Characterization of fin whale song off the Western Antarctic Peninsula

Abstract

Song is produced by a variety of terrestrial and marine animals and is particularly common among baleen whales. Fin whale (Balaenoptera physalus) song is comprised of relatively simple 20 Hz pulses produced at regular intervals. The timing of these intervals, in addition to the presence and frequency of overtones, appears to be unique to each population. The purpose of this study was to characterize Western Antarctic Peninsula fin whale song and describe temporal pattern variations in song type and occurrence. Recordings were collected in the area from 2001–2004 and again 2014–2016. One song type was identified with a primary inter-pulse interval (IPI) of approximately 14 s and secondary IPI of 12.5 s. This song occurred in three pattern variants: singlet, doublet, and long triplet. The interval between pulses increased by 1.5 s between recording periods while the frequency of the overtones decreased from 89 Hz to 86 Hz. Song was never recorded in August and while it was recorded at other times in some years, it was consistently present in recordings from April through June across all years. While multiple pattern variants were present each year, singlets were generally the most prevalent variant. Doublets and triplets occurred from February through June, with highest levels of variants in February. In later years the triplet variant presence increased and in 2016 it comprised 53% of recorded song bouts. Further research is needed to understand the reasons why song changes over time and to examine the feasibility of using song to delineate and identify populations.

Temporal evolution of the Mediterranean fin whale song

“…Atlantic – 0.5 s/year – + 5.5 s Watkins et al 5 N.W. Atlantic – – – + 6 s Furumaki et al 46 Chukchi Sea – 0.5 s/year – + 1 s Širović et al 24 Gulf of California – 1 s/year – + 8 s Wood and Širović 20 W. Antarctic − 0.2 Hz/year 0.1 s/year – – Ours Mediterranean – 0.1 s/year –0.1 Hz/month – …”

“…As for the IPI shift slopes, differences across populations shown in Table 2 might arise culturally 9 , 10 , 20 . The cultural hypothesis holds if a phenomenon is shown to be learned and taught by peers, not genetically determined, and not triggered solely by environmental factors 47 .…”

“…These two categories are sometimes labelled classic 20 Hz pulse and back-beat, we will refer to them as type A and B for short (A being the higher pitched pulse). Fin whales of the Pacific and Atlantic often exhibit sequences that alternate between two stereotypical IPIs 9 , 10 , 20 . These are called doublet patterns, as opposed to singlets where only one IPI occurs.…”

“…Besides geographical variations, fin whale song structures also exhibit temporal variations, such as seasonal IPI increases 5 , 11 , 21 , and inter-annual variations of IPI and peak frequency 9 , 10 , 20 , 24 . Seasonal IPI increases appear to be synchronised with mating cycles, suggesting a link between the two (increasing testes activity or decreasing competition 21 ).…”

“…This highlights the importance of considering the song’s function in the interpretation of temporal patterns 25 . On the other hand, the drives for inter-annual trends remain unclear, with some emerging hypothesis for a cultural phenomenon 9 , 10 , 20 . Besides, with the observation of synchronous inter-annual shifts of both IPI and center frequencies in Pacific fin whale songs, the hypothesis of a link between the two arises.…”