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Humans are influencing the behavior of wild animals, causing them to flee daylight and seek the cover of darkness for protection, according to a new study from UC Berkeley.
The study, published Thursday in the journal Science, offers powerful evidence that fearful animals are shifting their activities from daytime to night, when humans are quietly home in bed.
“As the planet grows increasing crowded, this represents a way for animals to adapt, living along humans,” said study lead author Kaitlyn Gaynor, a Berkeley PhD candidate with UC’s department of Environmental Science, Policy, and Management. But there may be profound ecological consequences, she warned.
It’s been well established that humans are causing shifts in where animals live. But this large-scale analysis of 76 studies of 62 species of large mammals from six continents represents the first effort to quantify the global effects of human disturbance on the day-to-day routines of wildlife – when they feed, mate and care for their young.
On average, mammals were 1.36 times more nocturnal where there was human disturbance, the study found. An animal that naturally splits its activity 50-50 – half day, half night — increased its nighttime activity to 68 percent and reduced its daytime activity to 32 percent.
These studies monitored animal activity using tools such as GPS trackers and motion-activated cameras. The researchers then used the information to compare the nighttime activity of each species during seasons of high and low human disturbance.
The finding was consistent across carnivore and herbivore species of all body sizes greater than 2.2 pounds.
The research included studies of common Bay Area species such as coyotes. Very adaptive wild canines, coyotes have different strategies depending upon where they live: In the wild, they tend to hunt in the day; in urban settings, they’re more likely creatures of the night.
But it documents similar changes in behavior among threatened species in exotic locales. In Nepal, where tigers and people use the same forest trails, tigers are become more strictly nocturnal. So are Sun Bears, which once roamed Sumatran rain forests in broad daylight.
“Given the continuing increase of the global human footprint, the study is timely and of paramount importance for understanding the influence that humans may have on the behavior of diurnal, twilight-active and nocturnal wildlife,” wrote Ana Benitez-Lopez of the Department of Environmental Science at Radboud University in the Netherlands, in an accompanying commentary in Science.
The shift in animal behaviors may have a positive side, helping humans and animals coexist, noted co-author Justin Brashares, a professor in UC’s department of Environmental Science, Policy, and Management, but perhaps not enough.
“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,” he said, in a statement.
Shifts in behavior may cause animals to feel stress, becoming more vigilant or eating less, according to the team. There may be biochemical and reproductive disturbances, lowering their survival rates and threatening entire species.
There also may be broader ecological consequences. The diminished ability of some top predators to hunt at night by impair their role as ‘top-down’ predators, changing the predator-prey relationships, Benitez-Lopez noted. And when prey become nocturnal to avoid humans, they may suddenly find themselves vulnerable to other night-dwelling creatures.
This pattern held no matter what the type of human disturbance, whether activities such as hunting, hiking and mountain biking or building roads, home construction and farming, the research found.
The findings can be used to inspire greater thoughtfulness in how we use our wild areas, said Gaynor. Perhaps certain parts of parks should stay completely off-limits to humans and their pets, or perhaps parks could impose restrictions on what time of day human activities are allowed, she suggested.
“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,” said Gaynor. “Animals responded strongly to all types of human disturbance, regardless of whether people actually posed a direct threat.
“Our presence alone is enough to disturb patterns of behavior,” she said. “Even ‘leave no trace’ backpacking can have a lasting impact.”
