Changes in humpback whale song structure and complexity reveal a rapid evolution on a feeding ground in Northern Norway

Abstract

Singing behaviour by male humpback whales (Megaptera novaeangliae) has traditionally been associated with low-latitude breeding grounds. However, in recent years, this vocal behaviour has been increasingly reported outside these areas. All singers in a given population sing the same version of a song and this song is continually evolving over time with modifications on different levels within the song structure. Tracing changes in whale song will help to undercover the drivers underlying this vocal display and contribute to the understanding of animal culture and its evolution. To determine the progressive changes in songs found on a subarctic feeding ground and migratory stopover, a detailed analysis of humpback whale song recordings from Northern Norway was conducted. Passive acoustic data from the Lofoten-Vesterålen Ocean Observatory (LoVe), collected using a bottom-moored underwater hydrophone, were used from January - April 2018 and January 2019. Two measures of the song structure were examined: (1) sequence similarities using the Levenshtein distance and (2) song complexity using a principal component analysis (PCA). In total, 21 distinct themes were identified which presented highly directional, structural changes over time. Two themes from 2018 reoccurred in 2019, whereas all other themes in 2019 appeared to be evolved versions of 2018 themes. All songs grouped into three general clusters, reflecting the rapid evolution over the study period. With all sampled animals singing the same version of the song, this might indicate that the singers are either from the same breeding population or that song learning occurred before the study period. Song complexity appeared to follow the trend of song progression; songs became more complex as they evolved over the months in 2018 and decreased in complexity between the years, returning to a more simplified song in 2019. The results confirm that humpback whale song exhibits a rapid progression on a shared subarctic feeding ground, with strong potential for song exchange and opportunities for cultural transmission between populations in the North Atlantic.

The migratory whale herd concept: A novel unit to conserve under the ecological paradigm

“…However, though singing was once thought to be largely confined to wintering grounds (Charif et al, 2001;Clapham & Mattila, 1990), we now know that humpback whales sing both on their feeding grounds late in the season and on migration (Clark & Clapham, 2004;Magnúsd ottir et al, 2014;Mattila et al, 1987;Noad & Cato, 2007;Norris et al, 1999;Schall et al, 2022;Stimpert et al, 2012;Tyarks et al, 2021;Vu et al, 2012), providing a mechanism for transmission of songs among winter areas in the absence of direct exchange of individuals between wintering grounds (Garland et al, 2013;Owen et al, 2019). Rapid annual shifts in humpback whale song, called song "revolutions," have been attributed to exposure to song from other populations, either on the feeding ground or migratory route (Garland et al, 2011(Garland et al, , 2013Owen et al, 2019;Tyarks et al, 2022) or due to the movement of a small number of males between wintering areas (Allen et al, 2018;Noad et al, 2000). Thus, though humpback song transmission is an active and intriguing area of research that may yet fundamentally alter our understanding of humpback whale behavior and learning, the data to date are consistent with the high site fidelity to migratory destinations implied by the migratory herd concept.…”

Seasonal acoustic presence of marine mammals at the South Orkney Islands, Scotia Sea

“…The vocal repertoire of a species can be determined by both sex and sexual maturity, and the degree of vocalization may vary between seasons [ 25 , 53 – 55 ]. For example, while humpback whales produce many different types of social calls, only male humpbacks are known to produce highly complex, long-lasting songs associated with breeding and migration [ 54 , 56 , 57 ]. By contrast, male blue whales and fin whales produce simple low-frequency calls [ 2 , 22 , 52 ].…”