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VOCAL SIGNALS OF THE VILLAGE WEAVER: A SPECTROGRAPHIC KEY AND THE COMMUNICATION CODE

Abstract Vocal signals of a species are social signals and guides to its social life. Sound spectrograms were made of 21 of the 26 vocal signals in the extensive vocal repertoire of the African Village Weaver (Ploceus cucullatus). A spectrographic key to vocal signals helps make these signals comparable for different investigators. Short-distance contact calls are given in favorable situations and are generally characterized by low amplitude and great brevity of notes. Alarm cries are longer, louder, and often strident calls with much energy at high frequencies, whereas threat notes, also relatively long and harsh, emphasize lower frequencies. Each male displays his newest nest in a colony with an individually distinctive call to unmated females. The most harmonic calls of the species include a loud call by a male when an unmated female first enters his nest, and also very soft, brief notes given by parent birds to attract a fledgling. Males use somewhat different songs to defend territory, for courtship, and for advertisement. Application of Darwin's (1872) principle of antithesis suggests that vocal signals are composed of basic elements that vary in duration, frequency, loudness, and tonality of notes. These variations can be arranged in pairs of opposite extremes serving to reduce ambiguity in signals, in effect a communication code. At the same time, other selection pressures can enter in according to circumstances to modify the expression of this basic code in evolution.