Allopatric humpback whales of differing generations share call types between foraging and wintering grounds

Abstract

Humpback whales (Megaptera novaeangliae) are a cosmopolitan baleen whale species with geographically isolated lineages. Despite last sharing an ancestor ~ 2–3 million years ago, Atlantic and Pacific foraging populations share five call types. Whether these call types are also shared between allopatric breeding and foraging populations is unclear, but would provide further evidence that some call types are ubiquitous and fixed. We investigated whether these five call types were present on a contemporary foraging ground (Newfoundland, 2015–2016) and a historic breeding ground (Hawaii, 1981–1982). Calls were classified using aural/visual (AV) characteristics; 16 relevant acoustic variables were measured and a Principal Component Analysis (PCA) was used to examine within-call and between-population variation. To assess whether between-population variation influenced classification, all 16 variables were included in classification and regression tree (CART) and random forest analyses (RF). All five call types were identified in both populations. Between-population variation in combined acoustic variables (PC1, PC2, PC3) was lower within call types than among call types, and high agreement between AV and quantitative classification (CART: 83% agreement; RF: 77% agreement) suggested that acoustic characteristics were more similar within than among call types. Findings indicate that these five call types are shared across allopatric populations, generations, and behavioural contexts.

Humpback whale call repertoire on a northeastern Newfoundland foraging ground

“…Also, as noted by previous repertoire studies (Dunlop et al, 2007; Fournet et al, 2015), whups appear similar to moans described by Thompson et al (1986). Although shared average parameters (i.e., peak frequency, start frequency, duration) of the five calls in the Newfoundland repertoire fall within similar ranges as these call types in other regions (see Table 3) and share similar visual characteristics on spectrograms, we cannot conclusively state that these call types are shared with other regions without direct, quantitative comparisons, as done in previous studies (e.g., Epp et al, 2021; Fournet et al, 2018c). For the same reasons, we cannot conclusively state whether the remaining eight call types described in this study are unique to the Newfoundland foraging grounds, or are simply variants of previously described calls.…”