Agnostic behaviour and mate selection in the mallard (Anas platyrhynchos).

The social behaviour of mallards was studied in groups of captive, individually marked birds. In Autumn the mallards rapidly formed stable, near-linear, agonistic dominance hierarchies in groups of initially unfamiliar birds. Fights and overt aggressive behaviour were initially quite common but rapidly declined. The mallards rapidly learnt about the outcomes of agonistic encounters. Rank was inversely correlated with the number of, avoids performed but was not correlated with aggressive behaviours, age, weight or sex. In Spring fights between males became common and the agonistic dominance hierarchy was unstable. Females performed much less agonistic behaviour. One group was observed at intervals over four years. Most birds remained with the same mate. The males tended to retain roughly the same rank in the hierarchy. The changes in the pattern of agonistic behaviour were discussed in relation to the changing costs and benefits of the behaviour over the year. The failure of game theory models to predict the agonistic behaviour exhibited in a group of birds was discussed. Agonistic behaviour was also important in mate selection. When single females were introduced to a group of males the top ranking male sometimes monopolised the female and usually paired with her. When several females were introduced to a group of males male rank was the most important cue determining female preference; the degree of damage to the plumage was also used as a cue by females. Males whose plumage had been damaged artificially were not chosen by females. The cues which were used by the females indicated male phenotype quality. In a monogamous mating system the eventual mate may not have been the most preferred mate. The discussion extended to a consideration of the constraints imposing monogamy on mallards and the nature of the species identifying mechanism.