On a sunny morning in October 2014, Christopher Schmidt strolled onto the grassy fields of Magazine Beach, a public park along the Charles River in Cambridge, Mass. To get a better view of the fall scenery, he launched his drone, a DJI Phantom quadcopter equipped with a camera.

Then he saw it: a juvenile red-tailed hawk circling nearby. Within seconds, it swooped down — wings outstretched, tail flared, talons open — and flipped the drone midair. Mr. Schmidt cut the propellers, and the bird flew off, apparently uninjured. The drone dropped to the ground, undamaged except for a slight bend in its plastic landing gear.

Mr. Schmidt, a 31-year-old software developer, posted a drone’s eye video of the encounter on YouTube. It has been viewed about five million times. And it is hardly the only evidence of conflict between animals and so-called unmanned aerial vehicles.

In other videos, ospreys, magpies, sea gulls and geese pursue and attack drones in flight. With a hop and punch, a kangaroo knocks one to the ground. A cheetah chases, leaps and swipes at one. A pugnacious ram head-butts a drone that hovers too low. And a particularly defiant chimpanzee at a zoo in the Netherlands whacks a buzzing intruder out of the sky with a branch.