How can a Common Kingfisher bird balance on a tiny swaying reed without moving its head?
This is a one minute video of a Common Kingfisher bird standing on a tiny reed swaying in the wind. It's from the BBC Network in England.
For much of the video, especially the beginning, the bird doesn't seem to be moving its head, but the body is moving back and forth on the reed. Even when it moves its head a bit, the body still appears almost independent, and its feet don't move from their original position.
I initially thought it was fake, that the picture of the head had been manipulated to stay still while the body moved, at least for parts of it. It's obviously real, though, but I still don't understand the mechanism.
How does a Kingfisher literally sit on that tiny moving reed without moving its head, and why? Is it asleep?
This post was sourced from https://outdoors.stackexchange.com/q/21000. It is licensed under CC BY-SA 4.0.
2 answers
This is called gaze stabilization and birds do it to keep one thing in focus even while their body is moving.
What is head stabilization in birds? When the body of a bird is held in the hand and rotated or moved in different directions the head often appears ‘locked in space’ or glued to the spot, and does not move with the rest of the body. To maintain this stable position the bird has, of course, to make complex compensatory movements of the neck.
Thanks in part to a large number of vertebrae and muscles in their neck, birds can hold their head in place even when their body’s in motion. According to David Lentink, an assistant professor at Stanford University who studies biological flight, this adaptation helps birds stream high-resolution visuals when moving quickly through complex terrain. “They keep their head absolutely horizontal at all cost because that way they have the most reliable information, which they have to stream at high rates,” he says. “When you’re maneuvering like crazy . . . you need a perfect vision platform.”
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Gaze stabilization in birds is complex and still poorly understood, Lentink says. But what we do know is that it’s controlled in part by visual input and the vestibular system, a sensory system in the inner ear in charge of balance and spatial orientation. Like a three-dimensional level, the vestibular system (which other vertebrates have, as well) governs spatial orientation, and it’s critical for keeping the head steady.
For Birds, a Steady Head Is the Key to Incredible Focus
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You asked two questions: How does it balance, and why does it do this? Charlie answered "Why does it do this?", and he did so quite well, especially since, as his sources suggest, even the biologists do not completely understand it yet.
As for how it balances...
It does indeed appear at first to defy gravity. The birds center of mass is moving relative to the platform it is standing on, and it looks like it is moving in the wrong direction, since the head and neck are extending out away from the direction of movement of the twig (indeed, they would have to in order to keep the head still relative to the environment).
However, after watching that animation play through many times I have convinced myself that the bird is indeed moving other parts of its body to compensate. It does move its legs, its belly, and other body parts at times in order to compensate for the motion and thereby balance itself.
It does not look like it, but the body motion is there. It is just very difficult to see unless you are specifically looking for it, and even once you spot it the balancing motions are very, very small.
It is like when we stand in one place, we have to keep adjusting our bodies constantly to not fall over. We do it without even thinking about it. This is even more amazing in the case of the bird since it has to not only stay upright but do so against the motion of the twig; however, the mass of the neck and head is probably very, very small proportional to the mass of the rest of the body which is doing the balancing, and that would mean that the rest of the body does not need to move much.
And that seems to be how the bird is balancing on the twig while keeping its head like that. At least, I have convinced myself as much by watching that animation replay too many times. ;)
This post was sourced from https://outdoors.stackexchange.com/a/21013. It is licensed under CC BY-SA 4.0.
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