Humpback whale adult females and calves balance acoustic contact with vocal crypsis during periods of increased separation

• Published in: Ecology and evolution Vol. 12; no. 2; pp. e8604 - n/a
• Main Authors: Indeck, Katherine L., Noad, Michael J., Dunlop, Rebecca A.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.02.2022; John Wiley and Sons Inc; Wiley
• Subjects: acoustic crypsis; Acoustics; active space; Aquatic mammals; behavioral states; Behavioural Ecology; Calves; communication strategy; Conspecifics; contact calling; Crypsis; Data collection; Depth perception; Families & family life; Females; humpback whales; Noise; parent–offspring interaction; Risk reduction; Separation; Whales & whaling; active space; parent–offspring interaction; behavioral states; humpback whales; separation; communication strategy; acoustic crypsis; contact calling
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.8604

Acoustic communication is important for animals with dependent young, particularly when they are spatially separated. Maternal humpback whales (Megaptera novaeangliae) use acoustic calling to help minimize the risk of separation from their young calves during migration. These pairs also use acoustic crypsis to minimize detection by males. How they balance a restricted active space with the need to maintain acoustic contact during periods of separation is not yet understood. Here, we analyzed movement metrics of tagged adult female–calf pairs during migration to identify two behavioral states, “resting/milling” and “travelling.” When travelling, these pairs dived synchronously and exhibited little to no spatial separation. Alternatively, adult females had significantly longer dive durations (p < .01) when resting, and while they spent prolonged times at depth, calves would surface several times independently. This demonstrated that these pairs are frequently separated during periods of rest. We then determined whether the call rates and acoustic levels of these pairs increased with more frequent separation, finding that both adult females and calves significantly increased their call rates, but not levels, when resting. We also found that adult female–calf pairs have a restricted active space, with less than 15% of calls estimated to be detectable beyond 2 km. However, as with call level, detection distance did not differ significantly between the two behavioral states. In summary, adult female–calf pairs maintain successful communication during periods of separation by calling more frequently rather than by producing louder calls. This strategy aids in maintaining acoustic contact while simultaneously limiting detectability by conspecifics. Maternal humpback whales (Megaptera novaeangliae) must balance acoustic calling to help minimize the risk of separation from their young calves during migration, with acoustic crypsis to minimize detection by males. We found that adult female–calf pairs maintain successful communication during periods of separation by calling more frequently rather than by producing louder calls. This strategy aids in maintaining acoustic contact while simultaneously limiting detectability by conspecifics.