Abstract

Previous studies based on field observations have described the sexual behaviour of emus, but the social mating system of the species remains uncertain because of the lack of quantitative and detailed data. We therefore placed individually identified birds, 33 females and 27 males, in a large free-range pen (2.5 km 2 ) and recorded their behaviour twice weekly for 11 weeks, from the beginning of the laying period until all the males had begun incubating. The behaviour of both birds involved in a stable pair relationship 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 males and 3% of females were classified as ‘socially polygamous’. Also, 15% of the females were engaged in sequential polyandry. Within the pair, the females were the most active in pair formation and maintenance, directed their behaviour primarily towards their mate, and also protected access to their mate. Conversely, before they began incubating, the males were prompt to court females other than their mates and often walked away from their mates. Factor analysis reinforced these observations showing that female behaviour is mainly directed towards the mate whereas male behaviour has a major promiscuous component. We concluded that the social mating system of the emu 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 copulations. The potential contribution of this relatively small proportion of promiscuous behaviours to the reproductive success of individuals cannot be assessed from behavioural studies and remains to be established by techniques that permit determination of chick parentage.