A first description of rhythmic song in Omura’s whale (Balaenoptera omurai)

Omura’s whale is a recently described tropical Balaenopterid whale with virtually nothing known about their acoustic behavior. Recordings have revealed a stereotyped 15-50 Hz amplitude-modulated vocalization, rhythmically repeated in a typical Balaenoptera song manner. In order to describe the characteristics of the song, continuous recordings were made using archival recorders during 21 days at 4 sites off the northwest coast of Madagascar in documented Omura’s whale habitat. A total of 926 hours of recordings were manually browsed to identify all occurrences of the song vocalizations, logging 9117 individual song units. Occurrence varied among sites spread across 40 km of shelf habitat, indicating heterogeneous distribution of whales and use of habitat over space and days. Diel variation indicated higher incidence of song during daylight hours, counter to trends found in other Balaenopterid whales. A total of 215 different individual series were identified ranging from 3 to 252 consecutive song units. For 121 individuals with more than 20 consecutive song units, the interval ranged from 147.4 s to 289.0 s with a mean of 200.3 s (s.d. 25.9), and recorded song duration ranged up to 13.33 hr. This represents the first description of singing behavior for this species, suggesting a time-intensive behavioral display likely related to breeding.