The humpback whale (Megaptera novaeangliae) is an endangered species of baleen whale found throughout the world. A subset of the Polynesian population of humpbacks that migrates to Southeast Alaska participates in the group foraging activity known as "bubble-net feeding." We applied social network analysis to eight years of observations of co-occurrence to understand the social organization of bubble-net feeding whales. Results indicate that there are two large communities in Southeast Alaska that inhabit geographically distinct areas. Among social foraging humpbacks, there is a high degree of preference for affiliating with individuals from the same community. There are three types of whales in the communities: (1) "core" members who eat herring consistently, (2) intermittent members that were observed participating irregularly, and (3) one-season participators.
One of the specialized roles that some whales assume during bubble-net feeding is that of the whale who vocalizes to manipulate prey. We focused on the vocalizations produced by there task-specialists to see if we could classify distinct types of feeding calls. Classification and regression trees confirmed that most feeding calls were classifiable based on stable acoustic differences among the calls. The acoustic features that played the largest role in classifying calls were the mean and standard deviation of call formants, also known as harmonies. Formants are acoustic features that are stable within individual vocalizers. This indicates that the classification technique may provide a reliable method for identifying individual whales acoustically.
Humpback vocal behavior is integral to bubble-net feeding and could be affected by vessel noise during social foraging. We subjected feeding humpbacks to moderate levels of vessel noise from small boats. The humpbacks increased the length of spaces between individual vocalizations but did rot increase the overall length of vocal bouts. Contrary to expectations, the whales increased the diversity of vocalizations during vessel noise, instead of increasing redundancy. Channel capacity is an information theoretic measure that quantifies an environment's ability to carry communication based on noise present. We quantified the whales' response to sound by measuring a reduction in vocal rate as channel capacity decreased.
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 70/06, Dissertation Abstracts International|
|Subjects:||Ecology, Biological oceanography, Acoustics|
|Keywords:||Anthropogenic noise, Humpback whales, Megaptera novaeangliae, Social foraging|
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