Why is head position important? It captures the viewers attention and draws them into the image. If the viewer feels the bird is looking at them it is a more dynamic image. The eyes are so important. Here are a couple images of a Juvenile Red-shouldered Hawk to illustrate the concept.
In this image the bird is looking away, the eye does not capture the viewers attention and hold it.
In this image the bird has turned it's head and is looking towards the viewer capturing and holding the attention.
In this image the bird is looking down away from the viewer, it is a pretty bird but does not capture and hold the viewers attention.
In this image the bird is looking up towards the viewer, the image captures and holds the viewers attention. It says I am looking at you.