The Bioacoustics of Blue Whales—Global Diversity and Behavioral Variability in a Foraging Specialist

Abstract

Blue whales are the largest animals ever to inhabit our planet. Worldwide they comprise at least four subspecies, currently recognized to make up to 11 distinct populations which share a krill-specialized foraging preference. The populations are defined by common geography, migratory behavior, and destinations but can also be delineated by unique songs that likely function as a reproductive display. Male singers in each population typically sing the same song type and share some common behavioral patterns in the use of songs and song units. Migratory behavior and characteristics of their habitat shape the differences in the structure of blue whale songs among different populations. Offshore populations tend to have simpler songs than populations occurring more coastally, possibly reflecting differing propagation environments. In areas of high sympatry, such as the Indian Ocean, the increased complexity in song structure may arise as a result of acoustic competition. Both male and female blue whales also produce other sounds, primarily including the so-called D calls, commonly heard associated with foraging behavior. These calls are spectrally similar to foraging signals of other balaenopterids, and eavesdropping may be a mechanism for locating productive areas intra- and interspecies. While some balaenopterids fast on breeding grounds and during much of the migration, blue whales forage along their migration route and in breeding areas, indicating that prey availability is an important driver of their behavior year-round. Fine-scale variability in their acoustic behaviors and relationships to their habitat and prey variability may be the keys that can help us explain the long-term drivers of blue whale population trends. We highlight research questions and possible future directions that would help further enhance our understanding of the interplay between acoustic behavior, diversity, and ecology of this species, along with understanding how some present and future threats, including climate change, may impact the populations of this charismatic species.