Food transfer in common marmosets: parents change their tolerance depending on the age of offspring

Food transfer is considered to provide infants with additional nutrients during weaning, and in fact, its frequency peaks around this time. However, the mechanisms underlying such food transfer remain unclear. In this study, we investigated whether adult common marmosets (Callithrix jacchus) change their tolerance to offspring begging for food depending on the offspring's age. We used four families consisting of breeding pairs, older offspring (29-49 weeks old), and younger offspring (7-15 weeks old). To directly compare the responses of a parent with its older and younger offspring, we placed one parent and one offspring in a testing space at one time. We presented foods where only the parent could reach them to ensure that the foods were transferred from the parent to offspring. Younger offspring showed more interest in food being held by the parents than older offspring. Parents refused older offspring more frequently than younger offspring and transferred food more often to younger offspring than to older offspring. There was no difference in all behavioral categories between fathers and mothers. These results suggest that both fathers and mothers are more tolerant to weanlings, but their tolerance decreases as offspring mature.