Honeyguides respond to particular human signals

“[The call] reliably tells [the bird] that this just isn’t any human, this is a human who wants to cooperate,”

see www.theguardian.com/science/2016/jul/21/sweet-talk-wild-birds-and-human-honey-hunters-converse-study-shows

There is a full write-up on the human-bird mutualism at science.sciencemag.org/content/353/6297/387