The Mating System of Free-Living Emus

Abstract

Despite their pivotal role in interpretation of the complex mating systems of the ratites, the mating system of free-living emus (Dromaius novaehollandiae) has not been characterised. Here we report observations on an introduced but free-ranging population of emus at Tidbinbilla Nature Reserve in the Australian Capital Territory. Emus combined monogamy, polyandry and promiscuity. All initially unpaired males paired with and incubated a clutch for females whose primary mates were preoccupied with incubation. However, females were also promiscuous, and most copulations we observed were extra-pair. Females fight vigorously among themselves for access to unpaired males. Coupled with observations on cassowaries, these data suggest that there is no simple correlation between habitat (grassland/forest) and the mating system in ratites. Instead, the resolution of the complex conflicts of interest between the sexes appears to determine the predominant mating systems exhibited by a species.