Social mating system and sexual behaviour in captive emus Dromaius novaehollandiae

Previous studies based on field observations have described the sexual beha viour of emus, but the social mating system of the species remains uncertai n because of the lack of quantitative and detailed data. We therefore place d individually identified birds, 33 females and 27 males, in a large ge fre e-range pen (2.5 km(2)) and recorded their behaviour twice weekly for 11 we eks, from the beginning of the laying period until all the males had begun incubating. The behaviour of both birds involved in a stable pair relations hip was recorded in detail during 16 sets of one-hour observations. Over 70 % of males and females were classified as;socially monogamous', but 7% of m ales and 3% of females were classified as 'socially polygamous'. Also, 15% of the females were engaged in sequential polyandry. Within the pair, the f emales were the most active in pair formation and maintenance, directed the ir behaviour primarily towards their mate, and also protected access to the ir mate. Conversely, before they began incubating, the males were prompt to court females other than their mates and often walked away from their mate s. Factor analysis reinforced these observations showing that female behavi our is mainly directed towards the mate whereas male behaviour has a major promiscuous component. We concluded that the social mating system of the em u is of a monogamous type but a few individuals are promiscuous - the males before they start incubating, and the females after their mate has started incubating, in addition, there are significant numbers of extra-pair copul ations. The potential contribution of this relatively small proportion of p romiscuous behaviours to the reproductive success of individuals cannot be assessed from behavioural studies and remains to be established by techniqu es that permit determination of chick parentage.