Diana monkeys and hornbills share a predator, the crowned eagle. Researchers found that hornbills respond to monkey warning calls for crowned eagles and ignore monkey calls that warn of leopards. This demonstrates the hornbill's ability to interpret the monkeys' various calls. The birds only respond to the call that warns of a predator that poses them direct threat (in this case, the crowned eagle). As a ground-dwelling predator, the leopard poses little threat to the hornbills, and consequently the hornbill need not respond to the monkey calls that warn of leopards.
The team, which consisted of biologists Professor Peter Slater and Hugo Rainey as well as primatologist Dr Klaus Zuberbuhler, noted the hornbills' ability to differentiate between and single-out relevant monkey warning calls (for example, warnings pertaining to crowned eagles). The researchers concluded the birds actively interpret the monkey communications.
Previous studies have revealed that monkeys, lemurs, and other mammals listen to each other's warnings. But never before has a study demonstrated communication exchanges between birds and mammals. This study represents the first investigation of its kind and brings to light interesting information about the advanced degree of animal communication.
