The Foraging Ecology of Egrets in Rice Fields in Southern New South Wales, Australia

Abstract

-Numbers of wading birds are declining throughout the Murray-Darling Basin in Australia, and the loss of wetland habitats to agriculture is the most likely cause. This study describes the foraging of egrets in irrigated rice fields that occur extensively in areas of former wetlands. Tadpoles were the main prey of Great and Intermediate Egrets (Ardea alba and A. intermedia), with insects important secondary prey. Insects were the main prey of Cattle Egrets (A. ibis). Prey capture rates for Great and Intermediate Egrets declined by around 40% between November and January as the rice plants grew from seedling to mature stages. Cattle Egret prey capture rates did not decline. The abundance of tadpoles and most aquatic insects in the rice fields declined significantly between November and February. All three egret species laid eggs mainly during December and had young in the nest duringJanuary and February. Thus the declining profitability of rice fields as foraging sites coincided with the maximum demand for food by the birds to rear their young. Rice fields may not be an adequate substitute for natural wetlands for Great and Intermediate Egrets. Received 14 February 2001, accepted 20 March 2001.