The greater honeyguide, Latin name Indicator indicator, is known for guiding people to beehives in the African bush in the hope that the human honey-hunters will leave beeswax behind for the birds to snack on. But if someone wants to be led to the buzzing hive dripping with golden, sticky honey, they might need to know a special password, according to a study lead author Claire Spottiswoode, an evolutionary biologist at the University of Cambridge and the University of Cape Town.
“They told us that the reason they make this ‘brrrr-hm’ sound, when they’re walking through the bush looking for bees’ nests, is that it’s the best way of attracting a honeyguide – and of maintaining a honeyguide’s attention once it starts guiding you,” said Dr Claire Spottiswoode.
This reciprocal communication is unique to the honeyguide-human cooperation. Spottiswoode knows of no other wild animal that both uses and understands cross-species vocal signaling like this to facilitate mutualistic foraging with humans.
The wild partnership can stretch as much as half a mile before the bird arrives at its buzzing destination. When it does, the bird quiets down and settles on a tree. Sometimes that tree contains a beehive and other times it sits nearby its target, waiting for its human partners to spot the hive.
Once the humans find the hive, they get to work. They expertly smoke out the bees before reaching into retrieve their sticky gold or felling the tree for easier access. Meanwhile, the honeyguides wait, in the hopes that the humans will leave behind some beeswax for them.
But, what contribution this sound actually made?
“In particular, we wanted to distinguish whether honeyguides responded to the specific information content of the ‘brrr-hm’ call – which, from a honeyguide’s point of view, effectively signals ‘I’m looking for bees’ nests’ – or whether the call simply alerts honeyguides to the presence of humans in the environment,” said Dr Claire Spottiswoode.
To make that distinction, the team made recordings of the “brrrr-hm” call, as well as of general human vocal sounds such as the hunters shouting their own names, or the Yao word for “honey”. Then, Dr Spottiswoode accompanied two Yao honey hunters on 72 separate 15-minute walks through the Niassa National Reserve.
Sure enough, walks accompanied by the “brrrr-hm” recordings were much more likely to recruit a honeyguide (66% of the time, compared to 25% for the other vocal sounds).
The special call also trebled the overall chance of finding a beehive (a 54% success rate, up from 17% for the other sounds).
“What this suggests is that honeyguides are attaching meaning, and responding appropriately, to the signal that advertises people’s willingness to cooperate. It seems to be a two-way conversation between our own species and a wild animal, from which both partners benefit.“
What do you think about this an evolved, co-evolutionary relationship? J