On the behavioural ecology and vocal communication of the brown-headed parrot (Poicephalus cryptoxanthus)

Abstract

The Brown-headed Parrot (Poicephalus cryptoxanthus) is a poorly known species inhabiting open woodland in south-eastern Africa. This study elucidates critical aspects of the species ecology and although each of these categories impinge on one another, it concentrates on two broad biological aspects, diet and breeding biology, and vocalizations. The species has a generalist diet, switching from one suite of food species to another as and when those species become available, with no species critical for its survival. Analysis of dietary items throughout the year and comparison with handling times and availability reveals that at no time is the species under dietary constraint. Evidence from association indices and behavioural observation shows that the popular view that the Brown-headed Parrot forms pairs just before breeding is erroneous. Birds retain pair bonds and the bond is long-term, lasting at least throughout the year. Congregations are therefore of a classical fission/fusion type with the sub-units being the paired males and females. A mathematical model of the growth of captive chicks is presented, as a guideline to alert potential breeders of Brown-headed Parrots of malnutrition or disease. The species is a secondary cavity hole nester and whilst, the breeding biology of the species is summarised, the importance of large and old trees for breeding opportunities of the species is emphasised. This theme is continued by testing various adaptive hatching hypotheses as possible explanations of asynchronous hatching in the species. It is suggested that asynchronous hatching may be an adaptive strategy moderating against the number of suitable nesting cavities. The vocalization repertoire of the Brown-headed Parrot is described and seven separate vocalizations are recognized. None of these are associated with sexual situations, offering further evidence of a long-term pair bond. Evidence is offered that Brown-headed Parrot chicks can recognise their parents from individual vocal signatures supporting previous evidence from a number of species where chicks may mingle with unrelated chicks. Conversely, parents seem to be unable to recognise their chicks in the same way. It is concluded that this inability may be a result of strong one-way selection pressure, where the costs outweigh the benefits for parents with more than one chick or may be related to the experimental design. Individual recognition by voice implies individual voice differences and the adult double chip contact call is analysed using multivariate statistical techniques. The analysis separates individuals on the basis of frequency and temporal patterns and it is concluded that these parameters may allow individual voice differentiation. Finally, high frequency aspects of the double chip contact call are examined. These frequencies lie above the normally accepted upper threshold of avian hearing. From laboratory and field experiments, behavioural evidence is presented suggesting that the Brown-headed Parrot reacts to these frequencies and may use their degradation as a means of ranging distances to conspecifics.