Animal-borne tags provide insights into the acoustic communication of southern right whales (Eubalaena australis) on the calving grounds

Preferred shallow-water nursery sites provide acoustic crypsis to southern right whale mother-calf pairs

Adaptations to sound production behaviour can reduce the detectability of animal signals by eavesdroppers in a phenomenon known as acoustic crypsis. We propose that acoustic crypsis can include selection of locations that affect how sound transmits through the environment: habitats with poor acoustic propagation can minimize the range of detectability of animal signals. We investigated the potential for the preferred habitats of southern right whales to confer acoustic crypsis. We modelled acoustic propagation and range of detection of calls from southern right whales in the shallow, sandy, near shore waters where mothers and calves aggregate during the calving season. At three nursery sites across three continents in the southern hemisphere, results showed that the depth at which right whales are most commonly sighted has the most limited acoustic detection range for their calls. Thus, these habitats allow mother-calf pairs to remain acoustically cryptic from potential eavesdroppers, both predators and conspecifics, when their calves are the most vulnerable. Our results provide preliminary evidence that, in addition to other behavioural strategies, the use of habitats with poor acoustic propagation can contribute to acoustic crypsis. This adaptation may be a widespread and underappreciated mechanism for avoidance of eavesdroppers.

An overview of North Atlantic right whale acoustic behavior, hearing capabilities, and responses to sound

Creating a baseline understanding of communicative signals and perceptual abilities is imperative for gaining insight into a species' life history. This is especially relevant for at-risk species, as it can aid in monitoring and conservation efforts. Marine mammals communicate predominately through acoustic modalities for a variety of functions, including foraging and reproduction. The acoustic signals produced by marine mammals, and their ability to perceive signals produced by conspecifics, are directly impacted by the level of ambient noise in the underwater environment in which they inhabit. Modern ocean noise levels are considerably louder than historical levels, and noise is therefore considered to be a threat to acoustically communicating marine mammal species. This review summarizes the documented acoustic signals, hearing abilities, and responses to sound of a critically endangered baleen whale, the North Atlantic right whale (Eubalaena glacialis), highlights gaps in the current body of literature, and identifies priorities for future research.

Southern right whale vocalizations on foraging grounds in South Georgia

Southern right whale vocalizations were recorded concurrently with visual observations off the sub-Antarctic Island of South Georgia, and the characteristics of these calls were described. Calls were also compared to those of humpback whales at South Georgia, to determine how the two species might reliably be distinguished acoustically. The southern right whale calls measured (which were all upcalls) had lower frequency with peak energy and were mostly shorter in duration than the calls measured from humpback whales. The frequency upsweep and the lack of harmonics of southern right whale calls were also diagnostic characteristics.