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More Animals Becoming Night Owls, Thanks to Humans

As people increasingly encroach on animal habitats, more wild creatures are taking refuge in the night.


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A day in the life of a sun bear is what you might expect from the name: sunny. In its natural habitat, the sun bear spends over 80 percent of its active waking time in daylight.

But when disturbed by human activity, that changes dramatically. In areas where people are pushing into the sun bear’s domain, the animals are spending 90 percent of their waking time after dark, according to a study published in June in the journal Science. Effectively, the threat of human presence is making the sun bear nocturnal.

Led by scientists at the University of California, Berkeley, and Boise State University, the study found that human activity is driving scores of mammals to shift their activity from the day into the dark hours of the night. With many species already pushed to the geographical margins of their local habitats, the animals are attempting to avoid interaction with humans by “separating themselves in time rather than in space,” the study authors write. (Here’s how some wild animals are hacking life in cities.)

How mammals spend their waking time


When disturbed by humans

When disturbed
by humans

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For the work, the researchers examined the behaviors of 64 mammal species, including deer, tigers, boars, and, of course, sun bears. They observed increased nocturnal behavior in a large majority of them, with species that are naturally active during the day tending to shift their activity to after dark, and those that are naturally nocturnal becoming more so. The mammals affected ranged across body size, habitat type, region of the world, and diet.

Human activity of all sorts had an impact, including lethal activity like hunting as well as agriculture and land development, harvesting local natural resources, and even hiking or walking through wild areas. For example, sport hunting in the Hwange National Park in Zimbabwe drove sable antelopes to spend more of their active waking hours at night, restricting their access to water during the day. Similarly, hikers in the Santa Cruz Mountains in California made coyotes more nocturnal, forcing them to find new sources of food among traditionally nocturnal prey.

The study authors warn that profound shifts in the natural behavior patterns of so many species disturb predator-prey dynamics that have evolved over generations, leading to unknown and potentially cascading effects on the environment.

“We really don’t know,” says lead author Kaitlyn Gaynor of UC Berkeley. “Entire ecosystems might be reshaped by this behavior.”

Source: Katilyn Gaynor, UC Berkeley