In many mammalian species, animals form subunits within larger groups that are often associated with kinship and/or age proximity. Kinship mediates fission/fusion social dynamics of giraffe herds, but the role of age proximity has been unexamined. Here, we analyze 34 years of data from a population of Thornicroft’s giraffe, Giraffa camelopardalis thornicroftii, living in Zambia in order to assess the extent to which age proximity influences herd composition. We show for the first time that calves born into the same cohort