Fin whale singing decreases with increased swimming speed.

Christopher W Clark,George J Gagnon,Adam S Frankel

doi:10.1098/rsos.180525

Abstract

The attributes of male acoustic advertisement displays are often related to a performer's age, breeding condition and motivation, but these relationships are particularly difficult to study in free-ranging marine mammals. For fin whale singers, we examined the relationships between a singer's swimming speed, song duration and amount of singing. We used a unique set of fin whale singing and swimming data collected in support of the US Navy's marine mammal monitoring programme associated with the Navy's Integrated Undersea Surveillance System. A goal of the programme is to improve understanding of the potential effects of anthropogenic sound sources on baleen whale behaviours and populations. We found that as whales swam faster, some continued to sing, while others did not. If swimming speed is an indication of male stamina, then singing while swimming faster could be a display by which females and/or other males assess a singer's physical fitness and potential reproductive quality. Results have implications for interpreting fin whale singing behaviour and the possible influences of anthropogenic sounds on fin whale mating strategies and breeding success.

Highlights

Acoustic displays are subject to strong selection pressure when the level of display performance is related to signaller condition
The mean duty-cycle, including all non-singing periods, was 54.3% (s.d. 1⁄4 21.9, median 1⁄4 53.7, range 1⁄4 9.2–95.0), and the mean track swimming speed was 6.7 km h21 (s.d. 1⁄4 3.4, median 1⁄4 6.2, range 1⁄4 1.1–16.8). Based on this mean of track swimming speeds, and rounding that result to the nearest integer, we use 7 km h21 as the swimming speed at which we differentiate between swimmers that swam slower while singing and swimmers that swam faster while singing, while recognizing that this distinction is somewhat subjective and must not be used to overinterpret our results
57% of all singers started their tracks swimming at less than 7 km h21, only 31% of all singers continued swimming at less than 7 km h21 for their entire singing bout(s), while 69% of all singers swam at speeds greater than or equal to 7 km h21 during some period of their track

Summary

Introduction

Acoustic displays are subject to strong selection pressure when the level of display performance is related to signaller condition. Anurans and mammals, conspicuous features of male acoustic displays can provide reliable cues of male attributes attractive to females and threatening to rival males, and there are known trade-offs between conspicuous acoustic features and other male traits [1 –5]. For example, minimum formant frequency is negatively correlated with an index of breeding success and an honest indication of male body size and fitness, and a salient feature by which females and. For free-ranging cetaceans, there are no established methods by 2 which to experimentally determine whether or not an acoustic performance attribute (e.g. amount of sound production, consistency, duration, frequency range) can be linked to reproductive success, we assume that insights into possible performance attributes can be deduced from empirical observations

Methods

Results

Discussion

Conclusion