it would actually be interesting to see how many zoo signs have "blue-eared", "white-eared" and "brown-eared" for their eared pheasants. I bet there are a lot!
a lot of people do, same as for crowned-crane and similar names. I just think it looks ugly. The modern fad for shoe-horning of hyphenisation into established non-hyphened bird names is a very contentious issue amongst birders.
I tend to be in favour when it's to avoid misunderstanding - as with eared-pheasant or crowned-crane, but I'm less sure about it in cases like green-pigeon where it seems to be done to give a more differentiated common name when the existing one is fine.