Broadcast Distance of the Mutual Display Call in the Emperor Penguin

AbstractIn the colonial emperor penguin Aptenodytes forsteri, the broadcast distance of the mutual display call (the distance over which the individual information conveyed by the call is transmitted) was determined. The variables measured were (1) the sound amplitude that averaged 94.8 dB SPL for birds facing toward the microphone and 85.7 dB SPL for birds facing away, (2) the sound attenuation that decreased with about 6 dB per doubling distance, (3) the ratio of the signal to the background noise of the colony which was 20-25 dB during the rearing period of chicks, and (4) the degradation of the signal structure by the scattering medium (penguin bodies) and distance, which affected the timbre, but not the two fundamental frequencies of the call that produced a beat phenomenon. This distance, 4-7 m indicates that the call is transmitted at short- or medium-range, and corresponds closely to the distance covered between two stops where a parent in search for its chick calls. The beat phenomenon undegraded by the scattering medium and distance is likely to serve individual recognition, assuming there is a relationship between the broadcast distance and the functional structure of emperor penguin call.