Hunter calls. Bird responds. And together they find honey.

The honey-hunter lets out a long trill, followed by a sharp grunt.

Brrr-hm!

On cue, a small bird flies to the hunter and responds with its own chattering noise. The greater honeyguide flits from tree to tree, searching for a beehive.

Over thousands of years, honeyguides, named for their unusual relationship with people, have gained the ability to recognize and respond to specific calls made by the honey-hunters of Mozambique and Tanzania, according to a study published Thursday in Science.

The relationship represents a rare example of cooperation between humans and wild animals. Humans have the tools to avoid angry bees and break open the nest; the birds have the nose to find them.

The hunter, seeking an important source of food, smokes out the bees, chops the tree down and extricates the hive and precious honey hidden within. Meanwhile, the bird waits nearby to claim its finders fee: the leftover wax which it happily devours.

As far back as 1588, outsiders have observed the dynamics between honey-hunter and honeyguide. More than 400 years ago in modern-day Mozambique, Portuguese missionary Joao dos Santos often noticed a small bird flying into his church to nibble on the wax candles. He also observed the little bird leading men to beehives by calling to them and flying from tree to tree.

But how do we know if this human-bird relationship is built on communication instead of coincidence or a myth? To find out if the honeyguides actually help the hunters locate bees’ nests, the authors of the new study designed a series of experiments.

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Claire Spottiswoode, an evolutionary biologist at the University of Cambridge and University of Cape Town, and colleagues started by interviewing 20 Yao men living in Niassa National Reserve in Mozambique about the origins of the brrr-hm signal, and all had the same answer.

“When asked why, [the honey-hunters] reported that they learned [the call] from their fathers and that it is the best way of attracting a honeyguide and maintaining its attention,” Spottiswoode wrote with Keith and Colleen Begg.

Next, they followed the honey-hunters following the honeyguides. By trailing the birds, the hunters found beehives 75% of the time, the study found.

The researchers also wanted to know if the birds associate the Yao hunters’ brrr-hm signal with a specific meaning, in this case a reward for working with the humans. If so, the study’s authors reasoned, the honey-hunting sound should be more likely to attract a honeyguide than other sounds.

Again, the scientists followed the honey-hunters. This time, however, the researchers played recordings of the signal, a human voice or sounds from a ring-necked dove.

Across 72 attempts, the specialized honey-hunting call had a 66% chance of attracting a guide; the other sounds had a 33% chance. The honey-hunting signal also increased the chance of a bird leading the humans to a beehive from 16% to 54%.

“Production of the honey-hunting sound more than tripled the probability of finding a bees’ nest,” the authors wrote. “This finding experimentally validates the honey-hunters’ claims that the honey-hunting sound improves their foraging success.”

Throughout history, humans have trained and domesticated animals, including dogs, falcons and cormorants, to help search for food. The African hunters’ relationship with honeyguides is unusual because the birds remain wild.

People don’t train the birds, and it’s unlikely they’re trained to respond to humans’ calls by their parents, either. Adult honeyguides lay eggs in the nests of other bird species. When they’re just days old, the babies use their sharp hooked beaks to kill the host’s hatchlings as they emerge from their eggs.

So how do young honeyguides learn how to recognize hunters’ calls?

One hint lies about 600 miles away from the Yao people. Another group, the Hadza of Tanzania, use a melodious whistle to attract honeyguides. It’s possible young honeyguides, like their human partners, learn the local honey-hunting calls by observing other birds near beehives. The result: “a local cultural tradition among honeyguides that reflects the customs of their human collaborators,” the authors suggest.

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