Independent acoustic variation of the higher- and lower-frequency components of biphonic calls can facilitate call recognition and social affiliation in killer whales

Abstract

Each resident-type (R-type) killer whale pod has a set of stereotyped calls that are culturally transmitted from mother to offspring. The functions of particular call types are not yet clearly understood, but it is believed that calls with two independently modulated frequency components (biphonic calls) play an important role in pod communication and cohesion at long ranges. In this study we examined the possible functions of biphonic calls in R-type killer whales. First, we tested the hypothesis that the additional component enhances the potential of a call to identify the family affiliation. We found that the similarity patterns of the lowerand higher frequency components across the families were largely unrelated. Calls were classified more accurately to their respective family when both lower-and higher-frequency components were considered. Second, we tested the long-range detectability of the lowerand higher-frequency components. After adjusting the received levels by the killer whale hearing sensitivity to different frequency ranges, the sensation level of the higher-frequency component was higher than the amplitude of the lower-frequency component. Our results suggest that the higher-frequency component of killer whale biphonic calls varies independently of the lower-frequency component, which enhances the efficiency of these calls as family markers. The acoustic variation of the higher-frequency component allows the recognition of family identity of a caller even if the shape of the lower-frequency component accidentally becomes similar in unrelated families. The higher-frequency component can also facilitate family recognition when the lower-frequency component is masked by low-frequency noise.

Acoustic structure and information content of trumpets in female Asian elephants (Elephas maximus)

“…In the future, this calls for playback experiments to clarify if and how well Asian elephants are able to recognize and distinguish familiar conspecifics based on their trumpet vocalization. NLP may enhance individual acoustic distinctiveness in mammals [52,53,62]. Our results…”

“…In the future, this calls for playback experiments to clarify if and how well Asian elephants are able to recognize and distinguish familiar conspecifics based on their trumpet vocalization. NLP may enhance individual acoustic distinctiveness in mammals [ 52 , 53 , 62 ]. Our results indicate that this might be the case in the trumpets of adult Asian elephants, since the occurrence of the NLP types varies clearly between the individuals in this study ( Table 6 ).…”

“…Non-linear phenomena (NLP) typically occur in self-oscillating systems when driven to the limit or where multiple oscillators interact [ 51 ]. They are an integral part of mammal vocalizations and have indeed been suggested to facilitate individual recognition [ 52 , 53 ]. While some acoustic cues (e.g.…”

A novel theory of Asian elephant high-frequency squeak production

“…From a functional perspective, our findings on acoustic structure and on alarming and arousing call contexts are congruent with prevalent theories of high-frequency, modulated, chaotic, and repetitive calls to signal fearful, appeasing, or conflicting motivation [ 71 ], affect, or general arousal [ 72 ] over relatively close distances [ 73 ]. NLP and the potential for biphonation from two sources, such as the squeak-snort we described, may enhance the squeaks’ unpredictability and help hinder the receiver’s habituation [ 65 , 74 ] as well as boost individual acoustic distinctiveness [ 10 , 65 , 75 – 77 ]. Individual recognition may facilitate ranging, i.e., allowing the receiver to infer the sender’s distance based on the degradation of acoustic parameters [ 78 ] in dense habitats with low visibility.…”

Passive acoustic monitoring of killer whales (Orcinus orca) reveals year-round distribution and residency patterns in the Gulf of Alaska

“…Clicks are used primarily for echolocation, especially while foraging 25,26 . Pulsed calls have high pulse-repetition rates that result in tonal sounds rich with harmonic structure, and are thought to be used for behavioral coordination and group recognition 25,[27][28][29][30] . Whistles are tonal sounds with minimal harmonic structure and have been documented primarily when animals are socializing in close proximity 25,31,32 .Resident, transient, and offshore killer whales all utilize these three vocalization types, but differ in aspects of their vocal behavior.…”