I am currently doing a research about age-related alarm call duration, syllables/pulses, and fundamental frequency on Macaca fascicularis upon predator presence. Physiologically, I find the reason why more mature individuals produce longer alarm call duration, but I can not find the reason why it has to be longer. Duration length also relates with how many syllables or pulses they emit. So, is there any theory that suggests the longer call duration and more syllables or pulses they produce, the more information a call contains? If so, could you please let me know which articles support it? I have been trying to find the answer, but still can not find it.
Thank you so much
This is a fascinating question, I’m afraid I’m not aware of any research in this area, but a couple of things immediately struck me.
Perhaps the duration of the call has more to do with redundancy than information content. i.e. the call is repeated or lengthened to increase the chance that it will be heard (information received). It would be interesting to see if there was a correlation between call duration, or redundancy, and the likelihood that it will be heard. So if the intended recipients of the call were further away, or the environment/landscape made it more difficult for the message to be reach them, dense forest, etc.?
I would imagine giving an alarm call in the presence of a predator is a risky thing to do, you are immediately giving your location away. Perhaps the older macaques are more likely to put themselves at risk than younger ones? This could be analogous to some social insects. In some ant colonies older ants will undertake the more “risky” activities as their loss would have a smaller impact on the success of the colony than the loss of younger ants. A social group of macaques is very different to a colony of leaf cutter ants, but again, it would be interesting to see if there was a correlation between the net present value, in terms of adding to the future success of the troop, of an individual, and the risk taking behaviours such as the duration of the alarm call?
Perhaps the macaques are less altruistic, and the older ones have more experience or skill in evading the predator, so are able to minimise the risk associated with giving a longer alarm call.
Oh, I see, instead of the information contained in an alarm call, it might be because of redundancy. It makes sense though. But, I have ever read an article by Hollen & Redford (2009) that said the alarm call emitted by juveniles might contain wrong information or less specific information than one emitted by adults. So, I thought that maybe longer alarm call could contain more information than shorter one. Thank you very much for your answers.
http://www.sciencedirect.com/science/article/pii/S0003347209003479
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