If you ever had the time to observe the birds closely, you could have seen their awesome head stabilization too. Besides the swift twitchy head moments, birds tend to keep their head stable for a long time, despite the rapid movement of their body. What’s so special about these moments anyway?
Most birds, unlike humans and other mammals, have their eyes placed on either side of their head. This results in a very wide field of view, and it helps them to scan for any predators or preys in their surroundings. But as their eyes are on the sides rather than being in front, they have a poor binocular vision. And due to such reduced binocular vision, the birds won’t be able to perceive depth of an object so easily.
In order to perceive depth, birds look the object for a while, move a bit, and then again swiftly turn their neck to see the object again to use the two visions as references to understand the depth. The reason why they turn their necks instead of eyes is that they cannot turn them freely.
Several treadmill experiments suggest that most birds like pigeons stabilize themselves by bobbing their head back and forth. This explains why birds like pigeons and chickens have a super cool stabilizing skill. They balance their body as they move by stabilizing their neck by holding their vision locked to an object. This is regarded as an optokinetic response. There are two phases observed in such a movement.
When the bird looks at an object while they move, they fixate their vision on that particular object for a while to get a clear view of it. This is called as the hold phase. When the rest of the body catches up and the bird moves, the bird then makes a sudden saccade eye moment-by turning the neck-to fix on a different object to compare the information and perceive depth. This is called as the thrust phase.
While the reasons for these rapid movements are still unclear, the most common explanation for this behavior in birds is that their long necks aid in moving their eyes swiftly to balance themselves and perceive depth.
Eagles and Owls have forward facing eyes and they have a very good binocular vision.
Owls can turn their necks up to 270 degrees.
US Navy tried to weaponize Pigeons in the early 1940s.