Abstract
Functional lateralisation in the avian visual system can be easily studied by testing monocularly occluded birds. The sun compass is a critical source of navigational information in birds, but studies of visual asymmetry have focussed on cues in a laboratory rather than a natural setting. We investigate functional lateralisation of sun compass use in the visual system of homing pigeons trained to locate food in an outdoor octagonal arena, with a coloured beacon in each sector and a view of the sun. The arena was rotated to introduce a cue conflict, and the experimental groups, a binocular treatment and two monocular treatments, were tested for their directional choice. We found no significant difference in test orientation between the treatments, with all groups showing evidence of both sun compass and beacon use, suggesting no complete functional lateralisation of sun compass use within the visual system. However, reduced directional consistency of binocular vs. monocular birds may reveal a conflict between the two hemispheres in a cue conflict condition. Birds using the right hemisphere were more likely to choose the intermediate sector between the training sector and the shifted training beacon, suggesting a possible asymmetry in favour of the left eye/right hemisphere (LE/RH) when integrating different cues.
Highlights
A large body of evidence has shown that brain asymmetry is not an exclusive peculiarity of the human brain, as lateralisation of brain function has been found to be common across vertebrates [1,2,3,4,5].Due to the lack of the corpus callosum and complete decussation of the optic fibres, the hemispheres of the avian brain are largely independent
We found no significant difference in test orientation between the treatments, with all groups showing evidence of both sun compass and beacon use, suggesting no complete functional lateralisation of sun compass use within the visual system
According to the lateralisation pattern delineated by a number of studies on the visual system of birds, the right hemisphere has an advantage in spatial tasks, in global attention and in social recognition, while the left hemisphere takes the control of behaviours requiring the categorization of visual stimuli and the discrimination of visual details of stimuli [6,9]
Summary
Due to the lack of the corpus callosum and complete decussation of the optic fibres, the hemispheres of the avian brain are largely independent. For this reason, lateralisation phenomena in birds can be investigated by covering one eye so as to largely exclude the involvement of the contralateral hemisphere. According to the lateralisation pattern delineated by a number of studies on the visual system of birds, the right hemisphere has an advantage in spatial tasks, in global attention and in social recognition, while the left hemisphere takes the control of behaviours requiring the categorization of visual stimuli and the discrimination of visual details of stimuli [6,9].
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