| Summary: | Humpback whales, Megaptera novaeangliae, are migratory baleen whales that travel to the northern Pacific Ocean during the summer to feed on herring in preparation for their upcoming breeding season. Some of these whales perform a specialized social foraging behavior called bubble-net feeding, in which they coordinate the blowing of bubbles in a conical fashion around a school of fish, allowing group members to feed on the school. In addition, the whales produce a series of low frequency, high amplitude vocalizations known as food calls which are likely used to further herd their prey into tighter schools. These calls fall into two main categories, tonal and modulated. The lowest frequency component, known as the fundamental frequency, of tonal food calls is fairly constant, while the fundamental frequency of modulated food calls oscillates over time. During the production of some food call series, the caller’s voice may ‘crack’. Voice cracking is an abrupt change in the fundamental frequency that may be caused by stress in the vocal apparatus of the individual. We hypothesized that food call production causes strain on the vocal tract of individual whales, which can lead to voice cracking. From underwater recordings of humpback whales performing bubble-net feeding collected in the Gulf of Alaska, we compared food call sequences which contained voice cracks with those that did not. We expected voice cracking to occur more often as production difficulty increases. Call difficulty was assessed by measuring call duration, the number of calls in a series, and the type of food calls produced. For series containing voice cracks, we recorded when in the series the crack occurred. Based on our hypothesis, we expected vocal cracks to occur later in the series, in longer food call series, after food calls of longer duration, and during or after the production of modulated food calls.
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