Breeding Season Diets of Egrets in Southeast Australia: Implications for Future Population Viability

Abstract

Abstract Populations of egrets and other waterbirds in the Murray-Darling Basin of eastern Australia are declining. River regulation and increasing frequency of droughts are considered to be mainly responsible by reducing the frequency and extent of flooding to temporary wetlands. However, other changes have occurred to wetlands, such as the introduction of non-native fish, widespread severe declines in the abundance of native fish, increased salinity, sediment and nutrient concentrations, and removal of aquatic vegetation by livestock grazing. Current knowledge of the diets of egrets is inadequate for an assessment of any ecological implications arising from these changes. In this study the breeding season diets of Eastern Great Egret Ardea modesta and Intermediate Egret A. intermedia were quantified at a colony in the Murray Basin. Eastern Great Egrets depended mainly on introduced Common Carp Cyprinus carpio (94% of diet biomass), a species regarded as a severe pest of river systems and wetlands within...