The Importance of Directional Sound Radiation in Avian Vocalization

Many studies show the importance of frequency structure and timing characteristics for acoustical signals (e.g., Thorpe 1961, Hinde 1969), but we know little about the sound pressure levels and spatial radiation patterns of such signals. Here I offer evidence for directional radiation of certain calls of the Black-capped Chickadee (Parus atricapillus) and discuss ways in which selection may favor directional beaming. Most of the scant literature on radiation