Blackcock
2 of the 7 encyclopedias on this shelf carry an entry for Blackcock. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a northern grouse of the Old World. It is closely allied to our partridge and prairie hen . It lives on leaves, buds, and berries in the mosses of northern Britain, Scandinavia, Russia, and Siberia. The male weighs about four pounds and is of a bluish-black color. The female is gray and weighs half as much. Large numbers of the males are brought to the London market, the female being left by common consent to breed unmolested. The handsome male, with a scarlet patch over his eye, and a call likened to the whetting of a scythe, is the bird of which Scott, with Ellen's Isle in mind, says, "At noon the blackcock trims his jetty wing." See Grouse 2026 Editor's Note: This bird gave biology a word: the communal display ground where the males strut and spar for watching females is a "lek," and lek mating is now a standard concept used for everything from grouse to fish to fruit flies. The black grouse itself has declined steeply in Britain, its moorland habitat shrinking. (Ed: BR 2026-06-21)
Collier's New Encyclopedia (1921)
a name for the male of the black grouse or black game, called also the heathcock (tetrao tetrix). The female is called the gray hen, and the young are poults. The blackcock, as its name imports, is black, having, however, white on the wing covets and under the tail, the two forks of which are directed outward. It is about as large as a domestic fowl. It is found in some abundance in Scotland and less plentifully in England. The eggs are from 6 to 10 in yellowish gray color, number, of a blotched with reddish brown.