WASHINGTON — In Mozambique’s woodlands, the sound of sweet evolution is at work.
Over the centuries, through genetic and cultural adaptation, humans and a wild bird species have learned to work together with a simple sound: “Brrr-hm.” When human honey-hunters make that call, the bird called the honeyguide does its namesake job with incredible accuracy, leading people to hidden bees’ nests.
Scientists put this ancient practice to the test and it passed with high flying colors. When biologists compared the “brrr-hm” sound to other sounds, the traditional sound sent the honeyguides to hidden bees nest three times more often than the control sounds, according to a study in the journal Science Thursday. When you make the right noise, you end up with honey 54 percent of the time, compared to 16 percent of the time with the wrong noise.
“It’s an exchange of information for skills,” said study lead author Claire Spottiswoode, an evolutionary biologist at the University of Cambridge. It happened to her personally. She failed to find bees nests until her companion made the right noise and was rewarded with a honey that’s “very rich, very flavorful. It catches at the back of the throat.”
The honeyguide has a unique ability to find bees’ nests. Scientists aren’t quite sure how it works, but it likely has to do with an advanced sense of smell, Spottiswoode said. Still, there’s a problem: These nests are stuck in trees that are difficult for the birds to reach. Even worse, the bees sting the birds, sometime to death.
The people of the region, who make a living on the honey, have axes and other tools that can get at those nests and they use smoke to chase the bees away, reducing the stinging problem. But the people, called the Yao, can’t easily find the hidden bees.
But over the centuries the honeyguide and the Yao people have developed the call. When honeyguides hear the call they also make a noisy response and then fly from tree to tree, leading the honey hunters to the bees. The humans open up the tree, smoke out the bees and take the honey. The birds eat the wax, Spottiswoode said.
While humans train dogs and other animals to hunt, this is different because those animals are domesticated and these are wild birds, not trained specifically by humans, Spottiswoode and other scientists said.
Richard Wrangham, a Harvard University evolutionary biologist who wasn’t part of the study, said this is the most advanced bird-mammal relationship in the world.
It’s clear that the birds have adapted in an evolutionarily way through natural selection, but for people the arrangement is probably more cultural, Spottiswoode said.
In Tanzania, humans use a different sound successfully with honeyguides, said Spottiswoode and Yale’s Brian Wood.
Despite their sweet name and helpfulness to humans, the honeyguides aren’t so benevolent. The honeyguides are ruthless parasites, depositing their eggs in other species’ nests and then, when the baby honeyguide hatches, it kills its foster siblings with a beak that has a hook at the end.