Aggression towards neonates and possible infanticide in the boto, or Amazon river dolphin (Inia geoffrensis)

Recent observed attacks by male Amazon river dolphins on conspecific calves, together with post-mortem examinations, indicate that infanticide occurs in this species but that not all attacked calves are killed. If mortality occurs, it might therefore be an inadvertent consequence of the behaviour rather than the motive for it. Our observations suggest that males who commit infanticide are unlikely to gain direct fitness benefits. Evidence does not fit the sexual selection hypothesis. Aggression towards calves usually ‘drew a crowd’ and may represent socio-sexual display or simply be a form of social pathology, as found in other infanticidal mammals.