Competition for a desired food in family groups of the common marmoset (Callithrix jacchus) and the cotton-top tamarin (Saguinus oedipus).

Four captive groups of common marmosets (Callithrix jacchus) and three groups of cotton-top tamarins (Saguinus oedipus) were each presented with a desired food and their consumption was monitored. Inequalities in consumption between individuals were found for each group of each species. Generally, adult females consumed most of the desired food, followed by juveniles, and finally adult males. High consumption levels by all individuals during isolated feedings indicated that consumption inequalities within groups were most likely due to competition rather than inter-individual preference differences. Aggressive defense of the food cup was performed most frequently by adult females in both species. In Callithrix jacchus groups, this aggression was most often directed against adult males, but in Saguinus oedipus groups, it was most often directed against juveniles. Modification of the method of food presentation, such that food was more dispersed, lessened, but did not eliminate, inequalities in consumption.