The article is pretty good taking into consideration that they are talking about all parrots... I personally prefer it when they talk about a species in particular or a very similar group of species -like pyrrhuras or amazons, for example. The reason is that, sometimes, what means one thing for one species, means the opposite for another. For example, it says here that clicking means the parrot is interested in something but, for a YNA, it means that is in high alert and ready for aggression.
https://www.pets4homes.co.uk/pet-advice ... happy.html