Abstract
Eavesdropping, the detection of communication signals by unintended receivers, can be beneficial in predator-prey interactions, competition, and cooperation. The cosmopolitan killer whaleOrcinus orcahas diverged into several ecotypes which exhibit specialised diets and different vocal behaviours. These ecotypes have diverse ecological relationships with other marine mammal species, and sound could be a reliable sensory modality for eavesdroppers to discriminate between ecotypes and thereby respond adaptively. Here, we tested whether humpback whalesMegaptera novaeangliaein the Northeast Atlantic responded differently to playback of the sounds of 2 killer whale ecotypes, Northeast Atlantic herring-feeding killer whales representing food competitors and Northeast Pacific mammal-eating killer whales simulating potential predators. We used animal-borne tags and surface visual observations to monitor the behaviour of humpback whales throughout the playback experiments. Humpback whales clearly approached the source of herring-feeding killer whale sounds (5 of 6 cases), suggesting a ‘dinner-bell’ attraction effect. Responses to mammal-eating killer whale sounds varied with the context of presentation: playback elicited strong avoidance responses by humpback whales in offshore waters during summer (7 of 8 cases), whereas the whales either approached (2 of 4 cases) or avoided (2 of 4 cases) the sound source in inshore waters during winter. These results indicate that humpback whales may be able to functionally discriminate between the sounds of different killer whale ecotypes. Acoustic discrimination of heterospecific sounds may be widespread among marine mammals, suggesting that marine mammals could rely on eavesdropping as a primary source of information to make decisions during heterospecific encounters.
Highlights
The ability to eavesdrop on acoustic signals, that is, the detection of communication signals by unintended receivers of the same or another species, can affect animal fitness (McGregor 1993)
Humpback whales approached the source of herring-feeding killer whales (HFKWs) sounds inshore during winter (5 of 6 experiments, Fig. 2), whereas they strongly avoided the source of mammal-eating killer whales (MEKWs) sounds offshore during summer (7 of 8 experiments, Fig. 2)
Our results indicate that the behavioural responses exhibited by humpback whales to the playback of killer whale sounds differed according to the combination of killer whale ecotype and ecological context of presentation
Summary
The ability to eavesdrop on acoustic signals, that is, the detection of communication signals by unintended receivers of the same or another species, can affect animal fitness (McGregor 1993). Mar Ecol Prog Ser 660: 217–232, 2021 able to detect and identify acoustic cues informing them about predator presence and to adopt appropriate behaviours to reduce the risk of predation such as avoidance (e.g. Cummings & Thompson 1971, Emmering & Schmidt 2011), stealth Rankin et al 2013), or mobbing (e.g. Curé et al 2012) Another way to reduce predation risk can be the detection and use of alarm calls released by other species within the prey community Predators may in turn improve their foraging efficiency by reducing the production of acoustic cues that can be used by prey to detect and avoid them The receiver’s environment may be important in shaping its responses, such as habitat topography (e.g. Perla & Slobodchikoff 2002, Kern et al 2017) or the size and composition of the receiver’s social group (e.g. LaGory 1987)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
