Evidence for the perceptual origin of right-sided feeding biases in cetaceans.

Foraging behaviour of many cetacean species features the side biases at the population level. The origin of these behavioural lateralisations remains generally unclear. Here we explored lateralisation in aerial display of resident orcas in different behavioural contexts. Side preferences were analysed in lunging during foraging and breaching. One event of each type of displays per individually identified orca was used for analysis. Orcas showed a population-level preference to lunge on the right side when foraging (75% of lunges). In contrast, no lateralisation was found in breaching (54% of breaches to the right, 45% to the left). The right-sided bias in foraging found in orcas is in line with evidence from other whales, both baleen and toothed, and confirms the uniformity of feeding biases among cetaceans. In contrast to breaching, lunging in orcas was associated with fish pursuit, that is, with focused attention to and sensory perception of prey stimulus. The emergence of lateralisation in lunging and the absence of significant bias in breaching suggest that feeding biases in whales are underpinned by sensory lateralisation, that is, by lateralised hemispheric processing of sensory information about the prey. Evidence from orcas may be extrapolated to other cetaceans since right-sided biases in lunging during foraging is a very widespread phenomenon and likely to have a common origin. Our findings support the hypothesis that right-sided feeding biases are determined by left-hemisphere specialisation.