They learn from videos!

[Pajarita]

A study done with blue tits showed that they learned to avoid bad-tasting food from watching other tits eat it and react with disgust in video - conversely, one could say that seeing another bird eating a certain type of food with relish would 'inspire' them to try it, something that we, old timers of multiple parrot keeping, have been saying for a long time but which was impossible to try with single birds. Only now we know that we can use videos of other parrots eating to teach them!

https://www.newscientist.com/article/22 ... her-birds/