Western North Atlantic humpback whale fall and spring acoustic repertoire: Insight into onset and cessation of singing behavior

Abstract

Humpback whale songs have been described worldwide and studies exploring non-song vocal behavior continue to expand; however, studies on the transition periods when whales shift to and from the seasonal behavioral state of singing are lacking and may be potentially informative regarding the proximal factors controlling the onset and offset of humpback whale male singing. Acoustic recorders collected data off eastern Canada continuously from the Bay of Fundy in the fall of 2015 and near-continuously off northeast Nova Scotia in the spring of 2016. Humpback whale acoustic occurrence and behavior were identified by systematically reviewing a subset of acoustic recordings for presence before analyzing the highest quality recordings for behavior. The onset of singing in the fall was gradual over a period of about three weeks with an intermediate form, termed “song fragment,” occurring prior to full songs. In comparison, singing in the spring seemed to end abruptly with few song fragments. Song fragments could be produced by juveniles learning to sing for the first time or mature males preparing for breeding activities prior to migrating to southern breeding grounds. The authors propose an alternative hypothesis that the timing and manner of transitions could be driven by physiological processes similar to those documented in songbirds.

Contribution to unravel variability in bowhead whale songs and better understand its ecological significance

“…Directly linked to unit repetition, variability across renditions of the same song have been previously reported including variability in song duration along a song bout 2 and the occurrence of 'primitive versions' during the initial development of a song as well as song variants based on unit or phrase repetition, order or absence 3,8 . Similar variants have been recently identified as "song fragments" in humpback whales songs 20 . Collectively, the bowhead whale acoustic studies indicate that variability at multiples levels is an important part of the bowhead whale singing behaviour.…”

Where, when, and why do western North Atlantic humpback whales begin to sing?

“…While the ultimate reason for singing is successful reproduction, several proximate functions have been proposed, including to attract females (Winn and Winn 1978;Tyack 1981), stimulate receptivity in females (Smith et al 2008), form male coalitions (Darling et al 2006), establish dominance (Darling and Bérubé 2001), and/or mediate competitive interactions between males as part of a lek mating system (Cholewiak et al 2018). Male song is predominant on warm water breeding grounds, but it also occurs during migration and on the feeding grounds pre and post migration (Mattila et al 1987;McSweeney et al 1989;Magnúsdóttir et al 2014;Kowarski et al 2018Kowarski et al , 2019. There is some evidence that humpback whales occur at high latitudes throughout the year, suggesting that perhaps not all individuals migrate, or perhaps that not all individuals migrate at the same time (Pomilla et al 2014).…”

“…In the western Atlantic a population of humpback whales, thought to be distinct from their eastern Atlantic counterparts (Stevick et al 2006), migrate between their summer feeding grounds that include the waters off eastern Canada and the USA and their winter breeding grounds of the Caribbean (Whitehead and Moore 1982;Martin et al 1984;Katona and Beard 1990;Palsbøll et al 1997;Smith et al 1999;Jann et al 2003). In the fall and winter, humpback whale songs have been recorded on known western North Atlantic feeding grounds including the Bay of Fundy, Canada, and the Stellwagen Bank National Marine Sanctuary, USA, as well as in the offshore Gully submarine canyon and eastern Scotian Slope of Nova Scotia (Vu et al 2012;Stanistreet et al 2013;Kowarski et al 2018Kowarski et al , 2019. Kowarski et al (2019) described the period of song onset in the fall in the Bay of Fundy and defined two categories of singing.…”

“…In the fall and winter, humpback whale songs have been recorded on known western North Atlantic feeding grounds including the Bay of Fundy, Canada, and the Stellwagen Bank National Marine Sanctuary, USA, as well as in the offshore Gully submarine canyon and eastern Scotian Slope of Nova Scotia (Vu et al 2012;Stanistreet et al 2013;Kowarski et al 2018Kowarski et al , 2019. Kowarski et al (2019) described the period of song onset in the fall in the Bay of Fundy and defined two categories of singing. The first was 'song fragments' which occurred during the early months of song onset and ranged from one phrase or subphrase to two or more themes that are not repeated.…”

Acoustic communication of female-calf humpback whales during migration

“…Only males sing and it is believed that song plays an important role in reproduction, as it is primarily heard on the breeding grounds (Winn & Winn 1978;Tyack 1981). Nevertheless, recent studies have shown that, although occurring to a lower extent along the migration routes and on the feeding grounds, singing activity persists throughout the year (McSweeney et al 1989;Clapham & Mattila 1990;Charif, Clapham & Clark 2001;Vu et al 2012;Garland et al 2013;Kowarski et al 2019;Magnusdottir & Lim 2019). Despite the extensive effort put into the study of song, its exact function is still unknown, although the predominant hypothesis is that it functions as a sexual display and an indicator of fitness to females (Winn & Winn 1978;Tyack 1981;Smith et al 2008).…”