Brown-headed parrots Poicephalus cryptoxanthus inhabit open woodland in eastern Southern Africa. During long-term studies of this species we independently recorded calls from this species which range above 10 kHz. This frequency is generally believed to be the upper limit of avian vocalisation frequencies. To test whether these frequencies are perceived by the birds or are functionless artefact of the sound producing mechanism, we conducted a series of playback experiments on both captive and wild individuals. Twelve contact calls, of which four were complete, four had all elements above 10 kHz filtered out and four had all elements below 10 kHz removed, were used. The call sequence was randomised through a total time of 40 minutes per session. A gradient of reactions was recorded with the strongest being in response to the unfiltered call. We suggest that this gradation of reactions shows that Brown-headed parrot are capable of perceiving high frequency elements although the manner of production and receiving is unknown. We propose that this species uses high frequency elements in their calls to judge the distances between conspecific calls. We further provide evidence that the ability to emit calls in this high frequency range is not limited to Brown- headed parrots and offer sonograms of other parrot species which also demonstrate this capability.
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