Page 50 - Summer2017

Marine Mammal Acoustic Behavior
Figure 3. Map of the South Pacific showing the humpback breeding grounds from which song was recorded by Garland et al. (2011).
compare song data recorded over a period of 11 yr (Garland et al., 2011). Figure 3 shows the locations of the six breeding grounds.
When the song data from the different breeding grounds were analyzed, song types were found to be shared across the full 6,000-km span from Eastern Australia to French Polyne- sia (Figure 4). However, the song was never the same across all sites during the same year. Rather, each song type (rep- resented by a color in Figure 4) originated in East Australia and then spread from west to east, taking 2-3 yr to reach French Polynesia. This process represents a particularly large scale for repeated cultural diffusion from a population where new material originated in east Australia to breeding grounds farther to the east.
Functions of Marine Mammal Calls
The first phase of marine mammal bioacoustics focused on which species made which sounds. This is still an active re- search question today, but by 1980, interest in marine mam- mal behavior broadened to also focus on the contexts in which animals make a call, how others respond, and how calls function in communication. In many whale and seal species, adult males repeat complex vocalizations, called songs, during the breeding season. In many seal species and some cetaceans such as the humpback whale discussed in the Song of Humpback Whales, males congregate during the breeding season in traditional areas where females come to mate. The complex songs males produce advertise their readiness to compete with other males and to mate with females. Female vocalizations also play a role in reproduc-
tion for some species. For example, female northern right whales produce a scream call that is thought to attract males (Parks and Tyack, 2005; http://www.dosits.org/files/ dosits/egscream.mp3).
Some seals breed on beaches where inter- actions can be observed relatively easily by terrestrial human observers; other species breed at sea where observations are more difficult. All seals can vocalize in air and un- der water, and in all species observed, vocal communication plays a role in breeding be- havior. Elephant seals are one of the species that mate on land; males use vocalizations to assess the fighting ability of other males, and females compare different males by listen-
Figure 4. Song types identified by Garland et al. (2011) in the South Pacific from 1998 to 2008. Each color represents a song type. If two colors are listed for 1 yr at one site, both song types were recorded during that year.
48 | Acoustics Today | Summer 2017