Colobus chorus
In an intriguing and difficult investigation by Anne Schel and Klaus Zuberbuhler, communication in animals reports a dawn chorus from insect, amphibian and bird. The primate repertoire also includes a symphony of sounds for territorial and other display, especially in dense forest where visual displays are unnoticeable. There is nothing more delightful than waking in South East Asian forests to the gibbon dawn chorus, but South America Howlers and African Colobus seem to compete more loudly.
Budongo Field Centre in western Uganda is funded by the Royal zoological Society of Scotland and was the base for the study. Funding was provided by the EC and many other helpful sources aided and abetted its publication. The African black-and-white colobus (Colobus gureza) is the example drawn by Schel and Zuberbuhler, where rapid transmission across the jungle is a norm in good conditions. Sometimes, as when it's cold and wet, there is no display or only isolated events.
The authors refer to European robins responding better to strangers' calls and Campbell's monkeys responding only to older individuals. This has indicated that certain individual calls create response and not others in these species. Colobus have that common adolescent male problem where trouble is often caused to resident males by the "boy bands" or individuals. Distinctness of call could imply size of specimen or location of his group, helping a male to decide on response.
Hey, Anne, it's cold and it's wet. Don't call me: I'll call you! Black and White Colobus at the Bigodi Wetlands in Uganda via Shutterstock
The experimentation involved playback to determine any call individuality. A full chorusing was decided to be involvement of two or more groups in the low frequncy roaring sequnce that the typically produce. After huge difficulties in eliciting any response, a lengthier playback at the moment that chorusing was beginning produced the desired effect.
Interestingly, the males took little or no notice of caller ID. It's possible that with distances greater than 50m involved, perceiving sound qualities was difficult in an environment that was becoming noisy with other calls. Nonetheless, they began calling with gusto if other calls were heard with the correct scenario. Ugandan studies indicate fighting ability is highly correlated with the duration calling. Great tits are given as an example of male dominance using song. In this study, the stats seemed to show body size was indeed related to call duration, backing up the other studies. The morning chorus was therefore defined as a competition, with the calls aimed at females or potential rival males. Perhaps a silent male would have his territory invaded if his lack of competitive edge were perceived.
Anne and Klaus finally took some pride in the fact that their carefully prepared audio-show appeared realistic to the monkeys because of their appropriate responses (they showed a shorter latency to call naturally after hearing artificial playback). They also managed to prove the relationship between cold orwet conditions and lack of colobus calls .
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