How Hummingbirds Change Mental Gear in Flight

Hummingbirds use two distinct sensory strategies to control their flight, depending on whether they are hovering or moving forward, according to a new study led by zoologists at the University of British Columbia (UBC).

“When fighting forward, hummingbirds rely on what we call an ‘internal forward model’ – almost an intuitive, ingrained autopilot – to judge speed,” says Dr. Vikram B. Baliga, lead author of a new study on hummingbird locomotion published in Proceedings of the Royal Society B. “There is simply too much information coming in to rely directly on every visual cue in your environment.”

“But when they are hovering or processing signals that might require an altitude change, we found that they rely much more on direct, real-time visual feedback from their surroundings.”

The results not only provide insight into how tiny, agile birds perceive the world during in-flight transitions, but could also inform on-board navigation programming for next-generation autonomous flying and gliding vehicles.

Colibri flight recorder

The researchers asked hummingbirds to make repeated flights from a perch to a feeder in a four-meter tunnel. To test the birds’ response to various visual stimuli, the team projected patterns onto the front and side walls of the chamber. Each flight was filmed.

In some scenarios, the researchers projected vertical stripes moving at different speeds onto the side walls to mimic degrees of forward motion. Sometimes horizontal stripes on the side mimic changes in altitude. On the front wall, the researchers projected rotating vortices, designed to create the illusion of changing position.

“If birds were directly inspired by visual stimuli, we would expect them to adjust their forward speed to the speed of the vertical stripes on the side walls,” says Dr. Baliga. “But even if the birds changed speed or stopped completely based on the patterns, there was no clear correlation.”

However, during flight, hummingbirds adapt more directly to stimuli indicating a change in altitude. And while hovering, the birds also worked to adjust their position much more closely to the changing spirals projected by the research team onto the front wall.

“Our experiments were designed to study how hummingbirds control flight speed,” says Dr. Doug Altshuler, lead author of the paper. “But because hummingbirds took spontaneous pauses to hover during their flights, we discovered these two distinct strategies for controlling different aspects of their trajectories.”