our presence alone is enough to disrupt their natural patterns of behavior."

The next question is how much of a problem this trend could pose. The researchers suggest that while there might be some benefits to taking turns sharing spaces, it could be forcing animals into tighter competition, make some more vulnerable to other predators, and disrupting normal feeding and foraging cycles. These questions could be the subject of future work.

"On the positive side, the fact that wildlife is adapting to avoid humans temporally could be viewed as a path for coexistence of humans and wild animals on an increasingly crowded planet," says Justin Brashares, senior author of the study. "However, animal activity patterns reflect millions of years of adaptation – it's hard to believe we can simply squeeze nature into the dark half of each day and expect it to function and thrive."

The research was published in the journal Science.

Source: UC Berkeley