The Mighty Hummingbird Can Perceive Motion From Every Angle
Their ability to detect motions from all directions while flying at high speeds makes them a great candidate for podracing.
Hummingbirds live their lives at breakneck speed. They beat their wings 70 to 80 times per second—earning them the "humming" part of their name—and can reach flight speeds of up to 60 mph. They even eat fast. When drinking nectar from a flower they can get 13 licks inside of one second.
Such speedy living (and the ability to hover) also affects how they detect motion. Almost all vertebrates, including humans, are hypersensitive to forward motion that moves from back to front.But ecologists from the University of British Columbia in Canada, have found that hummingbirds see the world in a completely unique way. They detect and pick up on motion from all directions equally—at the same time. Their research is published in the journal Current Biology.
All animals have a region of the brain that detects motion. In mammals, this region is called the nucleus of the optic tract (NOT) and it is responsible for processing visual signals sent to the brain from the retina. Most of the neurons clustered within it are tuned to perceive motion from back-to-front. This means that we pick up more on things coming up from behind, like a predator or some kind of impending collision.
"There are other neurons that would prefer some of the other directions, but it's more than 50 percent of the neurons prefer that forward motion," lead author and zoologist Andrea Gaede explained to Motherboard.
But in hummingbirds, this same motion-detecting brain region—known as the lentiformis mesencephalic (LM) in birds—is instead clustered with neurons designed to pick up many directions of movement. "There wasn't a preference for a specific direction," Gaede said. Each neuron was tuned to something different. "This might make them more aware of motion in any direction around them while they're hovering. This might be another flower or a predator."
This makes sense when you think about the incredibly varied range of motions that hummingbirds perform when in flight. They can fly left, right, straight up, straight down, backwards, forwards, and even upside down. They are also the only vertebrate that can hover in place. And they do it all at a clip. Their high speed courtship displays must be the fastest and most exciting form of flirtation in the animal kingdom.
Gaede and her team discovered this unique ability by tracking the neural activity in the LMs of Anna's hummingbirds and zebra finches as they watched dots move around on a computer screen. The Anna's hummingbirds picked up each direction equally, while the zebra finches focused heavily on the forward direction vertebrates are most commonly attuned to.
Gaede also found that hummingbirds are most sensitive to fast paced motion. "Something moving a small distance, but that is very close to you will actually be a fast paced motion across your retina," she explained—like a fluttering flower, or predator. This could also be a boon when they're locked in aerial combat with other hummingbirds for nectar bearing flowers—a common occurrence amongst the highly antisocial and aggressive little birds.
Gaede hopes to eventually understand how the neural activity in hummingbirds' LM translates into specific in-flight behaviors. You can imagine there's some super fast paced signal processing going on in their little brains for them to be able to blitz through life and respond in kind to other living things of nature moving all around them. Hummingbirds, it seems, are Earth's best candidate for podracing.
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