Distance and the presentation of visual stimuli to birds

Artificial visual stimuli in the form of photographs, video sequences and computer-generated images are increasingly being used to explore the visual world of birds but their use is controversial as it is still not clear whether birds see them in the same way that humans do. While differences between bird and human colour vision may be one problem with using such artificial images, another and potentially even more important difficulty is the distance at which stimuli are presented. An experiment is described in which hens, Gallus gallus domesticuswere trained to move towards one of two real objects viewed at two different distances. Even for real objects, discrimination levels were better when the hens were allowed to view the stimuli from 5-25 cm than when they were forced to choose at 120 cm and this correlated with their ability to transfer to photographs of the same objects at different distances. In a colour discrimination at a short distance, five out of seven hens showed 100% correct responses when first shown photographs of real objects that they had previously learnt to discriminate. The results suggest that photographs can be used as substitutes for real stimuli but that care should be taken over the distance at which they are presented. The results are discussed in relation to the visual behaviour of birds and differences in functioning of their frontal and lateral visual fields.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour