More mammals are becoming nocturnal so they can avoid humans

As Earth’s human population expands, it’s harder for other mammals to avoid people during the daytime. As a result, some mammals are becoming increasingly nocturnal. Nobody knows how that shift will affect individual species and even entire ecosystems. In a new paper in the journal Science, University of California, Berkeley wildlife ecologist Kaitlyn Gaynor and her colleagues examined data on how 62 species across the world spend their days and night. From Scientific American:

For example, leopards in the Central African nation of Gabon are 46 percent nocturnal in areas without bushmeat hunting, but 93 percent nocturnal where the practice is common. In Poland wild boars go from 48 percent nocturnal in natural forests to 90 percent nocturnal in urban areas. Even activities people consider relatively innocuous, such as hiking and wildlife viewing, strongly affected animals’ daily rhythms. Brown bears in Alaska live 33 percent of the day nocturnally when humans stay away, but that number goes up to 76 percent for bears exposed to wildlife-viewing tourism. “We think that we’re leaving no trace often when we’re outdoors, but we can be having lasting consequences on animal behavior,” Gaynor says…

Perhaps even more alarming is the cascade of effects that could occur in the wider ecosystem as animals switch from day to night. “Patterns of competition and predator–prey interactions might change with the nocturnal behavioral changes,” Gaynor says. If one species—say a top predator—starts hunting at night and goes after different types of prey, it will likely have innumerable trickle-down consequences for everything along the food chain. Scientists have already observed such an ecological shift in California’s Santa Cruz Mountains, where coyotes have become more nocturnal in response to hikers. Researchers found these coyotes have started to alter their diets from daytime prey, such as squirrels and birds, to nocturnal prey, such as rats and rabbits.