. Bulletin of the British Ornithologists' Club. 25 [Bull. i977: 97(1)] All bouts of displays that were seen appeared to begin spontaneously, without the presence of a female; but, as already mentioned, display by one male tended to stimulate the other to display. Bouts of display usually lasted for 1-5 minutes. It seemed probable that during the period of observations (7-16 Apr) the local females were not visiting the display grounds, at least during the middle of the day, though the breeding season should have begun. Vocal and mechanical sounds. As mentioned, males call intermitte
. Bulletin of the British Ornithologists' Club. 25 [Bull. i977: 97(1)] All bouts of displays that were seen appeared to begin spontaneously, without the presence of a female; but, as already mentioned, display by one male tended to stimulate the other to display. Bouts of display usually lasted for 1-5 minutes. It seemed probable that during the period of observations (7-16 Apr) the local females were not visiting the display grounds, at least during the middle of the day, though the breeding season should have begun. Vocal and mechanical sounds. As mentioned, males call intermittently when they are present in their display areas. Calls are one- to four-syllabled, abrupt, and either high-pitched or of a nasal quality, or a combination of both. The commonest is a trisyllabic wrrt-pit-arrk (Fig. 1, B), sometimes preceded by a pit to produce a fourth syllable. Less frequently given is a sharp disyllabic ker-^eek, and a monosyllabic %eek similar to, but less loud than, the second syllable of the ker-^eek. Two sounds are associated with the kHz 8 2-. A ~2~ SEC Figure 1. Sonagrams of (A) the mechanical wing-noise {prrt) made during display, and (B) the trisyllabic wrrt-pit-arrk. The mechanical wing-noise consists of two very brief sounds, with energy evenly distributed over a wide frequency range, separated by an interval of about 0-015 sec (4 measured). displays and are described in context below: an explosive, mechanical wing- noise, and a sharp bu2zing call. Backward slide. With its body orientated along or nearly along the perch, head held low, wings raised a little, tail slightly depressed, and legs stretched so that the red thigh feathers show, the bird takes rapid and very short steps backwards for about 15 cm along the perch, so that it seems to slide. At the end of the slide, two things may happen: (1) most often, the wings are sud- denly vibrated with extreme rapidity, producing an explosive prrt (Fig. 1, A) and the bird jumps forward about 15 cm as
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