Animals benefit from the sloppy eating behavior of monkeys

Forest animals often benefit from the sloppy eating behavior of monkeys, according to a new study from the University of Copenhagen. The researchers found that animals eavesdrop on monkeys while they are eating in hopes of snatching up discarded food.

“Monkeys are messy eaters. After just a few bites of a fruit, they let it fall to the ground. Other species benefit from this habit. But to do so most effectively, they need to know where and when the monkeys are eating. Here, our study demonstrates that mammals use eavesdropping,” said study lead author, Linnea W. Havmøller.

The team spent nine months in a rainforest in Panama studying how various types of fruit-eating animals, including coatis and agoutis, listen to capuchin and spider monkeys as they eat in the trees. 

When the half-eaten fruit often falls to forest floor below, the researchers discovered that animals are ready to pounce the moment they hear the food hit the ground.

“It is clear that, when terrestrial animals hear monkeys in a tree, they head towards that tree. It’s as if their ears are telescoped, which lets them hear the lunch bell from wherever it’s ringing. This gives them access to food that would otherwise be inaccessible at the time,” explained Rasmus W. Havmøller, a postdoctoral researcher at the Natural History Museum of Denmark.

The study authors explained that the eavesdropping strategy is not just a convenient way to get a little extra food for themselves – it can play a vital role for animals. There is a season each year when food becomes very scarce in Panama, and many species must depend on almond trees for the majority of their food, including the groups observed for the study. 

“During this season, there is incredibly little to eat in the forest – other than the prodigious quantities of fruit from this one type of tree. However, terrestrial animals can’t access these fruits unless monkeys drop them. For these animals, the eavesdropping method means that they gain access to food in greater quantities and far sooner than the long time it would take if the fruits were left to fall on their own. And during some periods, it is crucial for their food gathering,” said Linnea W. Havmøller.

Ramus W. Havmøller said that in the bigger picture, this means that in areas where monkeys have been removed from the local environment, there can be a negative cascading effect. “Not only will the species of mammals which depend on the fruit being dropped by monkeys suffer – there can be an impact on the entire rainforest ecosystem because terrestrial fruit-eating animals help disperse the seeds that allow the forest to reproduce.”

For the investigation, the researchers collected data using GPS collars, cameras, speakers playing monkey sounds, and traps that collected fallen fruit. The analysis revealed that over 90 percent of the fruit which landed in the traps had bite marks and was half-eaten by monkeys. The fruit that fell outside of the traps was eaten almost immediately.

“I think we’ve underestimated how much mammals interact with each other and how many ways they’re actually connected,” said Rasmus Havmøller. “Eavesdropping between species is a new chapter in the behavioral biology of mammals, which provides us with important knowledge about how much the disappearance of one species can impact an entire ecosystem.”

The study is published in the journal Biotropica.

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By Chrissy Sexton, Earth.com Staff Writer