Spatial and temporal patterns of lateralization in a parrot species complex

Cerebral lateralization involves information being processed differently by the brain’s two hemispheres and is often associated with behavioural laterality such as preferential use of right or left limbs. Despite having evolved widely in animals, laterality of limb use has been mostly studied in humans and other primates (e.g. handedness) and is relatively poorly understood in other taxa. Perhaps accordingly, the possibility of geographic variation in laterality has been largely overlooked. Foot preferences in parrots have been established as a tractable model for behavioural laterality investigations. Here we tested for geographic and temporal variation in lateralization of foot use in an Australian parrot complex, the crimson rosella ( Platycercus elegans ). We observed lateralization of foot use during foraging in N = 458 wild individuals over nine years, from 42 locations and four subspecies. We show, for the first time to our knowledge in any animal, a cline in laterality. In the morphologically highly variable P. e. adelaidae subspecies, which occupies a marked latitudinal habitat cline, we show that right side lateralization increased at higher (more southerly) latitudes. We also found ambidexterity varied between subspecies, and was present almost exclusively in the morphologically intermediate populations which occupy intermediate habitats, reaching 11% of individuals in one such population. Across all populations, strong lateralization at individual and population levels existed, with 93% of birds consistently lateralized, and 64% using the right foot preferentially. Age, year, season, or whether the bird was perched or on the ground, had no effects on foot preference. Using captive birds, we show that foot preferences were largely stable within individuals over time. Our findings provide rare examples of an intraspecific cline in behavioural lateralization and population differences in ambidexterity, and provide novel support for the hypothesis that ecological factors such as habitat and/or diet influences behavioural laterality within free-living animals.