|dc.description.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