Beschreibung:
<jats:sec><jats:title>Abstract</jats:title><jats:p>In a flock of tame, free-flying bar-headed geese (Anser indicus) the structure, stability and causes of the dominance hierarchy among different types of social units were studied. 1. In accordance with field results of other authors, families proved dominant over pairs, pairs over unpaired birds, and single males dominated single females. Single females with young ranked between families and pairs in this study, and lone breeding males whose females were incubating ranked between pairs and unpaired individuals. Contrary to some field studies, no rank differences were found between different-sized families. 2. The dominance value of pairs in winter correlated with subsequent fledging success, and there was some casual evidence that high-ranking males are more likely to obtain a mate. This would result in relating high rank to families, medium rank to pairs and low rank to unpaired birds. Yet as temporarily leaving the mate was promptly followed by a drop in rank and successful breeding by a rise in rank, the social context seems a major cause, and only to a minor extent a consequence of dominance rank. 3. Age correlated more strongly with a pair's rank in winter than weight, tarsus length and upper beak length. Rank in summer correlated highly with rank in the following winter. A positive feedback system age - dominance - fledging success-higher dominance-fledging success' is suggested which could account for the 'delayed breeding' common in geese and swans. 4. In pairs or families male age correlated more strongly than female age with winter dominance. Most opponents were displayed by the male alone, and only the male of a pair got involved in highest intensity aggression (wing-beat fighting). The widowed female of one high-ranking pair was low-ranking in subsequent years when paired with a young low-ranking male. The evidence suggests that the gander alone determines a family's or pair's rank. 5. There was no indication of a positive co-operative effect achieved by joint aggression. Comparison of frequencies of aggressive acts and postures between birds in different social contexts suggested that the presence of the mate and/or offspring increases fighting motivation, thus explaining the dependence of rank on the social context. 6. The stability of dyadic dominance relationships between social units was greater between than within social classes. The hierarchy of social classes can be explained by geese signalling their degree of fighting motivation to each other. Individual recognition of members of other social units seems of minor importance for the hierarchy even in this stable flock.</jats:p>
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