Temporary all-male social groups are formed in a number of animal species. We examined 34 years of data collected from 36 male Thornicroft’s giraffe in the Luangwa Valley, Zambia, to test a set of predictions related to five possible functions of all-male herds (predator protection, practicing aggressive skills, prolonging life, nutritional demands and resource learning). We found that all-male herds were significantly smaller than mixed-sex herds, usually contained a mature bull, and were not dependent upon season or habitat. Dyadic