Population-level lateralized feeding behaviour in North Atlantic humpback whales, Megaptera novaeangliae

Lateralized behaviour refers to a preference for using a specific limb or direction of movement that is consistent across events. We investigated apparent lateralized behaviour in North Atlantic humpback whales, Megaptera novaeangliae, in the southern Gulf of Maine using digital acoustic tag (‘DTAG’) technology to analyse feeding behaviours during 2004–2009. An ideal tool to examine lateralized behaviours, DTAGs allowed continuous measurements of whale depth, heading, pitch and roll throughout the attachment period (less than 24 h). Side preference (right or left) in rolling behaviours (e.g. bottom rolling and side lunging) and directional preference (clockwise or anticlockwise) in feeding behaviours such as looping and spiraling were determined from visual examination of DTAG data. A ‘handedness index’ (HI) was used to quantify side bias and strength of preference. We found a population-level right-side bias similar to the 90/10 right-hand bias in humans. Furthermore, photos of jaw scuffing and direct tag data on rolling behaviour were used to assign a bottom-rolling side preference for 11 individuals for whom both of these data were available, 10 (90.9%) of which demonstrated a right-side bias. Consistent laterality was observed between individuals that performed bottom rolling and directional feeding behaviours, which was biased in the right/clockwise direction. Younger individuals tended to show weaker lateralization scores than older individuals, even among adults ( P = 0.048), suggesting that lateralization develops, and continues to do so, beyond sexual maturity. ► Humpback whales showed a 90:10 right-side bias in rolling behaviours similar to humans. ► Humpback whales were clockwise-biased in directional behaviours at the population level. ► Humpback whales showed clockwise directional behaviours despite right- or left-side rolling biases. ► In humpback whales, younger whales showed weaker lateralization than older whales.