An African bird called the Greater honeyguide is famous for leading people to honey, and a new study shows that the birds listen for certain human calls to figure out who wants to play follow-the-leader.
The finding underscores the unique relationship that exists between humans and this wild bird.
"They're definitely not domesticated, and they're in no way coerced," says Claire Spottiswoode of the University of Cambridge in the United Kingdom. "And they're not taught in any conventional way as well. Humans are not deliberately going out there and training honeyguides."
She first heard of the honeyguide as an 11-year-old child in Cape Town, South Africa, where she went to a meeting of her local bird club and heard a lecture from the pioneer of honeyguide studies, a scientist named H. A. Isack.
In 1989, he published a rigorous analysis in the journal Science showing that the legends about the honeyguide were true: The birds will flutter in front of people, tweet, and fly from tree to tree to guide hunters to bees' nests that are hidden inside the trunks of hollow trees.
"By following honeyguides, human honey hunters can really increase their rate of finding bees nests," says Spottiswoode.
The idea of a wild bird communicating with people in this way seemed almost magical to Spottiswoode. And, she learned, the birds got something, too. After hunters subdued the bees with smoke and hacked open the tree to harvest the honey, the birds ate the discarded beeswax — their favorite food.
Spottiswoode grew up to become a bird researcher, and now she's done her own rigorous study of honeyguides in Mozambique. There, honey hunters who follow these birds rely on a distinctive call.
"It's a rather unlikely noise," says Spottiswoode, who says it sounds rather like a "brr" sound followed by a grunt.
What Spottiswoode wondered is whether that strange call meant anything special to the bird. To find out, she did a study that compared the birds' response to this call with their response to other non-human and human sounds.
What she found is that the random sounds didn't really appeal to the birds. They'd guide people only about a third of the time.
But when the birds heard the special call, they'd guide people two-thirds of the time.
Overall, making the special call more than tripled a hunter's chance of finding honey. The study appears in the latest issue of Science.
But the dry analysis doesn't really capture how Spottiswoode felt as she talked to a little wild bird that listened and led her through the trees.
"I don't think I've ever had as much fun in my life," she laughs. "It was tremendously good fun."
"The new finding shows that honeyguides pay special attention not just to sounds made by humans, but specifically to the sounds that are designed by humans to attract honeyguides," notes Richard Wrangham, a biological anthropologist at Harvard University and one of the few researchers in the world who has given much thought to honeyguides.
"This is really an extraordinary relationship," he tells The Salt. He believes that "the critical feature of the relationship is the fact that humans have fire as well as axes" — the tools that let them harvest honey.
That's why Wrangham thinks this collaboration might go back more than a million years. The birds may have evolved an innate desire to guide people to honey.
Still, they're probably not born knowing what human sounds to listen for. That's because people in different parts of Africa call the birds in different ways.
Brian Wood, of Yale University, has worked with the Hadza foragers of northern Tanzania, who whistle at the birds. He's learned that these people will hide and burn honeycomb to keep the birds hungry, so that they'll be willing to guide again.
"The relationship is likely to be thousands, even millions of years old, but the relationship certainly has changed through space and time — involving different acoustic attractors and different forms of 'repayment' to honeyguides," Wood told NPR in an email. "In some areas birds are actively repaid by human honey hunters and in other places and times, humans actively reduce the bird's 'payoff'. The relationship thus involves elements of both mutualism and manipulation."
He said the new study is important, because it verifies what honey hunters believe about the effect of specialized calls on their work.
"Humans use diverse forms of acoustic signals to attract honeyguides, included spoken words, shouted words, whistles, and other calls (like the Yao brrr-hmm) to attract honeyguides. All these strategies are the product of our species' intelligence and some of them rely upon our capacity for language," he said.
He says he and Spottiswoode are now working together to understand what kind of learning — both within and between species — are involved in these honey-hunting collaborations.
Honeyguides lay their eggs in the nests of other species, so young honeyguides aren't raised by parents that can teach them the ways of humans, notes Wrangham.
"I hope they will test the idea that the way that young birds learn to pay attention to the call is by observing adults," he says.
He also wonders what happens to these birds in parts of Africa where people stop hunting for honey because it's easier to just go to a store. "Do their numbers fall? Do they lose the guiding habit? Should managers arrange for honey collection in national parks in order to promote honeyguide conservation?" asks Wrangham. "These would be important questions to investigate."