why birds bob their heads

Birds can fly hundreds of miles a day, and although flight is great for covering long distances, quickly escaping from a predator, or moving between tall trees and buildings, birds also spend a lot of time on the ground hopping, walking, or running.

Seed-eating birds, such as pigeons, chickens, and pheasants, are frequently seen on the ground searching for food and as they walk you will have noticed that many of them bob their heads.

Other families of birds that bob their heads as they walk include the Gruiformes (cranes and rails) and the Ciconiiformes (herons and egrets).

It was first suggested a century ago that head-bobbing in birds was not due to the act of walking itself. In Head Movements and Eye Functions of Birds, a paper published in Biology in 1930 by American psychologists Knight Dunlap and Orval Mowrer, it was shown through a series of photographs that the backward movement of the bob was purely illusory, and that the head moves only forward as the bird walks. During the apparent backward movement, the bird’s head is actually at rest which discounts the theory that it is the bird’s locomotion that causes the head to bob.

Dunlap and Mowrer also found that when birds were blindfolded they did not bob their heads, demonstrating that the head-bobbing is due to some sort of visual stimulation.

However, the idea still held that it was a back-and-forth movement of the head that was important in avian vision.

In 1975, Mark Friedman from the University of Pittsburgh conducted a series of tests on doves, and again showed that although the head moves back and forward with respect to the body, it only moves forward with respect to the environment, also confirming that the movement is most likely linked to vision.

In 1978, a group of researchers from Queen’s University in Canada set out to discover once and for all why some birds bob their heads when they walk.

To conduct their experiment, they first observed feral pigeons walking on flat terrain around the university’s campus. Analysis of film of the pigeons showed that the head bobbing consisted of two phases. One in which the head appeared to be locked in position while the body moved forward, and another in which the head was rapidly thrust forward.

The team then put some pigeons on a treadmill and covered them with a clear plastic box so they couldn’t fly away or walk off the treadmill, while allowing the birds a relatively good view of their surroundings. The idea was that if the pigeons still bobbed their heads when walking on a treadmill then the bobbing was to help them keep balanced rather than anything to do with vision.

After observing and filming the birds, they found that if the birds walked at the same speed as the treadmill, that is stayed still relative to their surroundings, they did not bob their heads, thus proving that the movement is driven by visual cues.

And inadvertently, they discovered something else that reinforced their conclusion. At the end of filming, instead of turning the treadmill off completely, one of the team turned it down to a very low setting.

After a while, the pigeon that remained on the treadmill did something completely unexpected. Although it remained stationary, it continued to push its head further and further forward, without bringing its body forward to catch up, until it eventually toppled over.

Although the treadmill was running at a speed too slow to induce walking, it was fast enough for the pigeon to stabilize its head, even though this resulted in a loss of balance. In other words, the slow slippage of the head position was enough to produce an error in the pigeon’s vision, and so it tried to correct it by moving its head forward.

When birds bob their heads, they are stabilizing the of the world around them. They can momentarily fix their gaze on objects which gives them enough time – about 20 milliseconds – to build a picture of their environment in their brain.

Although it has been suggested that they need to bob their heads to do this because their brains are so small, this is not correct.

Mammals, including humans, also use tricks to stabilize their vision of the world, most notably with tiny muscles that twitch and control the movement of the eyes. You can observe this if you’ve ever watched someone looking out of the window of a fast-moving train.

Birds, however, have very large eyes in relation to the size of their bodies, so although they can move their eyes, the movement is limited. It is far more efficient for them to move their long, flexible necks to keep their eyes stable.

If birds moved their heads and therefore their eyes at the same time as their body their vision would be blurred, and they would have trouble navigating the world.

Experiments on chickens in the 1960s showed that head-bobbing in birds is innate. Chicks begin bobbing their heads at about 24 hours after hatching, and chicks that spent 14 days in a dark room after hatching or had their leg movements restricted showed the same synchronization of head and leg movement as normal chicks of the same age.

Not all birds that walk on the ground exhibit head-bobbing. Ducks, geese, and swans, some owls and birds of prey, and penguins don’t bob their heads. These species all tend to have fairly short, wide-set legs which mean they waddle or take small steps when they walk on the ground, and according to Reinhold Necker who studies avian physiology, a short stride coupled with the position of the eyes on the head may determine why some birds bob their heads when they walk and others don’t.

For example, flamingos and gulls, who walk on the ground and have eyes that have adapted to see across the horizon for predators, do not bob their heads, although black-headed gulls do bob when they are feeding in mud.

So although we know why pigeons and some other species of birds bob their heads when they walk, there are still lots of pieces of the puzzle yet to be discovered.

Pigeons are primarily aerial hunters, so I reasoned that they would need to bob their heads to prevent falling over while chasing hot dog nubs. Actually, it has everything to do with how they view the world and nothing to do with their sense of equilibrium.

Pigeons’ head bobbing allows them to briefly focus their attention on objects. This provides their eyes’ photoreceptors with enough time—roughly 20 milliseconds—to create a stable scene of the sidewalk environment. And this has nothing to do with their bird-size brains.

Vision doesnt mix well with movement. All animals, from insects to eagles, have tricks to stabilize the world. Many mammals, humans included, do this with slight twitches of the eye. This is instinctual, and comes from neuromuscular connections between our eyes and the part of your brain that tracks movement and rotation. Pigeons are able to move their eyes, but their longer, more flexible necks make it more efficient for them to do this motion tracking with their necks.

Of course, many other birds, particularly chickens, jerk their heads as they move. Furthermore, studies that involved blindfolding hens or confining them to a pitch-black chamber have demonstrated that numerous animals utilize head movements to monitor their environment. Additionally, they discovered that the head bobbing was instinctive and appeared 24 hours after hatching.

We know this because in the 1970s a group of researchers put pigeons on a treadmill (covered with a plexiglass box, so the birds couldnt fly away) and observed that their heads did not move when their surroundings were stationary as they walked.

Researchers from Queen’s University in Canada set out to determine why certain birds bob their heads when they walk in 1978.

And inadvertently, they discovered something else that reinforced their conclusion. One member of the crew set the treadmill to a very low setting at the conclusion of filming rather than turning it off entirely.

Birds that consume seeds, like pigeons, chickens, and pheasants, are commonly observed on the ground in search of food. You may have noticed that a significant number of these birds bob their heads while walking.

Therefore, even though we now understand why pigeons and certain other bird species bob their heads when they walk, there are still many unanswered questions.

Birds stabilize the environment around them when they bob their heads. They have the ability to focus their gaze on objects for brief periods of time, about 20 milliseconds, which allows them to create a mental image of their surroundings.