EMU Vol. 100, 161-168, 2000 © Royal Australasian Ornithologists Union 2000 0158-4197/00/03161 + 7 10.1071/MU9902 Received 16-1-1999, accepted 30-4-1999 Social Mating System and Sexual Behaviour in Captive Emus Dromaius novaehollandiae Dominique Blache, 1 Carl D. Barrett and Graeme B. Martin Faculty of Agriculture (Animal Science), The University of Western Australia, Nedlands, WA 6907 1 Corresponding author Summary: 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 tech- niques that permit determination of chick parentage. The Emu Dromaius novaehollandiae, a flightless ratite that is endemic to Australia, is a prolific breeder with an annual reproductive cycle in which egg-laying and sperm production start around autumn and last until late winter (North 1889; Serventy & Whittell 1962; Malecki et al. 1998). The mating relations and sexual behaviour of the species have been described in earlier studies. Male and female Emus display courtship conspicuous- ly, as is typical of ratites (Handford & Mares 1985). Both sexes vocalise strongly, with the females produc- ing a high intensity resonant boom (‘drumming’) while the males produce a shorter, coarser ‘grunting’ sound (Fleay 1936; Curry 1979; Davies 1966 cited in O’Brien 1990). Both sexes fluff out the feathers on the front of the neck in communicative postures (Fleay 1936; Curry 1979; Coddington & Cockburn 1995), and they both will often curve their necks into a slight ‘S-shape’ and, when they identify with each other, will raise their heads (Malecki 1993). Males may then attempt to fol- low the female and place their heads over the female’s back or nape. Females show their interest by gradually lowering their heads, raising their tails and crouching into the mating position (Malecki 1993). Generally, Emus are quite docile but, during the breeding season, they become much more aggressive (Long 1959; Lack 1968; Davies 1976a). Coddington & Cockburn (1995) noted that females are the more aggressive sex at this time, mostly towards females attempting to court their partner. The earliest documentation of mating relations in Emus stems back to Gaukrodger (1925) who noted that paired birds commonly occupied nesting sites, although in one out of an unknown number of observations, three birds were around the same nest. Other studies, based on observations of wild birds, classified the species as monogamous (Davies 1972; Davies 1976a; Handford & Mares 1985), although deviations towards polygamous relations were contrived with females in captivity (Fleay 1936; Kendeigh 1952). Long (1959) also reported small groups of two and three during the breeding sea- son and made specific reference to two males courting the same female for a long period of time. A recent and more detailed field study by Coddington & Cockburn (1995) clarified the situation by showing that the male can be both monogamous and polygamous and that the female mating pattern involves a combination of monogamy, polygamy and promiscuity. The detailed descriptions of courtship behaviour of Emus have not been supported by quantitative studies of the social mating system of the species, a necessity if 161