Waterbird Use of Rice Fields in Australia

Rice (Oryza saliva) growing in Australia occurs almost exclusively in the south-east, in the Riverine Plains of the Murray-Darling Basin, with an annual average of 110,000 ha. All crops are grown under irrigation using water abstracted from rivers. Rice fields are flooded between October and March and are dry otherwise. A large decrease in natural wetland extent and declines in most waterbird populations have been associated with the increase in irrigated agriculture since the 1960s. The ecology of waterbirds in rice fields has been studied in only one area, around Fivebough Swamp in southern New South Wales. Thirty-seven waterbird species were recorded in rice fields compared with 70 species on an adjacent natural wetland. Species diversity and the abundance of individual species declined as the rice crops developed so that most species used rice fields for only one to two months after flooding. An increase in water depths associated with the timing of panicle initiation of the rice plants was probably the main cause, but declines in most waterbird prey species also occurred as the crops developed. Rice crops were particularly important feeding areas for Glossy Ibis (Plegadis falcinellus) during November and December. Small numbers of the threatened Australasian Bittern (Botaurus poiciloptilus) were also recorded. Received 23 October 2007, accepted 23 January 2009.