Ethical Note
Although feeding platform experiments induce contest competition and rates of agonistic behaviour (primarily in the form of low-intensity aggression or, most often, spatial displacements without overt aggression) above baseline levels (Di Bitetti and Janson, 2001, Janson, 1996 and Wheeler and Tiddi, nd), intense aggression at the platforms was rare and we did not observe any cases of aggression at platforms that led to physical injuries in the study subjects. Furthermore, the experiments did not induce increases in physiological stress in the subjects (see Results). All aspects of the study were approved by the Animal Welfare Officer at the German Primate Center and by the Argentine Administration of National Parks (permit no. NEA 142), and adhered to the legal requirements of Argentina.