Leaving by staying: Social dispersal in giraffes

Young giraffes can leave their childhood community without moving far away. Some young males began associating with a different set of adult females while remaining close to where they had grown up. Because giraffe communities can overlap on the ground, changing social membership need not require a journey into unfamiliar country.

Monica Bond, Derek Lee and colleagues traced 67 male and 70 female giraffes first photographed as calves in Tanzania's Tarangire ecosystem. Across seven years, they compared two kinds of departure: moving beyond the typical reach of an adult female's home range, and switching from the female community associated with the calf's early life to another community. Repeated photographs supplied both locations and the identities of companions.

Sixty-nine percent of males dispersed in at least one sense, compared with 26% of females. Twelve of the 46 male dispersers changed communities without making the larger spatial move. Most departures occurred around four years of age. Joining another community could offer unrelated mates without sacrificing familiar terrain, but the study did not test mating success or relatedness. Its clearest lesson is simpler: measuring distance alone would miss some of the departures in a young giraffe's life.