According to a new study carried out by ornithologists at the University of British Columbia, Canada, hummingbirds are surprisingly sensitive to movements in their visual field and direct flight to respond to those movements.
The volcano hummingbird (Selasphorus flammula), a tiny bird that is a resident breeder in the highlands from Costa Rica to Panama. Image credit: Dick Daniels, www.carolinabirds.org / CC BY-SA 3.0.
The bird brain has numerous specializations for navigation and processing visual information, but relatively little is known about how flying birds control their position in space.
To study the role of vision in controlling hovering flight, Dr Benjamin Goller and Dr Douglas Altshuler of the University of British Columbia’s Department of Zoology developed a virtual reality environment where visual patterns could be displayed to a freely flying hummingbird.
In a laboratory flight arena, the bird hovered around a plastic feeder while images were projected on a surface behind the feeder.
The hummingbird’s near 360-degree peripheral vision gives it a big viewing window around the feeder and its reaction to projected moving images surprised the team.
Even minimal background pattern motion caused the hummingbird to lose positional stability and drift.
Giving the bird time to get used to the stimuli didn’t eliminate the disruption.
“We were very surprised to see how strong and lasting the disruption was – birds with hovering and feeding abilities fine-tuned to the millimeter were off the mark by a centimeter,” said Dr Goller, who is a co-author of the paper published in the Proceedings of the National Academy of Sciences.
“We think the hummingbird’s brain is so precisely wired to process movement in its field of vision that it gets overwhelmed by even small stimuli during hovering.”
It’s the first time ornithologists have directly measured the impact of moving visual patterns on free flight in birds.
“Despite the urge to feed, the hummingbirds seemed unable to adapt to the moving images. It suggests their visual motion detection network can over-ride even a critical behavior like feeding,” Dr Goller said.
Dr Altshuler added: “now we want to investigate how birds use vision during transitions from mode to mode, for example as they move from hovering to forward flight.”
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Benjamin Goller & Douglas L. Altshuler. Hummingbirds control hovering flight by stabilizing visual motion. PNAS, published online December 8, 2014; doi: 10.1073/pnas.1415975111
