Eavesdropping is typically seen as a vice. But in the animal kingdom, sometimes it’s a very useful strategy: Animals have been observed eavesdropping on other animals to do useful things such as detecting predators or finding a good site for a nest. It got a team of scientists wondering whether terrestrial mammals such as coatis and agoutis eavesdropped on eating monkeys to find food.
To find out, they conducted a series of experiments in the Panamanian rainforest. They put GPS collars on capuchin and spider monkeys, who eat fruit loudly and messily up in the trees, as well as on coatis, raccoon-like animals which live on the ground and have been seen eating fruit dropped by the monkeys. They also set up cameras to record the animals’ eating habits, and set up fruit traps to examine the kind of fruit that fell to the ground. Separately, they played recordings of monkey sounds to see whether the terrestrial animals such as coatis and agoutis—larger cousins of the guinea pig—would come when they heard them.
The fruit traps showed that a vast majority of the fruit on the ground was dropped by monkeys, emphasizing their importance to the terrestrial animals. The GPS collars and cameras showed that agoutis came to trees more quickly, and coatis spent longer periods of time at the trees, when the monkeys were there. The experiments playing monkey sounds didn’t provide conclusive evidence that the terrestrial mammals came to the trees because they heard the monkeys, but it didn’t rule it out. Scientists will have to do more spying and eavesdropping themselves to find out for sure.