Sunlight and time of the day affect visual lateralisation in Greater White-fronted Geese

Sensory lateralisation, defined as the separation of functions for processing information from the sensory organs between the hemispheres of the brain, is a variable characteristic of the nervous system influenced by external factors. The plasticity of lateralisation is an important factor influencing the assessment of lateralisation on individual and population levels. We tested the influence of sunlight and time of the day on the visual lateralisation of Greater White-fronted Geese Anser albifrons when following their partners. Most of the individuals showed no preference to observe a partner with one of their eyes. Among the lateralised birds, a significant prevalence of right-eyed individuals was revealed. The highest proportion of lateralised individuals was observed in cloudy conditions. Direct sunlight, particularly in the morning, interfered with the emergence of visual lateralisation. Thus, the effect of sunlight and time of the day on lateralisation in birds should be taken into account when evaluating lateralisation in field observations and experiments.