A report on a characteristic vocalization in Corvus macrorhynchos osai with an indication of vocal learning

In the process of vocal learning, animals give immature vocalization, such as babbling and subsong. Here I report a characteristic vocalization given by a subspecies of large-billed crow, Corvus macrorhynchos osai, that live in Kuroshima Island, Okinawa, Japan. This vocalization (type-K) is characterized by very rapid bill movements (ca. 13 times/sec). The type-K was heard throughout the island, indicating that the population of the Kuroshima Island share this call type. In addition, a juvenile crow was observed giving immature type-K repeatedly. This observation suggests that this call type is not innate but acquired through vocal learning.