The ruffed grouse (Bonasa umbellus) is a medium-sized grouse occurring in forests from the Appalachian Mountains across Canada to Alaska. It is non-migratory.

The ruffed grouse is sometimes incorrectly referred to as a "partridge", an unrelated phasianid, and occasionally confused with the grey partridge, a bird of open areas rather than woodlands.

The ruffed grouse is the state bird of Pennsylvania, USA.

Taxonomy

Bonasa umbellus was first described by Linnaeus who classified it as Tetrao umbellus, placing it in a subfamily with Eurasian grouse. The subfamily Bonasa was applied by British naturalist John Francis Stephens in 1819. Ruffed grouse is the preferred common name because it applies only to this species. Misleading vernacular names abound, however, and it is often called partridge (sometimes rendered pa'tridge, or shortened to pat), pheasant, or prairie chicken, all of which are properly applied to other birds. Other nicknames for ruffed grouse include drummer or thunder-chicken.