Adult female-calf acoustic communication signals in migrating east Australian humpback whales

Humpback whale (Megaptera novaeangliae) calf survival during migration is dependent upon them maintaining contact with their mothers, and acoustics likely plays a significant role in this. Here, we analysed calls (n = 255) produced by migrating humpback whale adult female-calf pairs (n = 15) off the east coast of Australia. First, we identified nine common call types that were then quantitatively separated into two distinct clusters. One cluster contained calls that were considerably longer in duration, lower in frequency, and narrower in bandwidth than those in the second cluster. These are proposed to have been produced by the adult females and calves, respectively. We then compared acoustic features within presumed age class. Minimum, peak, and maximum frequencies were significantly different across both adult females and calves (Kruskal-Wallis, p < 0.05), suggesting that their calls encode socially relevant information regarding physical signaller attributes (i.e. age and body size). This study established a baseline adult female-calf call repertoire produced during the migration of east Australian humpback whales. Potential vocal masking from anthropogenic noise is of particular concern for communications between adult females and their calves, as it may put calves at risk of becoming separated from their mothers.