The Master of Game 1406-13 Mostly based on Livre de Chasse, by Gaston Phoebus, 1387-88, but with five additional chapters and some omissions of content not relevant to English hunting.
The Art of Hunting. Original Anglo-Norman text c1325, translated into English c1425.
The number of collective nouns is small compared to the erudite profusion invented in the mid and late 15th century. Of beasts that are hunted, The Art of Hunting mentions only herds of harts, hinds, bucks and does, sounders of wild boar and bevies of roe deer. The Master of Game also lists routes of wolves and seven different terms for droppings, depending on the beast responsible.
Other pre-15th century sources refer to a covey of partridges, a bevy of herons, and a sounder of starlings in English and of jays and finches in French.
Incidentally, William Twiti, author of the Art of Hunting, had a cameo role in The Once and Future King.