Tuesday, April 19, 2011

A Catchy Tune

image from the Daily Mail, story linked below, credit to Alamy
 I heard a song in the car earlier today and now it's stuck in my head. I've been silently, and sometimes no so silently, singing it all day. So imagine my surprise when I was flipping, or rather clicking, through the most recent issue of Current Biology and this study all about the cultural transmission of humpback whale song caught my eye.

Cultural transmission. Put simply it is the social learning of information or behaviors within members of a species. In the animal kingdom you can find it in several large groups including cetaceans (whales and dolphins), birds, and primates. It can happen in a couple of different ways. Cultural traits can be passed vertically from parents to their offspring. They can be passed obliquely from older nonrelated individuals to younger individuals. And they can also be passed horizontally between unrelated individuals close to or within the same generation. Kinda makes sense right? I mean, where did you get your information as you grew up and where do you get it now?

The study for today's post takes a look at male humpback whales (Megaptera novaeangliae). This species is wide ranging, living in polar and tropical waters all over the globe, and they are known to migrate between northern and southern latitudes with the climatic cycle usually for feeding and reproduction. Humpback whales live in groups and are protective but not thought to be territorial. Both males and females will vocalize, but males produce long, loud, and often complex songs that function in sexual selection. It is known that whales within a population will sing the same song which will slowly change over time. This study looks at the horizontal transmission of these songs over the ocean basin.

Before discussing a paper about whale songs it is probably goon to note that the sounds of a song are arranged in a nested hierarchy: "themes" contain a number of repeated "phrases" which consist of a string of individual "units." In this study, the researchers picked field locations that corresponded to the multiple migration routes and breeding grounds within the western and central South Pacific region (northeastern Australia, New Caledonia, Tonga, American Samoa, the Cook Islands, and French Polynesia). Over an 11 year period they recorded humpback whale songs mostly using hydrophones suspended from boats. Then they viewed the songs as spectrographs so that they could look at each unit in the song clearly and then transcribe it based on the visual and aural qualities of the sound. The recorded sounds were classified and analyzed, comparing the similarity of songs and grouping all songs of the same type or themes together. The identified song types were grouped into six different lineages with color: pink, black/gray, blue, red, yellow, and green. When a song had comnpletely evolved and the orignial themes were replaced they were renamed/recolored. This made it easier to track the movement, evolution, and splits in song type between populations.

The study points out that at any one time males within a population show a strong conformity to a single song type containing the same themes sung in the same order. The pattern of the song evolves from year to year but all singers maintain conformity. When analyzing the songs they found that four new songs originating in eastern Australia gradually spread eastwards so that within two years the whales in French Polynesia were singing the same song. That is pretty fast over a really large area. Considering that, during the breeding season (July-October), there are several breeding groups where interchange is uncommon, what is going on?  The direction of the song transmission may be the detail that answers this question. The songs appear to have changed and radiated consistently from west to east in a series of cultural waves. One possible explanation for this directionality is that the eastern Australian population is the largest in the region and so its influence on the other populations is greater than the influence of the other populations on it. Another explanation is the migration. Males from different populations encounter each other along shared migration routes where they hear and learn each other's songs. Previous studies have shown that the eastern Australian population songs rapidly change, within two or three months, and so migratory routes would not need to overlap extensively and minimal contact would be required for song learning.

Overall, this study is a wonderful example of cultural transmission over a vast geographic area. The rate of change and the vocal linkage between populations is pretty incredible. Now I just need go get my next cultural wave of information to get this song out of my head.

Read the article here:
Garland, Ellen C. et al. (2011) Dynamic horizonal cultural transmission of humpback whale on at the ocean basin scale. Current Biology: 21, 1-5. (DOI: 10.1016/j.cub.2011.03.019)
The article and supplementary content includes audio recordings.

Visit the Whalesong  Project: http://www.whalesong.net/index.php

After some searching I found that this article has been picked up by some major news outlets, particularly in Australia:
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