When honey-hunters in Mozambique call out to birds in the hopes that their feathered companions will lead them to honey, the birds, in fact, recognize and respond to these specialized calls, a new study confirms. The results reveal how birds are able to attach a specific meaning to the human's call for cooperation, representing a rare case of mutualism between humans and a wild animal. Indicator indicator is a species of bird that's known to act as a honeyguide for humans, flitting from tree to tree to indicate where beehives are hidden above. Alone, the bird is unable to crack open a beehive to enjoy the beeswax within, but when humans harvest a hive for honey, they leave the wax behind - a delicious treat for I. indicator. In Mozambique, the Yao tribe uses a distinct call to attract I. indicator as a honeyguide, producing a loud trill followed by a grunt (see audio). Claire Spottiswoode and colleagues interviewed 20 Yao men who use the 'brrr-hm' call, all of whom say they learned it from their fathers and that it's the best way of attracting a honeyguide. To confirm the efficacy of this mutualistic relationship, as well as the call itself, the researchers trailed honey-hunters. They found that 75% of guiding events led to the successful discovery by humans of at least one bees' nest. Next, to test whether honeyguides associate 'brrr-hm' with a specific meaning (a higher payoff from cooperation), they made recordings of this call and two kinds of 'control' sounds. Then, an author and two local honey-hunters walked while playing back one of the three acoustic cues every 7 seconds over 15 minute intervals. Birds were much more likely respond to the 'brrr-hm' call made to attract them than they were to the other sounds, the researchers found. The traditional 'brrr-hm' sound increased the probability of being guided by a honeyguide from 33% to 66%, and the overall probability of being shown a bees' nest from 16% to 54% compared to the control sounds.
Yao honey-hunter Orlando Yassene holds a wild greater honeyguide female (temporarily captured for research) in the Niassa National Reserve, Mozambique. This material relates to a paper that appeared in the July 22, 2016, issue of Science, published by AAAS. The paper, by C.N. Spottiswoode at University of Cambridge in Cambridge, UK, and colleagues was titled, "Reciprocal signaling in honeyguide-human mutualism." Credit: Claire N. Spottiswoode
source: American Association for the Advancement of Science