Situation-specificities of Vocalizations in Leach's Storm-Petrel Oceanodroma leucorhoa

The vocalizations of a nocturnally active seabird, Leach's Storm-Petrel (Oceanodroma leucorhoa), were studied at their breeding colony on Daikoku Island, Hokkaido, Japan. Three distinct call types were recognized, namely Chatter-call, Purr-call and Screech-call. All were vocalized by both male and female adults. Purr-call vocalizations and those of Screech-calls showed situation-specificities. In the burrows with Purr-call vocalizations, there were two heterosexual birds, but no broods were found. Therefore, this call may be associated with courtship behavior or pair formation. Screech-calls were always vocalized between two consexual birds and seemed to be vocalized during aggressive encounters. Chatter-calls were usually vocalized together with other call types and in various situations, although the aerial birds vocalized only this call type. But situation-specificities were recognized when these situations were divided according to the calls vocalized with Chatter-calls. Some discussion was made about functional interpretation of vocalizations in Leach's Storm-Petrels.