Thursday, 26 November 2009

More social networking for pandas

Though olfaction is probably the most advanced of the panda’s senses, recent work on acoustic communication reveals just how important sounds are for successful social networking in a complex bamboo-based world.

A really thorough scrutiny of the acoustic structure of calls from individual pandas has just appeared in The Journal of the Acoustical Society of America and it shows them to be highly distinct. Furthermore, two particular features of a vocalization – its pitch and rapid variation in its volume – seem to be the factors that can best explain that distinctiveness. This computer-based analysis of panda acoustics also made a very interesting parting-shot. By comparing calls from related individuals, it appears as though certain acoustic features have a strongly heritable component. Vocal cues, suggested Ben Charlton and his co-workers in the abstract, “could be used as a measure of genetic relatedness.” I haven’t yet got to look at the entire paper, so I’m not sure whether they mean pandas, researchers or both might be using calls to assess relatedness.

OK, so there are fuzzy bits on graphs that humans can use to distinguish one panda from the next. But do pandas pay attention to these features of sound? In an experiment that mirrored one on olfaction carried out by Ronald Swaisgood and his colleagues more than a decade ago, Charlton and friends (including Swaisgood as a matter of fact) habituated female pandas at the Chengdu panda base to the recorded calls of a single male before switching to the bleats of another. The sudden increase in attentiveness on hearing the novel call demonstrates quite clearly that females are able to distinguish males on the basis of sound alone.

In a couple of follow-up experiments, the researchers manipulated aspects of the male vocalization to see what that did to females’ reactions. With the frequency normalized, females still perked up at the change from male A to male B but with volume variation under control they were not responsive to the switch. So volume variations seem crucial to the ability to distinguish between individuals. “Although giant panda bleats are low amplitude and features of amplitude modulation would be particularly susceptible to attenuation in the densely forested natural habitat that giant pandas inhabit…, these vocalizations could be used for close-range signalling of identity in direct encounters,” suggest Charlton and colleagues in Biology Letters.

A further paper, published in Animal Behaviour, revealed that there are clear differences in the bleats emitted by males and females, useful if you’re a solitary animal living in a dense bamboo forest. A male’s vocalization also appears to give an indication of his size and a female’s call appears to give away her age.

Next up. Panda vision.

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