Proposal for a new term ‘echeme’ to replace ‘chirp’ in animal acoustics

The term ‘chirp’ as defined by Broughton (1952) and varied by him (1963a, b) is shown to be both inadequate and potentially misleading, particularly in the light of the principles of measurement of the time-parameters of insect song, which are reviewed. It is important to include, in the measured duration of a given element, not only the durations of its constituent sub-elements plus the intervals between them, but also an estimate of the interval that would have followed the last sub-element, had the emission been prolonged further.

‘Chirp’ should be totally restricted to initial, empirical descriptions of sounds that appear undivided to the human ear (or ultrasonics of corresponding length). For a first-order assemblage of syllables, the term ‘echeme’ with a highly relevant etymology, is proposed.

In early insect-acoustics studies, Broughton (e.g. 1963a), seeking mainly to follow the admirable German terminology of Faber (e.g. 1953) and Jacobs (e.g. 1953), and to combine it with accepted physical terms, proposed certain English equivalents, many of which (such as ‘pulse’, ‘syllable’, ‘sequence’) have proved adequate in the years since then.

The term ‘chirp’, however, had been rather loosely and inappropriately used in still earlier studies (Broughton, 1952, 1953; Chavasse et al., 1954) as the equivalent of Jacobs' Silbe (syllable = sound or ultrasound corresponding to one stroke of the singing apparatus). This was in direct conflict with the dictionary usage of ‘chirp’ as a sound that appears unitary and undivided to the unaided human ear (M. Duijm, personal communication in 1962).

This is why, in the 1963 revision, Broughton abandoned the use of chirp as equivalent of Silbe, in favour of the direct translation, syllable; and proposed restricting ‘chirp’ to usage as a term for the first-stage description of a unitary-sounding element of an animal emission, regardless of its composition in terms of physical units (pulses) or physiological units (syllables). Thus, the song of Chorthippus brunneus (Thunberg)(Orth., Acrididae) sounds unitary to the human ear, but consists of a rapid series of sounds each corresponding to one stroke of the apparatus: it is therefore, according to the 1963 system, a ‘polysyllabic chirp’ (Fig. 1)-a chirp that happens to be a first-order assemblage of syllables. By contrast, the song of Chorthippus parallelus (Zetterstedt) is a clear series of unitary sounds each visibly produced by one movement, and is therefore a ‘sequence’ of ‘monosyllabic chirps’ (Fig. 2).