Tribesmen and honeyguides share an ancient pact and communicate in trills and grunts, scientists report. The shared goal: beehives full of honey and wax.

Their word is their bond, and they do what they say — even if the “word” on one side is a loud trill and grunt, and, on the other, the excited twitterings of a bird.

In return for revealing the location of natural honey pots, the birds are rewarded with the leftover beeswax, which they eagerly devour.

Now scientists have determined that humans and their honeyguides communicate with each other through an extraordinary exchange of sounds and gestures…

The findings cast fresh light on one of only a few known examples of cooperation between humans and free-living wild animals…

…other examples of human-wild animal cooperation: fishermen in Brazil who work with bottlenose dolphins to maximize the number of mullets swept into nets or snatched up by dolphin mouths, and orcas that helped whalers finish off harpooned baleen giants by pulling down the cables and drowning the whales…

 But for the clarity of reciprocity, nothing can match the relationship between honeyguide and honey hunter…

How the alliance began remains mysterious, but it is thought to be quite ancient.

…“so the relationship could be more than a million years old.”

The bird might even have played a role in the emergence of fully modern humans and their energetically demanding brains…