In spring 2018, TDI’s humpback whale research in Hawaiian waters focused on determining whether there is a correlation between the acoustic characteristics of the song of individual singers recorded off Maui and their body size and testosterone levels. With these data, we can examine the question: Does song act as a display between males, perhaps to advertise their fitness allowing them to avoid energetically costly fights when meeting in competition over a female?
Aside from human language, one of the most complex vocalizations in the animal kingdom is the song of male humpback whales. Comprised of a series of unique themes in a particular order that may be repeated for hours and are sometimes transmitted culturally across individuals, humpback whale song has intrigued people of all ages for decades. Although humpback whale song is produced primarily on the breeding grounds and is clearly an integral part of the humpback whale mating system, the exact functions of song are still a matter of debate. In part, this is because individual female humpbacks rarely approach individual male singers. Instead, if a singer has a visitor, it is most often another male. This raises a question about whether song acts at least in part as a display between males, perhaps to advertise their fitness and avoid energetically costly fights when the males meet in competitive groups vying for access to a female.
To examine this question, TDI researchers partnered with Dr. Marc Lammers, Research Coordinator of the Hawaiian Islands Humpback Whale National Marine Sanctuary, and Dr. Shannon Atkinson and graduate student Kelly Cates of University of Alaska Fairbanks. Our goals were to:
- locate individual singers and obtain a tail fluke identification photo to match to our archival catalog,
- record their song and offline measure the amplitude (loudness) and other acoustic characteristics of song units,
- measure their body length using our videogrammetric technique, and
- obtain a small skin and blubber biopsy sample from which testosterone concentration could be determined.
The process of successfully obtaining all streams of data requires a full team effort, and over a two week window, we gathered full data sets from 5 singers. These have been added to our previous data on 7 singers, with more singers to be recorded and measured in Spring 2019. Once we obtain a large enough sample size, we can answer the question of whether song characteristics provide important information on the fitness of an individual singer, which is critical to understanding of the function of humpback whale song in the mating system.
To learn more about the humpback whale song and its potential function, check out Dr. Herman’s seminal 2017 paper: “The multiple functions of male song within the humpback whale (Megaptera novaeangliae) mating system: review, evaluation, and synthesis.”