Seasonal trends and diel patterns of downsweep and SEP calls in Chilean blue whales (Balaenoptera musculus)

Abstract

To learn more about occurrence and behavior of a recently discovered population of blue whales, passive acoustic data were collected for 15 consecutive months (January 2012 – April 2013) in the Chiloense ecoregion of southern Chile. Automatic detectors and manual auditing were used to detect blue whale songs (SEP calls) and D calls, which were then analyzed to gain insights into temporal calling patterns. We found a year-round acoustic presence of D calls, with the majority occurring during austral summer (December to April), with several sub-monthly peaks. On the other hand, no SEP calls were found during austral winter. Thus, our results support previous studies documenting austral summer residency of blue whales in the Chiloense ecoregion, although they suggest that some individuals remain in the area year-round, highlighting the importance of the Chiloense ecoregion as blue whale habitat. We also investigated daily occurrence of each call type and found that D calls occurred more frequently during dusk and night hours compared to dawn and day periods, whereas SEP calls did not show any significant diel differences. Overall, these findings contribute to a better understanding of occurrence and behavior of endangered Chilean blue whales, which can enhance our ability to develop conservation strategies in this important southern hemisphere habitat.