Visual lateralisation of swans in response to anthropogenic disturbance differs according to observation task, presence of chicks and type of locomotion

Visual lateralisation is manifested in the dominance of one brain hemisphere in the processing of information from one of the eyes. Most studies manifested that the right hemisphere is responsible for the aggression, fear, and detection of predators and other threats, and the left hemisphere is responsible for the positive emotions, food search, and detection of large changes in the environment. Nevertheless, some independent studies manifested the opposite biases in the same behaviour tasks. To evaluate the value of species, behaviour task, locomotion type and breeding status in visual lateralisation biases we studied the behaviour of swimming and flying Whooper swans and Bewick's swans with and without chicks when observing a source of danger and a partner. We found that in the same conditions, the visual lateralisation bias was identical in two species and it differed depending on the type of locomotion in one species. Birds had a significant bias in the observation of the source of disturbance and hadn't in the observation of the leading partner. The presence of chicks strengthened the manifestation of visual lateralisation in the following birds. Therefore, special attention should be paid to details in comparing the results of studies conducted under different circumstances.