Sexual dimorphism in beak size may have affected behaviour. Such dimorphism is common in other parrots, for example in the palm cockatoo and the New Zealand kaka. In species where it occurs, the sexes prefer food of different sizes, the males use their beaks in rituals, or the sexes have specialised roles in nesting and rearing. Similarly, the large difference between male and female head size may have been reflected in the ecology of each sex, though it is impossible to determine how.