George Sutherland of Maori Hill, asks :-

How come when I put out sugar and water in my bird feeder, within minutes a tui, bellbird, or waxeye, appears, followed by lots of its mates. Can they communicate?

Doug Armstrong, a wildlife ecologist at Massey University, responded.

I am not aware of any deliberate communication in these species, but I would not be surprised if such communication exists in waxeyes given that they seem to constantly give soft contact calls to one another.

Such communication clearly exists in sparrows, i.e., if you throw pieces of bread on the lawn, you will hear the first sparrow "chirp" to let the other sparrows know there is food there. The amount of chirping is related to predation risk, so it seems that the first sparrow wants to attract others to make it safer from cats etc.

With tui and bellbirds, I think that they watch each other closely, so if one bird discovers a food source, the others are quickly onto it. In my experience, feeders put out for honeyeaters (the family that tui and bellbirds below to) can go undiscovered for days, but then everybody quickly knows about it once the first bird discovers that it is a food source. Funnily enough, I never had any success getting the tui on my property to use feeders I put out for them.