Juvenile rhesus macaques (Macaca mulatta) dramatically increased their reconciliation rates after being transferred into a group of the more conciliatory stumptail macaques (Macaca arctoides).
Notes on verification
This is a well-established finding from de Waal & Johnson (1986) and subsequent work (de Waal, PNAS 1993 'Cultural transmission of a social custom'), widely cited in primatology as evidence for social learning of conflict-resolution behavior across species. Multiple independent citations corroborate the core finding, though exact wording ('dramatically') may vary by source.