Hummingbirds are known to be among the natural world’s fastest fliers, able to travel more than 50 kilometers per hour and stop abruptly to navigate through foliage.
Roslyn Dakin, lead author and a postdoctoral fellow in the Department of Zoology at The University of British Columbia, said,
We wanted to know how they avoid collisions and we found that hummingbirds use their environment differently than insects to steer a precise course.
Dakin’s team put hummingbirds inside a specially designed tunnel and projected some patterns on the tunnel walls to determine how the tiny birds would steer a course to avoid colliding with things in flight. The researchers placed eight cameras to track the birds’ movements as they flew through the 5.5-meter long tunnel.
Douglas Altshuler, associate professor at the UBC’s Department of Zoology, explained that they set up a perch with sugar water on one side of the tunnel and a feeder on the other so the hummingbirds would fly back and forth. “This allowed us to test many different visual stimuli,” he said.
While there is a lack of information on how birds use vision when flying, scientists have already discovered that bees are able to process distance by how quickly an object goes by in their field of vision, similar to how humans process distance when driving.
When the researchers used this same observation on the hummingbird tunnel, the birds did not react as thought. Instead, the team found that the hummingbirds relied more on the size of objects to determine distance. As something gets larger, it is a signal that it is getting closer, and as something gets smaller, it is a signal that it is farther away.
Dakin said that this difference in size may be the birds’ indication for knowing how much time they have until they run into it, even if they don’t know the actual size of the object. “Perhaps this strategy allows birds to more precisely avoid collisions over the very wide range of flight speeds they use,” she added.
The researchers also discovered that the hummingbirds used the same method as flies, which is called image velocity, to gauge their altitude. When the researchers adjusted the patterns on the walls to simulate going up and down, the hummingbirds adjusted their flight accordingly.