What are birds looking at? Head movements and eye use in chickens

Using video recordings of hens, Gallus gallus domesticus, as they approached different kinds of objects, I examined how change in object distance is associated with a change from lateral to binocular viewing. The birds tended to view distant objects laterally while they preferentially viewed objects less than 20-30 cm away frontally; this was true whether they were looking at another bird or at an inanimate object. However, as well as switching between lateral and frontal viewing, the hens also swung their heads from side to side with movements so large that the same object appeared to be viewed with completely different parts of the retina, and even with different eyes, in rapid succession. When confronted with a novel object, the hens walked more slowly but continued to show large head movements. This suggests that, unlike mammals, which gaze fixedly at novel objects, hens investigate them by moving the head and looking at them with different, specialized, parts of their eyes. Many aspects of bird behaviour, such as search image formation, vigilance and visual discriminations, may be affected by the way they move the head and eyes. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.