Friend or foe: Risso’s dolphins eavesdrop on conspecific sounds to induce or avoid intra-specific interaction

Abstract

The detection and use of emitters' signals by unintended receivers, i.e., eavesdropping, represents an important and often low-cost way for animals to gather information from their environment. Acoustic eavesdropping can be a key driver in mediating intra-and interspecific interactions (e.g., cooperation, predator-prey systems), specifically in species such as cetaceans that use sound as a primary sensory modality. While most cetacean species produce context-specific sounds, little is known about the use of those sounds by potential conspecific eavesdroppers. We experimentally tested the hypothesis that a social cetacean, Risso's dolphin (Grampus griseus), is able to gather biologically relevant information by eavesdropping on conspecific sounds. We conducted playback experiments on free-ranging dolphins using three context-specific sounds stimuli and monitored their horizontal movement using visual or airborne focal follow observations. We broadcasted natural sequences of conspecific foraging sounds potentially providing an attractive dinner bell signal (n = 7), male social sounds simulating a risk of forthcoming agonistic interaction (n = 7) and female-calf social sounds representing no particularly threatening context (n = 7). We developed a quantitative movement response score and tested whether animals changed their direction of horizontal movement towards or away from the playback source. Dolphins approached the foraging and the social female-calf sounds whereas they avoided the social male sounds. Hence, by acoustically eavesdropping on conspecifics, dolphins can discriminate between social and behavioural contexts and anticipate potential threatening or beneficial situations. Eavesdropping and the ensuing classification of 'friend or foe' can thus shape intra-specific social interactions in cetaceans.

Risso's dolphins perform spin dives to target deep-dwelling prey

“…Tags were placed between the blowhole and dorsal fin, dorsally or on the flank. Foraging dives were filmed using an unpiloted aerial system (DJI Phantom 4 Pro) to record the movement behaviour of animals at the surface [ 18 ]. The onset of a spin dive is an active surface behaviour (near-surface acceleration plus rotation, inducing a marked trail of white water) that can be reliably characterized from visual observations ( figure 1 ; electronic supplementary material, video S1, [ 16 ]).…”

Rise of the machines: Integrating technology with playback experiments to study cetacean social cognition in the wild

“…As with some of the earlier studies with temporarily restrained common bottlenose dolphins, the typical responses we may see to some playback types may be more subtle movement behaviour rather than a vocal response. Another recent study combined sound playback experiments with both drone technology and sound and movement tags to measure the response of wild Risso's dolphins to conspecific calls (Barluet de Beauchesne et al, 2021). Here, different groups were exposed to either foraging sounds, male social sounds or female‐calf social sounds, and a quantitative movement response score was measured from the horizontal path of the focal group either using a drone (height 20–30 m) or using visual tracking from the research vessel.…”

“…Here, different groups were exposed to either foraging sounds, male social sounds or female‐calf social sounds, and a quantitative movement response score was measured from the horizontal path of the focal group either using a drone (height 20–30 m) or using visual tracking from the research vessel. Even though not all focal groups contained a tagged individual, or were exposed to all three playback treatments, the focal groups showed an approach response to both foraging sounds and female‐calf social sounds and a strong avoidance response to male social sounds (Barluet de Beauchesne et al, 2021). Together, these case studies demonstrate that both drones and biologging tags have started to facilitate field‐based playback experiments enabling us to gain new insight into how cetaceans perceive their social world.…”

“…Ideally, a within‐subject experimental design with individuals exposed to both treatment and control playbacks should be utilized, as this design offers significantly more power for the smaller sample sizes that are common when conducting playbacks to wild cetaceans (e.g. Barluet de Beauchesne et al, 2021; Cure et al, 2012; Curé et al, 2015; Deecke, 2007; King & Janik, 2013; Miller et al, 2012). Researchers should also strive to make their playback signals as realistic as possible, as any deviation from realism would likely introduce uninterpretable noise into any behavioural responses.…”

“…While tags allow for the tracking of one individual for an extended period of time, drones can track both a focal individual concurrently with nearby group members within the camera field‐of‐view (Barluet de Beauchesne et al, 2021; Durban et al, 2022; King et al, 2021; Ortiz et al, 2021). This can be especially valuable when evaluating responses to perceived agonistic signals or to potential predators.…”