Hummingbird
vision wired to avoid high-speed collisions
UNIVERSITY OF BRITISH COLUMBIA
Hummingbirds are among nature's most agile fliers. They can
travel faster than 50 kilometres per hour and stop on a dime to navigate
through dense vegetation.
Now researchers have discovered that the tiny birds process
visual information differently from other animals, perhaps to handle the
demands of their extreme aerial acrobatics.
"Birds fly faster than insects and it's more dangerous if
they collide with things," said Roslyn Dakin, a postdoctoral fellow in the
UBC's department of zoology who led the study.
"We wanted to know how they
avoid collisions and we found that hummingbirds use their environment
differently than insects to steer a precise course."
Note: Watch a video of the experiments here: https://youtu.be/6Z45BaswaOs
Scientists at UBC placed hummingbirds in a specially-designed tunnel and projected patterns on the walls to figure out how the birds steer a course to avoid collisions when they are in flight. They set up eight cameras to track the movement of hummingbirds as they flew through a 5.5-metre long tunnel.
"We took advantage of hummingbirds' attraction to sugar
water to set up a perch on one side of the tunnel and a feeder on the other,
and they flew back and forth all day," said Douglas Altshuler, associate
professor in the department of zoology. "This allowed us to test many
different visual stimuli."
While not a lot is known about how birds use vision in flight,
it is known that bees process distance by how quickly an object goes past their
field of vision, like we do as we drive down a road.
As we pass by telephone
poles on the side of the road quickly, our brains understand that the objects
are nearby; buildings in the distance will take some time to pass, letting us
know they are further away.
When scientists simulated this type of information on the tunnel
walls, the hummingbirds didn't react. Instead Dakin and her colleagues found
that the birds relied on the size of objects to determine distance.
As
something gets bigger, this may signal to the birds that they are getting
closer, and as something gets smaller, it may signal that they are moving
farther away.
"When objects grow in size, it can indicate how much time
there is until they collide even without knowing the actual size of the
object," said Dakin. "Perhaps this strategy allows birds to more
precisely avoid collisions over the very wide range of flight speeds they
use."
The researchers also found that the hummingbirds used the same
technique as flies, known as image velocity, to assess their altitude. When the
patterns on the walls simulated going up and down, the researchers found that
the birds adjusted their flight.
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The study was published today in the Proceedings of the
National Academy of Sciences:http://www.pnas.org/lookup/doi/10.1073/pnas.1603221113 (link may not be immediately available).
Photos and videos of the study are available: https://drive.google.com/folderview?id=0B3RpD6FYqJZTV00zak8zWXNNdmM&usp=drive_web