Monday, November 28, 2011

Guereza colobus monkeys sing chorus at dawn to 'show off'

Scientists have revealed some of the secrets of the loud, growling monkey dawn chorus in the forests of Uganda.

Guereza colobus monkeys appear to join the chorus to advertise their size and dominance.

The scientists managed, for the first time, to trigger a forest-wide chorus using a recording.

They reported their lastest insight into this early morning "wall of sound" in the journal Behavioural Ecology and Sociobiology.

Anne Marijke Schel carried out the work at Budongo Conservation Field Station, Uganda, as part of her PhD project.

She and her colleague, Prof Klaus Zuberbuhler from the University of St Andrews, Scotland, wanted to find out why the monkeys took part in what they described as a "vocal spectacle".

"The behaviour usually starts before dawn by one individual calling somewhere in the forest," said Dr Zuberbuhler.

"Typically, this is contagious so that his calling spreads first to neighbouring groups, until a large part of the forest is covered by calling monkeys."

The scientists recorded the dawn chorus and used playback experiments to see if they could trigger one of a forest-wide calls to find out more about why the animals joined in.

Dr Schel explained: "It took a while, but we eventually found out that we could trigger a chorus if we played the recording continuously [for] about 60 seconds.

"This was much faster than if the chorus started naturally."

Several species of monkey perform a dawn choruses, including howler monkeys, which appear to claim their territory by calling

Gibbons are notoriously vocal in the morning. Pairs sing loud duets that are thought to repel intruders and advertise their pair bond.

Dr Schel's studies also revealed that the call of relatively diminutive males would always elicit a response.

"We think it's the case that if someone very small calls, you counter-call to show off that you're bigger and more dominant," she explained.

Dr Reinmar Hager, an evolutionary biologist from the University of Manchester explained that dawn chorusing, which most people associate with the early morning twittering of songbirds, actually plays an important role in primate society, especially male-male competition and territoriality.

He added that understanding its role would help us understand primate social systems.

"Knowledge of this is crucial for species preservation and [understanding] the habitat they require," he said.

"[Research into] vocal communication in non-human primates will [also] help us understand the role of more sophisticated communication patterns in human interactions and why they may have evolved.
"After all, our ancestors were non-speaking apes and our language presumably evolved from such acoustic signals.

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