Evidence for discrimination between feeding sounds of familiar fish and unfamiliar mammal-eating killer whale ecotypes by long-finned pilot whales

Abstract

Killer whales (KW) may be predators or competitors of other cetaceans. Since their foraging behavior and acoustics differ among populations ('ecotypes'), we hypothesized that other cetaceans can eavesdrop on KW sounds and adjust their behavior according to the KW ecotype.We performed playback experiments on long-finned pilot whales (Globicephala melas) in Norway using familiar fish-eating KW sounds (fKW) simulating a sympatric population that might compete for foraging areas, unfamiliar mammal-eating KW sounds (mKW) simulating a potential predator threat, and two control sounds. We assessed behavioral responses using animal-borne multi-sensor tags and surface visual observations. Pilot whales barely changed behavior to a broadband noise (CTRL-) whereas they were attracted and exhibited spyhops to fKW, mKW and to a repeated-tonal upsweep signal (CTRL+). Whales never stopped nor started feeding in response to fKW whereas they reduced or stopped foraging to mKW and CTRL+.Moreover, pilot whales joined other subgroups in response to fKW and CTRL+ whereas they tightened individual spacing within group and reduced time at surface in response to mKW.Typical active intimidation behavior displayed to fKW might be an anti-predator strategy to a known low-risk ecotype or alternatively a way of securing the habitat exploited by a heterospecific sympatric population. Cessation of feeding and more cohesive approach to mKW playbacks might reflect an anti-predator behavior towards an unknown KW ecotype of potentially higher risk. We conclude that pilot whales are able to acoustically discriminate between familiar and unfamiliar KW ecotypes, enabling them to adjust their behavior according to the perceived disturbance type.

Severity Scoring of Behavioral Responses of Sperm Whales (Physeter macrocephalus) to Novel Continuous versus Conventional Pulsed Active Sonar

“…Killer whales present in the area are mostly fish-eating killer whales which might not represent a predator threat for sperm whales. Sperm whales may be able to discriminate acoustically between mammal-eating and fish-eating killer whales as has been shown in other marine mammal species (pinnipeds: [50]; cetaceans: [43,51]). If not perceived as a risk of predation, the presence of blackfish species might still represent a type of threat associated to the competing interest with sympatric species to exploit of the same habitat [43].…”

“…Sperm whales may be able to discriminate acoustically between mammal-eating and fish-eating killer whales as has been shown in other marine mammal species (pinnipeds: [50]; cetaceans: [43,51]). If not perceived as a risk of predation, the presence of blackfish species might still represent a type of threat associated to the competing interest with sympatric species to exploit of the same habitat [43]. Moreover, it could be that both blackfish species, i.e., pilot whales and killer whales, that we were not always able to distinguish, lead to different behavioral responses and that they influenced the response to sonar differently.…”

“…Such apparent tolerance to sonar could lead to underestimation of responses in a population living in a more pristine habitat devoid of naval sonar exercises. Novelty has been indeed suggested to potentially influence the probability of responses in marine mammals [42], including cetacean species (e.g., long-finned pilot whales [43] and bottlenose whale [15]).…”

“…Heterospecific context could have potential influence on cetacean responsiveness to anthropogenic disturbance such as sonar. The detection of potential predatory killer whales triggers consistent and clear behavioral responses in many cetacean species including sperm whales [37,43,49]. Given blackfish species might represent potential threatening stimulus for sperm whales, we thus suspected that their presence could influence the whales' behavior and responses to sonar.…”

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

“…Eavesdropping in cetaceans has been poorly studied, relatively to terrestrial animals. Most studies focussed on heterospecific cetacean dyads, especially predator-prey systems, demonstrating the importance of sound eavesdropping in the mediation of interspecific interactions (Fish and Vania 1971;Cummings and Thompson 1971;Tyack et al 2011;Curé et al 2013Curé et al , 2015Curé et al , 2019Bowers et al 2018;Benti et al 2021). Regarding the acousticallymediated interactions within species, some pioneering studies using playbacks on cetacean species were conducted in the humpback whale (Tyack 1981(Tyack , 1983Mobley et al 1988), the right whale (Clark and Clark 1980;Parks 2003) and the killer whales (Filatova et al 2011) and showed that the detection of conspecific sounds could trigger behavioural responses.…”