The inter-animal control of space is here illustrated by comparative studies. Related species of parrots which are found from wet to semi-arid and arid habitats are investigated. As the habitat becomes more arid the species become more gregarious. Social complexity however follows a quite different course. It is Zow in the wet habitats but rises rapidly to a maximum in the semi-arid habitats, and from there falls gradually as aridity and gregariousness increase.
Gregariousness is measured by flock size and social index. Data for flock size comes from the number seen flying together and feeding together. Social index is the subjective assessment of morphological and behavioural characteristics. The more similar the sex and age groups are, the higher is the index.
Complexity of the social system is assessed by studying the communication system, and the role of definable individuals and groups in the system. For example, the semi-arid adapted species (plat-ycercus eximius) has at least 27 distinct auditory signals, while the arid adapted species (Barnardius barnardi), has l6 and the wet adapted species (P. elegans) has 20. The semi-arid adapted species is composed of a core population of dominant pairs and a secondary population which forms groups within a flock. The groups are arranged in a hierarchy, and the individuals within a group are also arranged in a hierarchy. Species of the wet forests and the arid areas have fewer recognisable social entities.
KeywordsCore Population Auditory Signal Social Complexity Flock Size Population System
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