The ability to invent new solutions to old or novel problems is often equated with intelligence, both in humans and non-human animals. Behavioural flexibility can be defined operationally by looking at the frequency of novel or unusual behaviours, i.e. innovations, in different taxa. Despite the potential survival benefits of behavioural flexibility in the face of changing conditions, there is variation among taxa in the propensity to innovate. Here, I examine in detail one foraging innovation, dunking behaviour (the immersion of food items in water) in Carib grackles (Quiscalus lugubris) of Barbados. I show that the rarity of dunking behaviour in the field is not due to the inability of most individuals to learn and/or perform it, but rather to the balance of costs and benefits not being favourable to its expression in most field conditions. In this population, dunking functions as a proto-tool food-processing technique speeding the ingestion of items that are difficult to swallow. The frequency of the behaviour depends on food characteristics, travel costs between the food source and water, and the probability of losing items to conspecifics. Dunking renders grackles vulnerable to food theft because it involves releasing food items in water, where there is often a build-up of conspecifics. When faced with a high risk of kleptoparasitism, grackles reduce the frequency of dunking, engage in aggressive displays, and keep items in the bill while dunking. Kleptoparasitism not only reduces the rate of dunking by increasing costs to the behaviour, but also by constituting an alternative foraging tactic. The payoffs to this tactic are frequency-dependent; i.e. they decrease as the frequency of kleptoparasites increases in the group. A comparative study on ecological, morphological and behavioural predictors of the occurrence of kleptoparasitic tactics among bird families point to an important role of predation and cognitive abilities in favouring the evolution of kleptoparasitism. Thus, avian food-stealing should not be regarded as a "cognitively simpler" alternative to intelligent behaviour, but as another form of behavioural flexibility. Large-brained primates and birds share the ability to learn quickly, innovate, use tools and engage in exploitative tactics, suggesting that these abilities have not been traded-off against each other, but have instead evolved together.

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