Humans and wild birds communicate with each other so that they can seek out honey. The unique relationship between people and the honeyguide bird across much of sub-Saharan Africa was thought to be more of a one-way conversation, but now it seems that both species are listening out for each other.

Flitting from tree to tree, the greater honeyguide (Indicator indicator) leads the humans in the direction of nearby beehives. This is obviously beneficial to the humans as they are shown a delicious house of bees, but also to the bird as it hangs around and waits for them to subdue the bees using smoke, and then break into the hive to get at the sweet honey within. When done, the person will then provide the bird with the wax, in addition to the tasty larvae hidden within. In this relationship both partners benefit, but until now it was only thought that it was the birds that got the humans attention by calling to them.

It has now been found that this the communication between the two species that form this unique relationship is, in fact, two-way: the birds not only recruit the humans, but the humans will recruit the birds. To test this, the researchers recorded a specific call that the hunter-gatherers make to talk with the passerines – a "brrr-hm" noise (which you can hear below) that is learned by children from their fathers – while walking through the bush in Mozambique where the birds live, and compared it with other random noises such as talking.

They found that the playing of the traditional "brrr-hm" call increased the chance that they would recruit a honeyguide from around 33 percent to 66 percent, and that the overall probability that the human would be shown a beehive more than trebled from 16 percent to 54 percent, when compared with the control noises. This shows how the two engage in two-way conservations. But even more, depending on where in Africa you look, the humans who recruit the birds make differing noises.

“Intriguingly, people in other parts of Africa use very different sounds for the same purpose. For example, our colleague Brian Wood's work has shown that Hadza honey-hunters in Tanzania make a melodious whistling sound to recruit honeyguides,” explains Claire Spottiswoode, who led the research published in Science. “We'd love to know whether honeyguides have learned this language-like variation in human signals across Africa, allowing them to recognize good collaborators among the local people living alongside them.”

Humans have been using animals to help them get food in a number of different ways, from cormorants catching fish to the classic dogs assisting in hunting. But in most cases, these relationships rely on the humans domesticating the animals and training them to do the specific task. Examples of such relationships existing between humans and wild-living animals is much rarer, making the one that has sprung up between the honeyguides and people even more interesting.

“What's remarkable about the honeyguide-human relationship is that it involves free-living wild animals whose interactions with humans have probably evolved through natural selection,” says Spottiswoode, “probably over the course of hundreds of thousands of years.”

^{The remains of a traditional honey harvest in Mozambique. Claire Spottiswoode}