The dominance of one brain hemisphere in the implementation of any function can be manifested in animal behaviour in the form of one-sided preferences, for example, preference to inspect a stimulus with one eye. It was hypothesized that consistent one-sided behavioural bias would make prey species predictable for predators. Therefore, any source of disturbance in nature has to be monitored by both the left and right sensory organs. However, sensory lateralization in antipredator behaviour can occur in other ways, for example, in the lateral biases in the flight initiation distance, latency of the escape response, and intensity of alarm calls. Our study was focused on visual lateralization in the behaviour of social birds and its’ association with the distance to the source of disturbance and flock size.
Observations of the White-fronted geese behaviour were made at spring migration stopovers in the Olonets Region, Karelia, Russia in April – May 2019. During the study, the distance to the flock, the size of the flock, the type of behaviour of the individuals, the wind direction, and the orientation of the individuals in relation to the source of disturbance (motor road) were detected. In total, 88 feeding flocks with the dominance of the White-fronted geese were observed.
There was no significant bias to monitor the road with the left or right eye, but the flocks which used the right eye to observe the road and the flocks with birds oriented in different directions were at greater distances to the road than the flocks which used the left eye. The tendency to monitor the road with the right eye decreased with increasing flock size.
A trade-off between feeding, social and vigilant behaviour in flocks could explain the absence of significant bias to monitor the road with the left eye.The enhanced stress and fear at closer distances to the road may elicit in geese the enhanced use of the left eye for monitoring the source of the disturbance.The more consistent visual bias in larger groups may be a result of the interplay between behavioural lateralization and social pressures.
The study was supported by RSF grant (no.19-14-00119).