Lateralisation of trunk movements in captive Asian elephants (Elephas maximus).

Behavioural lateralisation has been widely investigated in vertebrates. Most studies in this area have focused on laterality in paired organs such as hands, limbs, and eyes. Fewer studies have explored side preferences in unpaired organs such as tails or trunks. We investigated laterality of trunk use among captive Asian elephants (Elephas maximus), quantifying side preference in four different trunk movements: feeding, sand spraying, self-touching, and swinging. We found evidence for significant side preference in all four movement categories. Variation in the occurrence and direction of side preference was seen both within and between individuals but no overall population-level side bias was seen for any of the four trunk movements. The strength of side preference in trunk use was significantly higher for feeding than for self-touching and swinging. This study adds to the very limited data on laterality in unpaired organs generally, and elephants' trunks more specifically. In addition it provides novel information about directional lateralisation in trunk use across a range of functionally distinct contexts.