Directional Differences in the Sound Intensity of Ruffed Grouse Drumming

STUDENTS have long been intrigued by the drumming of the Ruffed Grouse (Bonasa umbellus). Physically, drumming is a wingbeating display performed from a stationary position, usually upon an elevated object known as a "drumming log." The drumming performance has been described in detail by Bump eta]. (1947: 274-276) and Hjorth (1970: 220-225). Functionally, drumming is believed to correspond fully to song, which is lacking in the species (Hjorth 1970: 497), to facilitate spacing of males (Alien 1934, Fow]e 1953: 91), stimulate female sexual development (Hjorth 1970: 497), and to attract females (Alien 1934, Brander 1967). Numerous ideas have been advanced about how the noise is produced (cf. Bump eta]. 1947: 276-278). Recent]y, Hjorth (1970: 225-233) has suggested new explanations of the related questions of how the sound is generated and how the grouse is able to maintain its balance during the drumming performance. The number of wingbeats in and the duration of a drum are variable both within and among individuals (Aubin 1972). The drumming sound is audible to the human ear up to distances of % to • mile (Sumanik 1966: 38) or more. Although grouse have been reported to turn their heads in reaction to neighbors' drums (Hjorth 1970: 489), no reports of how far a grouse can perceive drumming are available in the literature. Use of the radiote]emetric method has enabled the remote determination