National News

Mammals Go Nocturnal in Bid to Avoid Humans

Posted June 15, 2018 12:15 p.m. EDT

Humans, it turns out, can annoy more than just one another. In fact, some animal populations are escaping their Homo sapien cohabitants by sleeping more during the day, a new study finds.

Mammals across the globe are becoming increasingly nocturnal to avoid humans’ expanding presence, according to the study, published Thursday in Science magazine. The findings show that humans’ presence alone can cause animals across continents — including coyotes, elephants and tigers — to alter their sleep schedules.

“We’re just beginning to scratch the surface on how these behavioral changes are affecting entire ecosystems,” said Kaitlyn Gaynor, an ecologist and graduate student in environmental science at the University of California, Berkeley, who led the study.

Previous research has found that mammals went from being nocturnal to being active during both day and night about 65.8 million years ago, roughly 200,000 years after most dinosaurs went extinct. “Species for millions of years have been adapting to diurnal activity, but now we’re driving them back into the night and may be driving natural selection,” Gaynor said in an interview.

The researchers compiled data from 76 studies of 62 species living on six continents in reaching their conclusions. On average, human disruption is making these animals 1.36 times more nocturnal, according to the study.

“For example,” it says, “an animal that typically split its activity evenly between the day and night would increase its proportion of nocturnal activity to 68 percent of total activity near human disturbance.”

In California’s Santa Cruz mountains, for example, coyotes are opting to sleep more during the day in response to recreational human activities such as hiking and bicycling. As a result, coyotes are eating more nocturnal prey, whose waking hours match up more closely with theirs. Recent research such as this was used to provide data for the new study, Gaynor said.

Thousands of miles from these night-walking coyotes, tigers living in Nepal at the base of the Himalayas are making similar lifestyle decisions. To avoid contact with humans traversing their favorite forest trails, tigers are increasingly walking the same paths during the night instead, said Neil Carter, who researched this tiger population and co-authored the new study.

This isn’t necessarily a bad thing. “The optimist in me is saying there’s a pathway for coexistence here in an otherwise challenging landscape,” said Carter, an assistant professor at Boise State University. “What we don’t know is how that might negatively affect tigers.”

Future research might strive to show how these animals’ diets, reproductive patterns and mating behavior are being affected by humans, he said.

Humans do not necessarily need to exhibit violent or blatantly destructive behavior to evoke this fear response in animals; often, our simple presence is enough, Gaynor said. Her own research in Mozambique showed that elephants that typically ate human-grown crops, like maize, were avoiding areas that humans inhabit during the day, but came out after sundown in full force.

Gaynor said improving technology, such as infrared cameras that can capture vivid images of animals at night and GPS collars that track their whereabouts, have helped to document the trend toward nocturnal existence.

“Working on this study reminds me that we aren’t alone on this planet,” she said. “Being mindful of the ways our activities are shaping the animals’ habitat will enable coexistence.”