They would be whistle sounds, more bird calls than any sort of human speech. The interesting thing about this that they've discovered is that it's only used between humans and birds. Birds don't use it with each other. It has a grammar, so to speak, a directional component. The honey exists in a certain place, so they alert the human. The human follows. They find the honey. The bird needs the human to get the honey out of the tree, to break the tree open, and then the bird actually eats the honeycomb. There are a lot of documentaries on this. Over the years, as we've gotten more sophisticated in recording and then breaking down the recordings and analyzing them, we're able to understand.
Another example would be chickadees, very common birds, and tufted titmice. They have these much more advanced systems of communication, and they go across species as well.
We're hearing that in Australia birds will communicate certain things. I always go back to the example of pets. In pet bird studies on parrots or studies on birds in captivity like crows, we're able to see advanced communication systems. This is something that would definitely be taking place.