Temporal Changes in Omura’s Whale Song Off Northwest Australia: Investigating Diel, Lunar, and Seasonal Patterns

Abstract Identifying temporal patterns in song production can provide insight into behavioural ecology of baleen whales, such as reproduction, foraging, and migration. Off northwest Australia, Omura’s whales produce rhythmically repeated two-unit doublet and one-unit singlet vocalisations, characteristic of baleen whale song. This study utilised four multi-year passive acoustic recording sites to analyse the distribution of the Omura’s whale along the northwest coast of Australia and investigate diel, lunar, and seasonal patterns in the species song. Seasonality of doublet and singlet production was compared in the Timor Sea, with doublets accounting for over 98% of the vocalisation counts. Whale song was recorded year-round at two northern sites, with pronounced seasonal and inter-annual variability in acoustic presence. The northernmost site consistently exhibited the highest song rates, often characterised by prolonged periods of overlapping song, suggesting aggregation of multiple vocalising individuals. In contrast, the two southern sites showed reduced or absent detections in winter, suggesting reduced occupancy or singing activity, and potential small-scale northward redistribution during this period. No clear diel or lunar patterns were observed, indicating that song production is unlikely linked to vertical prey migrations. Rather, when song was observed, it was continuous for multiple hours or days. If Omura’s whale song functions primarily as a breeding display, as observed in other baleen species, prolonged singing across diel periods suggests reproductive signalling may occur continuously rather than being constrained by time of day or light conditions. The year-round presence of song supports the hypothesis that Omura’s whales may function as income breeders, relying on consistent prey availability to support prolonged or aseasonal reproduction, with inter-annual variation in song presence potentially reflecting changes in prey resources.