How Do Hummingbirds Fly Without Crashing?

The birds can master their own physics by sizing up the objects in their path.

Nothing gets between a hummingbird and its nectar. Nothing.

A new study in Proceedings of the National Academy of Sciences reveals that Anna’s Hummingbirds connect different visual cues to keep from crashing into things duiring their high-speed journeys to collect pollen.

Humans, along with many types of flying insects, can calculate how close an object is based on how quickly it passes through their visual field. “A good example of this is when we drive down the road—if it takes some time to pass a building in the distance, we know it’s far,” says Roslyn Dakin, a zoologist at the University of British Columbia and main author of the study.

Anna’s Hummingbirds, however, take a different approach: They gauge the size of the objects in front of them and use that information to steer their movements, allowing them to make split-second decisions and avoid collisions.

To study these reflexes up close, researchers built an 18-foot-long tunnel with a perch on one end and a sugar-water feeder at the other, and attached different patterns to the walls. They then installed eight cameras to record the hummingbirds’ movements.

The videos show the birds veering away when the patterns are vertical and bigger than half an inch (see the clip above). But they don't completely disregard speed either: When moving up and down, they carefully account for how fast they encounter the objects. This technique, known as image velocity, is also used by flies. “This way they can avoid crashing into the ground,” says Dakin. By weighing size and the rate of approach, the animals know exactly when to swerve, while flying vertically or horizontally at speeds of up to 50 miles an hour. Now that's real cruise control.