Acoustic characteristics of humpback whale (Megaptera novaeangliae) mother and calf vocalizations in the Hawaiian wintering grounds

Abstract

Humpback whale calves in the winter breeding grounds vocalize and the spectral characteristics of some of these vocalizations have been described, but sound levels of calf vocalizations have not been investigated. There is also a lack of general information on vocalizations from mothers. To address these issues, we deployed suction cup acoustic and movement recording tags on humpback whale calves, mothers and a lone post-yearling stage female on the Hawaiian breeding grounds to record vocalizations and percussive sounds. Deployments took place in waters off West Maui over four winter seasons. Tags were deployed on 7 humpback whale mothers, 6 calves, and one lone female for approximately 57 hours of recordings. Calling rates of tagged animals were relatively low compared to song, with individual’s means ranging from 0 to 16 vocalizations per hour. However, most calls occurred singly or in bouts, with long periods of silence before the next vocalization or set of vocalizations. These included sounds resembling non-calf social sounds as well as single song units, with durations up to 2 seconds and fundamental frequencies below 1.5 kHz. Our findings provide information that is critical to understanding vocal development in humpback whale calves and the sounds produced by adult females.