Same Ocean, Different Songs
February 2, 2012
Just because you've heard one whale song doesn't mean you've heard them all. A recent study proves that humpback whales on both sides of the southern Indian Ocean are singing different tunes. It's an unusual finding, contradicting previous evidence that showed humpbacks in the same ocean basin all croon a very similar song.
Generally, when whale researchers compare song from populations in the same ocean basins, they find the tunes contain similar parts or "themes." The differences in song between the Indian Ocean humpback populations most likely indicate a limited exchange between the two regions. The findings may also shed new light on how whale culture spreads.
The study, conducted by researchers from WCS, Columbia University, and Australia, appears in the January edition of Marine Mammal Science. Lead author Anita Murray conducted the research while a graduate student at Columbia University and WCS and is currently pursuing her doctorate at the University of Queensland in Australia.
"In the Northern Hemisphere, within an ocean basin whales sing songs that are composed of the same themes," she said. "However, whales in the southern Indian Ocean are singing almost completely different songs. Songs from Madagascar and Western Australia only shared one similar theme, the rest of the themes were completely different. The reason for this anomaly remains a mystery. It could be the influence of singing whales from other ocean basins, such as the South Pacific or Atlantic, indicating an exchange of individuals between oceans, which is unique to the Southern Hemisphere."
For the most part, it is the male humpback whales that sing as they court mates on their winter breeding grounds, or along their migratory routes and on summer feeding grounds. The songs are complex arrangements of parts or "themes," consisting of ascending and descending wails, moans, and shrieks repeated in cycles lasting up to 30 minutes. The transmission of songs between individuals from different populations is likely to occur on feeding grounds or during migration when whale populations mix. Alternatively, song transmission may occur when individual male "troubadours" travel to different breeding grounds between mating seasons or possibly during the same season.
The research team recorded humpback whale songs in two locations in coastal Madagascar and three locations along Western Australia during the 2006 breeding season. Research teams in both regions used hydrophones to record the songs of 19 individual whales. Overall, the authors captured more than 20 hours of whole and partial songs for visual and audio analysis. The comparison revealed few similarities between songs; of the 11 themes recorded in both regions, only one was shared by the two populations.
Due to the limited timeframe of the study, which occurred over a single breeding season, researchers say that they'll need to further analyze songs in Madagascar and Australia to examine the reasons for the differences in repertoire.
According to WCS conservationist Salvatore Cerchio, "Continued monitoring of these songs can provide us with valuable information on how whale songs are exchanged and how those channels of cultural transmission can be protected in the future."
WCS has been involved in research on humpback whales since the 1960s, when researchers from the New York Zoological Society (now WCS) discovered that the vocalizations of humpback whales are, in fact, songs, defined as a series of themes repeated in cycles. For the past decade, WCS's Ocean Giants Program has conducted an extensive molecular analysis of humpback whale populations in the southern Atlantic and Indian oceans in an attempt to better define discrete populations.
To learn more, read the press release.