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A comparison of the origin and temporal arrangement of pulsed sounds in the songs of the Grasshopper and Sedge warblers, Locustella naevia and Acrocephalus schoenobaenus
Author(s) -
Brackenbury JohnH.
Publication year - 1978
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/j.1469-7998.1978.tb03275.x
Subject(s) - repetition (rhetorical device) , biology , acrocephalus , rhythm , pulse (music) , acoustics , communication , interference (communication) , physics , computer science , linguistics , channel (broadcasting) , optics , population , telecommunications , psychology , philosophy , demography , sociology , detector
The songs of the two British warblers Locustella naevia and Acrocephalus schoenobaenus were examined by means of oscillographic recordings. Both songs are composed of pulsed elements arranged in rhythmical successions. The song of L. naevia is simple and stereotyped consisting of a succession of paired pulses with a repetition frequency of 26 Hz. The song of A. schoenobaenus contains many different phrases each consisting of a succession of identical chirps. Chirps consist of successions of pulses, the number and repetition rate of which vary from phrase to phrase. The songs are discussed in relation to the physiology of sound production and to the way in which information is encoded into sound signals. It is proposed that pulses are produced by the syringeal muscles, whilst the rhythm, tempo and duration of chirps and phrases are controlled by the respiratory muscles. A distinction is drawn between the action of the extrinsic syringeal muscles, which may produce low frequency pulses, and the intrinsic syringeal muscles, which may produce high frequency pulses. The codal format in both songs is shown to be highly redundant, being based on the repetition of identical units of information. This device reduces the possibility of distortion of meaning by interference from environmental noise but limits the information carrying capacity of the code. The method of pulse coding is shown to be particularly well suited to the avian auditory system which is adapted to receiving and processing rapid transient signals. This ability is in part attributable to the fine discrimination of time and amplitude changes in the cochlea.