Abstract
Mysticetes and odontocetes differ in many morphological and behavioral aspects related to feeding. Odontocetes echolocate using clicks to localize prey, while the mechanism through which mysticetes orient and find food is unknown. In this study, DTAGs were deployed on four humpback whales (Megaptera novaeangliae) observed feeding off the northeastern United States. From two of the four tagged whales, bouts of clicks produced with a temporal pattern resembling odontocete echolocation were recorded and 102 bouts of megapclicks were identified. Spectrally, megapclicks were unlike previously reported humpback sounds or odontocete clicks, and also had much lower amplitudes (peak frequency ∼1700 Hz, RL 148±6 dB Re: 1 uPa peak). Interclick intervals (ICI) were bimodally distributed (peaks at 25 and 80 ms), with shorter ICIs occurring at the end of megapclick bouts, in a pattern similar to an odontocete terminal buzz used in foraging. Behavioral sensor data supported a possible foraging function for megapclicks. All megapclick bouts occurred during nighttime hours, and the terminal buzz was associated with a sharp body roll of greater than 70 deg. Low source levels, among other characteristics, contraindicate an echolocation function; however, further analysis and research is required to distinguish among this and other hypotheses for sound function.
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