Japanese deer 'eavesdrop' on monkeys for food

Sika deer "eavesdrop" on monkey chatter in order to find food, say scientists. A team from Kyoto University, Japan, tested how macaque monkey calls affected the feeding behaviour of the deer that live on Yakushima Island. Previous research has focussed on species "listening to" one another to avoid danger. But when scientists played macaque calls from hidden speakers, the deer gathered nearby, indicating that they associate the sounds with benefits. The results were published in the journal Behavioural Processes. Dr Hiroki Koda who led the study said it was a good example of "possible interspecies communication" and that the deer seemed to be eavesdropping as a "foraging strategy". Yakushima Island lies to the south of Kyushu, Japan, and is protected by its Unesco world heritage status. The island, which includes the ancient and famous Yakusugi Forest, is home to 1,900 species and subspecies of fauna. The deer and macaques that live there feed on the fruit of camphor trees. Researchers first reported the deer "gleaning" fruit from beneath trees where monkeys were feeding in 2004. Dr Koda from the Primate Research Institute at Kyoto University wanted to investigate how the deer were able to follow the monkeys to foraging sites. After hiding speakers in the forest he played recordings of calls commonly made between the monkeys during feeding sessions. 

In his experiments, Dr Koda found that groups of deer often gathered near speakers during the playbacks, but they rarely gathered during "silent" periods when no calls were played. Dr Koda now aims to investigate whether the deer can differentiate between the various food calls made by the monkeys. He explained that there were "many common food items" that both deer and macaques ate. "But of course," he said, "some food items are used only by macaques, or only by sika deer. "When macaques make food-associated calls [for] "macaque fruits", sika deer might not [respond]."