Nice article, thanks! I was glad to read that they mentioned that chickens have a good two dozen distinct vocalizations. I remember reading that in one of my old banty books and the thought then was that the extensive vocabularies of chickens was due to how their ancestors live, in the sometimes dense edge vegetation of jungles, where visibility was sometimes compromised, but they could always talk to one another, even when a distance apart.
Another thing I like about chickens (although they do need access to the outdoors for this) is that they can also learn the languages of other bird species, most particularly alarm calls, which I believe are thought to be somewhat universal as bird-speak goes. I noted this just a couple of days ago when there was another small-bird hawk swoop over my neighbour's feeders. A blue jay there sounded the aerial predator alarm and a couple of my brown-egg layer hens, who were out in the open by themselves, instantly sprinted for cover--man! did they move! All the older chickens also go alert when they hear nearby robins and sparrows tut-tut-tutting. They've learned that such calls mean a ground predator, maybe just the neighbour's cat, but it COULD also be the neighbourhood fox...