Bird head stabilization

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. This can be seen clearly in chickens, pigeons, owls and many other bird species. It can also been seen in the natural behaviour of many birds; for example, when they land on a thin branch, or a power or telephone wire, their momentum will often set the branch or wire oscillating back and forth. Yet if one carefully observes their head, by lining it up with a static distant feature of the environment, one can see that it is likewise ‘locked in space’ while compensatory movements of the body and neck are made to balance the bird. Perhaps the most common and obvious example of bird head stabilization can be seen in the ‘head-bobbing’ behaviour of many species of birds as they walk. This is illustrated in Figure 1, where it can be seen in the stroboscopic photo that, while the pigeon’s body moves smoothly forward as it walks, its head is relatively still for several flashes which we call the ‘hold phase’ where stabilization is occurring, and then it is moved rapidly forward (called the ‘thrust phase’) to a new position where again it is stabilized.