In the animal kingdom, monogamous mating systems are common in birds, but only in 3-5% of mammalian species. In monogamous mating systems, strong social bonds (pair bonds) exist between male and female members of a pair. Breeding pairs of monogamous budgerigars form strong pair bonds. During the process of pair formation, males imitate the vocalization of their mate, and the pair develops a shared vocalization (contact call). We focus on vocal imitation observed in breeding pairs and are working on the questions of both its function and mechanism.