For their first 100 million years on planet Earth, our mammal ancestors relied on the cover of darkness to escape their dinosaur predators and competitors. Only after the meteor-induced mass extinction of dinosaurs 66 million years ago could these nocturnal mammals explore the many wondrous opportunities available in the light of day.
Fast forward to the present, and the honeymoon in the sun may be over for mammals. They’re increasingly returning to the protection of night to avoid the Earth’s current terrifying super-predator: Homo sapiens.
My colleagues and I have made the first effort to measure the global effects of human disturbance on the daily activity patterns of wildlife. In our new study in the journal Science, we documented a powerful and widespread process by which mammals alter their behavior alongside people: Human disturbance is creating a more nocturnal natural world.
Many catastrophic effects of humans on wildlife communities have been well-documented: We are responsible for habitat destruction and overexploitation that have imperiled animal populations around the world. However, just our presence alone can have important behavioral impacts on wildlife, even if these effects aren’t immediately apparent or easy to quantify. Many animals fear humans: We can be large, noisy, novel and dangerous. Animals often go out of their way to avoid encountering us. But it’s becoming more and more challenging for wildlife to seek out human-free spaces, as the human population grows and our footprint expands across the planet.
