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Dietmar Todt and Anne Fiebelkorn

Abstract

I. The antiphonal duets of Cichladusa guttata (Turdidae, Aves) are often accompanied by spectacular wing movements. We have analysed the display, timing, coordination and function of this behaviour using sound films, audio and video recordings of free living and captured birds (Figs 1, 2). 2. The vocal duet contribution of the members of a pair appear well coordinated in timing, normally with no overlap of notes. Specific types of duet notes of the male or the female can release wing beats in the male (response time: 380 ± 80 msec.), but not vice versa. Additionally, note utterance can trigger the wing beat start (reaction time 30 ± 15 msec.) in the same bird, which is normally the male (Figs 4, 5, 6, 7, 8). 3. Wing beat performance is also affected by two further variables: "duet activity" and "wing beat periodicity". The duet activity which changes relatively slowly can be estimated from parameters of the behaviour (vocal density, vocal power, etc.). Auditory stimulation with conspecifics songs raises duet activity and thereby facilitates wing movements. This does not affect the "component of wing beat periodicity", which has a cycle length of 540 msec. (Fig. 3; Tab. i). 4. Normally, both wings are moved synchroneously. Experiments with restricted space on one side of a songster showed that wing beats can be blocked unilaterally. While a space restricted wing remained unmoved the other wing operated in full coordination to the duet program. 5. Due to the different affectations wing "escort" is optional. It occurs regularly, but, with high flexibility. When the variables promoting wing beats result in high values, high wing beats occur, when the values are low, low or no wing beats are observed (Fig. 9). 6. (Wing beats are supposed to support the general function described for the vocal duet contributions.) Specific functions discussed for the non-vocal contributions are: focussing and directing of attention (spectacular display via an additional signal channel; avoidance of habituation (optional and flexible occurrence) ; preventing distance signalling from disturbances in the acoustic channel (noise produced by birds singing simultaneously) ; distance measurement by identification of phase shifting between vocal and non-vocal behavioural rhythms.