So, at work today, Ed asked me if young grouse were really called 'poults' or if that was just baby pheasants and turkeys? Good question.
I think the short answer is that it's not technically, ie. lexicologically, wrong to call them poults, but recent convention has been to call young grouse chicks instead.
For example, the Oxford English Dictionary defines poults as: "The young of the domestic fowl, a chicken; also of the turkey, pheasant, guinea-fowl, and various game birds." The second cited usage of poult from c.1440 is given as: "Pulte, yonge hen, gallinella"; the 1863 citation specifically mentions "Ptarmigan poults, hardly fledged." Ptarmigan, like grouse, belong to the order Galliformes. It could be assumed, therefore, that calling young grouse 'poults' is not out of spirit with the early use of the word.
However, few of the relatively modern sporting writers use anything other than 'chicks' to describe young grouse. I just looked in my books by Norris, Knight, Woolner, and Furtman... none of them use poult. I don't have time to scan all my George Bird Evans books and don't (yet) have a copy of Gardiner Bump's magnum opus on the life-cycle of grouse. But I'm feeling pretty good about correcting myself.
I'm posting the bibliography here because half of the books haven't been reprinted:
a) Charles Norris, Eastern Upland Shooting, with Special Reference to Bird Dogs and their Handling, Philadelphia: J.B. Lippincott Company, 1946;
b) John Alden Knight, Ruffed Grouse, New York: Alfred A. Knopf, 1947;
c) Frank Woolner, Grouse and Grouse Hunting, New York: Crown, 1970;
d) Michael Furtman, Ruffed Grouse: Woodland Drummer, Mechanicsburg, PA: Stackpole, 1999.