Humans and wild animals often help each other out, but the relationship is usually accidental. For example, birds of prey sometimes follow farm equipment through fields because the hardware flushes small animals out. Humans don't help the birds intentionally, and we don't gain anything from them. For truly cooperative relationships, you generally have to look to animals we've domesticated.

Generally, but not exclusively. There's an African bird called the honeyguide that helps humans find bees' nests. The humans get the honey, while the birds feast on the wax left behind (the honeyguides were first formally described after they were witnessed eating some candles). Now, new research shows that the birds can specifically respond when a human makes a call that indicates they're interested in finding honey.

Honeyguides inhabit an area of Africa that includes Tanzania and Mozambique. When they're in the mood for beeswax, they approach a human and start making a chattering call. This call is distinct from the call they use to communicate with each other, and it's accompanied by very specific behavior: the bird flits from tree to tree in the general direction of a bee's nest. Once the nest is located and opened, the human comes away with honey and leaves the wax behind for the honeyguide to eat.

It's an extremely effective mutualism. Once the guiding process started, researchers found that three-quarters of the searches ended in the discovery of a bee's nest.

The people who gather honey in the area inhabited by honeyguides have their own call to indicate when they're ready to go on the hunt. Researchers describe it as "a loud trill followed by a grunt: 'brrrr-hm.'" The honey hunters told researchers that they'd learned this call socially—their parents or other family members typically taught it to them. So the researchers decided to test whether it was effective.

To do so, the researchers recorded the call, along with two controls: humans saying the local word for honeyguide and the call of another bird. They played these over speakers and recorded what happened next (which you will probably believe and, if not, there's data). The "let's go find honey" call attracted a honeyguide two-thirds of the time, while the control noises only drew one at about half that frequency.

But even when honeyguides responded to the two control noises, they tended to give up on the search quickly. Only about 15 percent of the searches that started with the control noises resulted in the discovery of bees' nests, while over half of the searches that started with the appropriate call ended in honey.

What's striking about this research is that there's nothing special about the call. In other areas of Africa, completely different noises are used to attract honeyguides. Birds learn a lot of non-instinctual behavior from their parents, but that can't be the case here. Honeyguides are parasites, laying their eggs in the nests of other bird species that then raise their young.

The authors suspect that honeyguides learn to respond to the call by observing the success of their peers. Juvenile honeyguides, which look somewhat different, are mistaken for a different species by the people who gather honey, largely because they don't respond to the humans' requests for help.

While there are anecdotal reports of humans calling wild dolphins for a mutually beneficial search for food, this new research is the first time that this sort of behavior has been described in this sort of detail. And it's happening in a species that doesn't have anything like the mental horsepower of a dolphin.

Science, 2016. DOI: 10.1126/science.aaf4885 (About DOIs).